VB.Net Tutorial/GUI/TextBox

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Change TextBox font by RadioButton and CheckBox

Imports System.Windows.Forms
public class RadioButtonControlFont
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class

Public Class Form1
    Public mysize As Integer
    Public mybold As Boolean
    Public myItalic As Boolean
    Private Sub RadioButton1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
        CheckBox1.Checked = 1
    End Sub
    Private Sub CheckBox1_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox1.CheckedChanged
        myItalic = Not myItalic
        TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Regular)
        If myItalic And mybold Then
            TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Italic)
        ElseIf myItalic Then
            TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Italic)
        ElseIf mybold Then
            TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Bold)
        End If
    End Sub
    Private Sub GroupBox1_Enter(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles GroupBox1.Enter
    End Sub
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        mybold = False
        myItalic = False
        mysize = 25
    End Sub
    Private Sub RadioButton1_CheckedChanged_1(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButton1.CheckedChanged
        mysize = 36
        TextBox1.Font = New System.Drawing.Font("", mysize)
    End Sub
    Private Sub RadioButton2_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles RadioButton2.CheckedChanged
        mysize = 25
        TextBox1.Font = New System.Drawing.Font("", mysize)
    End Sub
    Private Sub CheckBox2_CheckedChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles CheckBox2.CheckedChanged
        mybold = Not mybold
        TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Regular)
        If myItalic And mybold Then
            TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Bold)
        ElseIf myItalic Then
            TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Italic)
        ElseIf mybold Then
            TextBox1.Font = New System.Drawing.Font("", mysize, Drawing.FontStyle.Bold)
        End If
    End Sub
End Class
<Global.Microsoft.VisualBasic.rupilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form
    "Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.CheckBox1 = New System.Windows.Forms.CheckBox
        Me.CheckBox2 = New System.Windows.Forms.CheckBox
        Me.GroupBox1 = New System.Windows.Forms.GroupBox
        Me.RadioButton1 = New System.Windows.Forms.RadioButton
        Me.RadioButton2 = New System.Windows.Forms.RadioButton
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.GroupBox1.SuspendLayout()
        Me.SuspendLayout()
        "
        "CheckBox1
        "
        Me.CheckBox1.AutoSize = True
        Me.CheckBox1.Location = New System.Drawing.Point(230, 34)
        Me.CheckBox1.Name = "CheckBox1"
        Me.CheckBox1.Size = New System.Drawing.Size(48, 16)
        Me.CheckBox1.TabIndex = 1
        Me.CheckBox1.Text = "Italic"
        Me.CheckBox1.UseVisualStyleBackColor = True
        "
        "CheckBox2
        "
        Me.CheckBox2.AutoSize = True
        Me.CheckBox2.Location = New System.Drawing.Point(230, 56)
        Me.CheckBox2.Name = "CheckBox2"
        Me.CheckBox2.Size = New System.Drawing.Size(48, 16)
        Me.CheckBox2.TabIndex = 2
        Me.CheckBox2.Text = "Bold"
        Me.CheckBox2.UseVisualStyleBackColor = True
        "
        "GroupBox1
        "
        Me.GroupBox1.Controls.Add(Me.RadioButton2)
        Me.GroupBox1.Controls.Add(Me.RadioButton1)
        Me.GroupBox1.Location = New System.Drawing.Point(224, 85)
        Me.GroupBox1.Name = "GroupBox1"
        Me.GroupBox1.Size = New System.Drawing.Size(132, 77)
        Me.GroupBox1.TabIndex = 3
        Me.GroupBox1.TabStop = False
        Me.GroupBox1.Text = "Font size"
        "
        "RadioButton1
        "
        Me.RadioButton1.AutoSize = True
        Me.RadioButton1.Location = New System.Drawing.Point(6, 20)
        Me.RadioButton1.Name = "RadioButton1"
        Me.RadioButton1.Size = New System.Drawing.Size(59, 16)
        Me.RadioButton1.TabIndex = 1
        Me.RadioButton1.TabStop = True
        Me.RadioButton1.Text = "Larger font"
        Me.RadioButton1.UseVisualStyleBackColor = True
        "
        "RadioButton2
        "
        Me.RadioButton2.AutoSize = True
        Me.RadioButton2.Location = New System.Drawing.Point(6, 42)
        Me.RadioButton2.Name = "RadioButton2"
        Me.RadioButton2.Size = New System.Drawing.Size(59, 16)
        Me.RadioButton2.TabIndex = 2
        Me.RadioButton2.TabStop = True
        Me.RadioButton2.Text = "Smaller font"
        Me.RadioButton2.UseVisualStyleBackColor = True
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(12, 12)
        Me.TextBox1.Multiline = True
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(195, 150)
        Me.TextBox1.TabIndex = 4
        Me.TextBox1.Text = "www.vbex.ru"
        "
        "Form1
        "
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 12.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(368, 174)
        Me.Controls.Add(Me.TextBox1)
        Me.Controls.Add(Me.GroupBox1)
        Me.Controls.Add(Me.CheckBox2)
        Me.Controls.Add(Me.CheckBox1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.GroupBox1.ResumeLayout(False)
        Me.GroupBox1.PerformLayout()
        Me.ResumeLayout(False)
        Me.PerformLayout()
    End Sub
    Friend WithEvents CheckBox1 As System.Windows.Forms.CheckBox
    Friend WithEvents CheckBox2 As System.Windows.Forms.CheckBox
    Friend WithEvents GroupBox1 As System.Windows.Forms.GroupBox
    Friend WithEvents RadioButton2 As System.Windows.Forms.RadioButton
    Friend WithEvents RadioButton1 As System.Windows.Forms.RadioButton
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
End Class

Comprehensive Demo for TextBox

"Programming .Net Windows Applications [ILLUSTRATED] (Paperback)
"by Jesse Liberty (Author), Dan Hurwitz (Author)
"# Publisher: O"Reilly Media, Inc.; 1 edition (October 28, 2003)
"# Language: English
"# ISBN-10: 0596003218
"# ISBN-13: 978-0596003210
imports System
imports System.Drawing
imports System.Windows.Forms
imports System.Text
namespace ProgrammingWinApps
  public class TextBoxes : inherits Form
    dim yDelta as integer
    dim yPos as integer = 20
    dim txtSingle as TextBox
    dim txtMulti as TextBox
    dim txtDisplay as TextBox
    dim btn as Button
    dim txtBoxes(1) as TextBox
    public sub New()
            Text = "TextBoxes"
      Size = new Size(450,375)
      dim lblSingle as new Label()
      lblSingle.Parent = me
      lblSingle.Text = "Single Line TextBox:"
      lblSingle.Location = new Point(10,yPos)
      lblSingle.Size = new Size(150,20)
      lblSingle.TextAlign = ContentAlignment.MiddleRight
      yDelta = lblSingle.Height + 10
      txtSingle = new TextBox()
      txtSingle.Parent = me
      txtSingle.Text = "Single Line"
      txtSingle.Size = new Size(200, txtSingle.PreferredHeight)
      txtSingle.Location = new Point(lblSingle.Left + _
                      lblSingle.Size.Width, yPos)
      txtSingle.Multiline = false
      txtSingle.BorderStyle = BorderStyle.Fixed3D
      dim lblMulti as new Label()
      lblMulti.Parent = me
      lblMulti.Text = "Multi Line TextBox:"
      lblMulti.Location = new Point(10, yPos + yDelta)
      lblMulti.Size = new Size(150,20)
      lblMulti.TextAlign = ContentAlignment.MiddleRight
      txtMulti = new TextBox()
      txtMulti.Parent = me
      txtMulti.Text = "Multi Line"
      txtMulti.Size = new Size(200,100)
      txtMulti.Location = new Point(lblMulti.Left + _
                  lblMulti.Size.Width, yPos + yDelta)
      txtMulti.AcceptsTab = true
      txtMulti.Multiline = true
      txtMulti.BorderStyle = BorderStyle.Fixed3D
      txtMulti.ScrollBars = ScrollBars.Vertical
      btn = new Button()
      btn.Parent = me
      btn.Text = "Show MultiLines"
      btn.Location = new Point(lblMulti.Left + _
              lblMulti.Size.Width, yPos + (5 * yDelta))
      AddHandler btn.Click, AddressOf btn_Click
      dim xSize as integer = CType((Font.Height * .75) * _
              btn.Text.Length, integer)
      dim ySize as integer = Font.Height + 10
      btn.Size = new Size(xSize, ySize)
      txtDisplay = new TextBox()
      txtDisplay.Parent = me
      txtDisplay.Text = ""
      txtDisplay.Size = new Size(200,100)
      txtDisplay.Location = new Point(lblMulti.Left + _
                lblMulti.Size.Width, yPos + (6 * yDelta))
      txtDisplay.Multiline = true
      txtDisplay.BorderStyle = BorderStyle.FixedSingle
      txtDisplay.BackColor = Color.LightGray
      txtDisplay.ScrollBars = ScrollBars.Vertical
      txtDisplay.ReadOnly = true
      "  Fill the array of TextBoxes
      txtBoxes(0) = txtSingle
      txtBoxes(1) = txtMulti
      "  Menus
      "  Edit menu items
      dim mnuDash1 as new MenuItem("-")
      dim mnuDash2 as new MenuItem("-")
      dim mnuUndo as new MenuItem("&Undo", _
                 new EventHandler(AddressOf mnuUndo_Click), _
                 Shortcut.CtrlZ)
      dim mnuCut as new MenuItem("Cu&t", _
              new EventHandler(AddressOf mnuCut_Click), _
              Shortcut.CtrlX)
      dim mnuCopy as new MenuItem("&Copy", _
              new EventHandler(AddressOf mnuCopy_Click), _
              Shortcut.CtrlC)
      dim mnuPaste as new MenuItem("&Paste", _
              new EventHandler(AddressOf mnuPaste_Click), _
              Shortcut.CtrlV)
      dim mnuDelete as new MenuItem("&Delete", _
              new EventHandler(AddressOf mnuDelete_Click))
      dim mnuSelectAll as new MenuItem("Select &All", _
              new EventHandler(AddressOf mnuSelectAll_Click), _
              Shortcut.CtrlA)
      dim mnuSelect5 as new MenuItem("Select First &5", _
              new EventHandler(AddressOf mnuSelect5_Click), _
              Shortcut.Ctrl5)
      dim mnuClear as new MenuItem("Clea&r", _
              new EventHandler(AddressOf mnuClear_Click))
      dim mnuEdit as new MenuItem("&Edit", _
              new MenuItem() {mnuUndo, mnuDash1, _
              mnuCut, mnuCopy, mnuPaste, mnuDelete, mnuDash2, _
              mnuSelectAll, mnuSelect5, mnuClear})
      "  View Menu items
      dim mnuScrollToCaret as new MenuItem("&Scroll to Caret", _
              new EventHandler(AddressOf mnuScrollToCaret_Click))
      dim mnuView as new MenuItem("&View", _
              new MenuItem() {mnuScrollToCaret})
      
      "  Main menu
      Menu = new MainMenu(new MenuItem() {mnuEdit, mnuView})

    end sub  "  close for constructor
    public shared sub Main() 
      Application.Run(new TextBoxes())
    end sub
    private sub mnuUndo_Click(ByVal sender As Object, _
                ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          if txt.CanUndo = true then
            txt.Undo()
            txt.ClearUndo()
          end if
        end if
      next
    end sub
    private sub mnuCut_Click(ByVal sender As Object, _
                  ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          if txt.SelectedText <> "" then
            txt.Cut()
          end if
        end if
      next
    end sub
    private sub mnuCopy_Click(ByVal sender As Object, _
                  ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          if txt.SelectionLength > 0 then
            txt.Copy()
          end if
        end if
      next
    end sub
    private sub mnuPaste_Click(ByVal sender As Object, _
                  ByVal e As EventArgs)
      if Clipboard.GetDataObject().GetDataPresent(DataFormats.Text) = true then
        dim i as integer
        for i = 0 to txtBoxes.Length - 1
          if txtBoxes(i).Focused then
            dim txt as TextBox = CType(txtBoxes(i), TextBox)
            if txt.SelectionLength > 0 then
              if MessageBox.Show( _
              "Do you want to overwrite the currently selected text?", _
              "Cut & Paste", MessageBoxButtons.YesNo) = _
                    DialogResult.No then
                txt.SelectionStart = txt.SelectionStart + _
                          txt.SelectionLength
              end if
            end if
            txt.Paste()
          end if
        next
      end if
    end sub
    private sub mnuDelete_Click(ByVal sender As Object, _
                  ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          if txt.SelectionLength > 0 then
            txt.SelectedText = ""
          end if
        end if
      next
    end sub
    private sub mnuClear_Click(ByVal sender As Object, _
                  ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          txt.Clear()
        end if
      next
    end sub
    private sub mnuSelect5_Click(ByVal sender As Object, _
                    ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          if txt.Text.Length >= 5 then
            txt.Select(0,5)
          else
            txt.Select(0,txt.Text.Length)
          end if
        end if
      next
    end sub
    private sub mnuSelectAll_Click(ByVal sender As Object, _
                    ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          txt.SelectAll()
        end if
      next
    end sub
    private sub mnuScrollToCaret_Click(ByVal sender As Object, _
                      ByVal e As EventArgs)
      dim i as integer
      for i = 0 to txtBoxes.Length - 1
        if txtBoxes(i).Focused then
          dim txt as TextBox = CType(txtBoxes(i), TextBox)
          txt.ScrollToCaret()
        end if
      next
    end sub
    private sub btn_Click(ByVal sender as object, _
                ByVal e as EventArgs)
      " Create a string array to hold the Lines property.
      dim arLines(txtMulti.Lines.Length - 1) as string
      arLines = txtMulti.Lines
      "  Use stringBuilder for efficiency.
      dim str as string = "Line" + vbTab + "String" + vbCrLf
      dim sb as new StringBuilder()
      sb.Append(str)
      " Iterate through the array & display each line.
      dim i as integer
      for i = 0 to arLines.Length - 1
        str = i.ToString() + "." + vbTab + arLines(i) + vbCrLf
        sb.Append(str)
      next
      txtDisplay.Text = sb.ToString()
    end sub
  end class
end namespace

Convert input value in a TextField

Imports System.Windows.Forms
<Global.Microsoft.VisualBasic.rupilerServices.DesignerGenerated()> _
Partial Class ConvertForm
    Inherits System.Windows.Forms.Form
    "Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.SourceFahrenheit = New System.Windows.Forms.RadioButton
        Me.SourceCelsius = New System.Windows.Forms.RadioButton
        Me.SourceKelvin = New System.Windows.Forms.RadioButton
        Me.ValueFahrenheit = New System.Windows.Forms.TextBox
        Me.ValueCelsius = New System.Windows.Forms.TextBox
        Me.ValueKelvin = New System.Windows.Forms.TextBox
        Me.ConvertTemperature = New System.Windows.Forms.Button
        Me.SuspendLayout()
        "
        "SourceFahrenheit
        "
        Me.SourceFahrenheit.AutoSize = True
        Me.SourceFahrenheit.Checked = True
        Me.SourceFahrenheit.Location = New System.Drawing.Point(16, 24)
        Me.SourceFahrenheit.Name = "SourceFahrenheit"
        Me.SourceFahrenheit.Size = New System.Drawing.Size(75, 17)
        Me.SourceFahrenheit.TabIndex = 0
        Me.SourceFahrenheit.TabStop = True
        Me.SourceFahrenheit.Text = "&Fahrenheit"
        Me.SourceFahrenheit.UseVisualStyleBackColor = True
        "
        "SourceCelsius
        "
        Me.SourceCelsius.AutoSize = True
        Me.SourceCelsius.Location = New System.Drawing.Point(16, 56)
        Me.SourceCelsius.Name = "SourceCelsius"
        Me.SourceCelsius.Size = New System.Drawing.Size(58, 17)
        Me.SourceCelsius.TabIndex = 2
        Me.SourceCelsius.Text = "&Celsius"
        Me.SourceCelsius.UseVisualStyleBackColor = True
        "
        "SourceKelvin
        "
        Me.SourceKelvin.AutoSize = True
        Me.SourceKelvin.Location = New System.Drawing.Point(16, 88)
        Me.SourceKelvin.Name = "SourceKelvin"
        Me.SourceKelvin.Size = New System.Drawing.Size(53, 17)
        Me.SourceKelvin.TabIndex = 4
        Me.SourceKelvin.Text = "&kelvin"
        Me.SourceKelvin.UseVisualStyleBackColor = True
        "
        "ValueFahrenheit
        "
        Me.ValueFahrenheit.Location = New System.Drawing.Point(120, 24)
        Me.ValueFahrenheit.Name = "ValueFahrenheit"
        Me.ValueFahrenheit.Size = New System.Drawing.Size(100, 20)
        Me.ValueFahrenheit.TabIndex = 1
        "
        "ValueCelsius
        "
        Me.ValueCelsius.Location = New System.Drawing.Point(120, 56)
        Me.ValueCelsius.Name = "ValueCelsius"
        Me.ValueCelsius.Size = New System.Drawing.Size(100, 20)
        Me.ValueCelsius.TabIndex = 3
        "
        "ValueKelvin
        "
        Me.ValueKelvin.Location = New System.Drawing.Point(120, 88)
        Me.ValueKelvin.Name = "ValueKelvin"
        Me.ValueKelvin.Size = New System.Drawing.Size(100, 20)
        Me.ValueKelvin.TabIndex = 5
        "
        "ConvertTemperature
        "
        Me.ConvertTemperature.Location = New System.Drawing.Point(144, 128)
        Me.ConvertTemperature.Name = "ConvertTemperature"
        Me.ConvertTemperature.Size = New System.Drawing.Size(75, 23)
        Me.ConvertTemperature.TabIndex = 6
        Me.ConvertTemperature.Text = "Convert"
        Me.ConvertTemperature.UseVisualStyleBackColor = True
        "
        "ConvertForm
        "
        Me.AcceptButton = Me.ConvertTemperature
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(245, 169)
        Me.Controls.Add(Me.ConvertTemperature)
        Me.Controls.Add(Me.ValueKelvin)
        Me.Controls.Add(Me.ValueCelsius)
        Me.Controls.Add(Me.ValueFahrenheit)
        Me.Controls.Add(Me.SourceKelvin)
        Me.Controls.Add(Me.SourceCelsius)
        Me.Controls.Add(Me.SourceFahrenheit)
        Me.FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedSingle
        Me.MaximizeBox = False
        Me.MinimizeBox = False
        Me.Name = "ConvertForm"
        Me.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen
        Me.Text = "Convert Temperatures"
        Me.ResumeLayout(False)
        Me.PerformLayout()
    End Sub
    Friend WithEvents SourceFahrenheit As System.Windows.Forms.RadioButton
    Friend WithEvents SourceCelsius As System.Windows.Forms.RadioButton
    Friend WithEvents SourceKelvin As System.Windows.Forms.RadioButton
    Friend WithEvents ValueFahrenheit As System.Windows.Forms.TextBox
    Friend WithEvents ValueCelsius As System.Windows.Forms.TextBox
    Friend WithEvents ValueKelvin As System.Windows.Forms.TextBox
    Friend WithEvents ConvertTemperature As System.Windows.Forms.Button
End Class
Public Class ConvertForm
    Private Sub ConvertTemperature_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ConvertTemperature.Click
        On Error Resume Next
        If (SourceFahrenheit.Checked = True) Then
            If (IsNumeric(ValueFahrenheit.Text) = True) Then
                ValueCelsius.Text = _
                   (Val(ValueFahrenheit.Text) - 32) / 1.8
                ValueKelvin.Text = _
                   ((Val(ValueFahrenheit.Text) - 32) / 1.8) + 273.15
            Else
                ValueCelsius.Text = "Error"
                ValueKelvin.Text = "Error"
            End If
        ElseIf (SourceCelsius.Checked = True) Then
            If (IsNumeric(ValueCelsius.Text) = True) Then
                ValueFahrenheit.Text = _
                   (Val(ValueCelsius.Text) * 1.8) + 32
                ValueKelvin.Text = Val(ValueCelsius.Text) + 273.15
            Else
                ValueFahrenheit.Text = "Error"
                ValueKelvin.Text = "Error"
            End If
        Else
            If (IsNumeric(ValueKelvin.Text) = True) Then
                ValueFahrenheit.Text = _
                   ((Val(ValueKelvin.Text) - 273.15) * 1.8) + 32
                ValueCelsius.Text = Val(ValueKelvin.Text) - 273.15
            Else
                ValueFahrenheit.Text = "Error"
                ValueCelsius.Text = "Error"
            End If
        End If
    End Sub
End Class

public class FahrenheitCelsiusConverter
    Public Shared Sub Main()
        Application.Run(New ConvertForm)
    End Sub
End Class

Copy selection text from a TextBox and paste to another

Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Windows.Forms
public class TextBoxCopyPaste
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class
Public Class Form1
    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
    Public Sub New()
        MyBase.New()
        "This call is required by the Windows Form Designer.
        InitializeComponent()
        "Add any initialization after the InitializeComponent() call
    End Sub
    "Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents TextBox2 As System.Windows.Forms.TextBox
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.Button1 = New System.Windows.Forms.Button
        Me.Label1 = New System.Windows.Forms.Label
        Me.TextBox2 = New System.Windows.Forms.TextBox
        Me.SuspendLayout()
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(128, 72)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(112, 20)
        Me.TextBox1.TabIndex = 0
        Me.TextBox1.Text = ""
        "
        "Button1
        "
        Me.Button1.Location = New System.Drawing.Point(128, 120)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(112, 23)
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "Copy Selected Text"
        "
        "Label1
        "
        Me.Label1.Font = New System.Drawing.Font("Microsoft Sans Serif", 24.0!, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
        Me.Label1.Location = New System.Drawing.Point(0, 0)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(344, 48)
        Me.Label1.TabIndex = 2
        Me.Label1.Text = "Copying Selected Text"
        "
        "TextBox2
        "
        Me.TextBox2.Location = New System.Drawing.Point(128, 168)
        Me.TextBox2.Name = "TextBox2"
        Me.TextBox2.Size = New System.Drawing.Size(112, 20)
        Me.TextBox2.TabIndex = 3
        Me.TextBox2.Text = ""
        "
        "Form1
        "
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(360, 253)
        Me.Controls.Add(Me.TextBox2)
        Me.Controls.Add(Me.Label1)
        Me.Controls.Add(Me.Button1)
        Me.Controls.Add(Me.TextBox1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
    End Sub
#End Region
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox1.Copy()
        TextBox2.Paste()
    End Sub
End Class

Create PasswordField by setting the TextBox.PasswordChar

Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Windows.Forms
public class PasswordFieldByTextBox
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class
Public Class Form1
    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
    Public Sub New()
        MyBase.New()
        "This call is required by the Windows Form Designer.
        InitializeComponent()
        "Add any initialization after the InitializeComponent() call
    End Sub
    "Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents TextBox2 As System.Windows.Forms.TextBox
    Friend WithEvents Label1 As System.Windows.Forms.Label
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.Button1 = New System.Windows.Forms.Button
        Me.TextBox2 = New System.Windows.Forms.TextBox
        Me.Label1 = New System.Windows.Forms.Label
        Me.SuspendLayout()
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(96, 56)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.PasswordChar = Microsoft.VisualBasic.ChrW(42)
        Me.TextBox1.TabIndex = 0
        Me.TextBox1.Text = ""
        "
        "Button1
        "
        Me.Button1.Location = New System.Drawing.Point(104, 104)
        Me.Button1.Name = "Button1"
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "Read Text"
        "
        "TextBox2
        "
        Me.TextBox2.Location = New System.Drawing.Point(96, 160)
        Me.TextBox2.Name = "TextBox2"
        Me.TextBox2.TabIndex = 2
        Me.TextBox2.Text = ""
        "
        "Label1
        "
        Me.Label1.Font = New System.Drawing.Font("Microsoft Sans Serif", 24.0!, System.Drawing.FontStyle.Regular, System.Drawing.GraphicsUnit.Point, CType(0, Byte))
        Me.Label1.Location = New System.Drawing.Point(0, 0)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(184, 40)
        Me.Label1.TabIndex = 3
        Me.Label1.Text = "Passwords"
        "
        "Form1
        "
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.Add(Me.Label1)
        Me.Controls.Add(Me.TextBox2)
        Me.Controls.Add(Me.Button1)
        Me.Controls.Add(Me.TextBox1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
    End Sub
#End Region
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        TextBox2.Text = TextBox1.Text
    End Sub
End Class

Disable TextBox Context Menu

Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Windows.Forms
public class DisableTextBoxContextMenu
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class
Public Class Form1
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim text_box As New NoCtxMnuTextBox
        text_box.Location = New Point(TextBox1.Left, TextBox1.Top + TextBox1.Height + 4)
        text_box.Size = TextBox1.Size
        Me.Controls.Add(text_box)
    End Sub
End Class
Public Class NoCtxMnuTextBox
    Inherits System.Windows.Forms.TextBox
    Protected Overrides Sub WndProc(ByRef m As System.Windows.Forms.Message)
        Const WM_CONTEXTMENU As Integer = &H7B
        If m.Msg <> WM_CONTEXTMENU Then
            MyBase.WndProc(m)
        End If
    End Sub
End Class
<Global.Microsoft.VisualBasic.rupilerServices.DesignerGenerated()> _
Partial Public Class Form1
    Inherits System.Windows.Forms.Form
    "Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.SuspendLayout()
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(16, 16)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(120, 20)
        Me.TextBox1.TabIndex = 0
        "
        "Form1
        "
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 13.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(156, 102)
        Me.Controls.Add(Me.TextBox1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
        Me.PerformLayout()
    End Sub
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
End Class

Display text file in a TextBox

Imports System.IO
Imports System.Windows.Forms
public class TextFileDisplayTextBox
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class

Public Class Form1
    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
    Public Sub New()
        MyBase.New()
        "This call is required by the Windows Form Designer.
        InitializeComponent()
        "Add any initialization after the InitializeComponent() call
    End Sub
    "Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.TextBox1 = New System.Windows.Forms.TextBox()
        Me.SuspendLayout()
        "
        "Button1
        "
        Me.Button1.Location = New System.Drawing.Point(104, 24)
        Me.Button1.Name = "Button1"
        Me.Button1.TabIndex = 0
        Me.Button1.Text = "Select a File"
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(20, 80)
        Me.TextBox1.Multiline = True
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(250, 150)
        Me.TextBox1.TabIndex = 1
        Me.TextBox1.Text = ""
        "
        "Form1
        "
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.Button1, Me.TextBox1})
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
    End Sub
#End Region
    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim FileDB As New OpenFileDialog()
        FileDB.Filter = "All files | *.* | Word files | *.doc | Text files | *.txt"
        FileDB.FilterIndex = 3
        FileDB.InitialDirectory = "C:\Temp"
        If (FileDB.ShowDialog() = DialogResult.OK) Then
            Dim FS As FileStream
            Try
                FS = FileDB.OpenFile()
            Catch
                MsgBox("Error opening " & FileDB.FileName)
            End Try
            Dim TextData(1025) As Byte
            Dim BytesRead As Integer
            Dim I As Integer
            Dim NewText As String
            Do
                Try
                    BytesRead = FS.Read(TextData, 1, 1024)
                    NewText = ""
                    For I = 1 To BytesRead
                        NewText = NewText & Chr(TextData(I))
                    Next
                    TextBox1.AppendText(NewText)
                Catch
                    MsgBox("Error reading file")
                End Try
            Loop While (BytesRead <> 0)
            FS.Close()
        Else
                MsgBox("User selected Cancel")
        End If
    End Sub
End Class

Get input from TextBox and Set to Label

Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Windows.Forms
public class GetTextInTextBoxAndSetToLabel
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class

Public Class Form1
    Inherits System.Windows.Forms.Form
    Public Sub New()
        MyBase.New()
        InitializeComponent()
    End Sub
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    Private components As System.ruponentModel.IContainer
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Button1 As System.Windows.Forms.Button
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Label1 = New System.Windows.Forms.Label
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.Button1 = New System.Windows.Forms.Button
        Me.SuspendLayout()
        "
        "Label1
        "
        Me.Label1.Location = New System.Drawing.Point(48, 16)
        Me.Label1.Name = "Label1"
        Me.Label1.Size = New System.Drawing.Size(160, 32)
        Me.Label1.TabIndex = 0
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(64, 64)
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(120, 20)
        Me.TextBox1.TabIndex = 1
        Me.TextBox1.Text = ""
        "
        "Button1
        "
        Me.Button1.Location = New System.Drawing.Point(88, 104)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(72, 24)
        Me.Button1.TabIndex = 2
        Me.Button1.Text = "Display"
        "
        "Form1
        "
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(256, 166)
        Me.Controls.Add(Me.Button1)
        Me.Controls.Add(Me.TextBox1)
        Me.Controls.Add(Me.Label1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
    End Sub
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Label1.Text = "Hello," + TextBox1.Text + ""
    End Sub
End Class

Get selected text in TextBox

Imports System.Windows.Forms
Imports System.Drawing.Text
Imports System.Drawing
Imports System.Drawing.Drawing2D
public class TextBoxSelectionLength
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class
Public Class Form1
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        If TextBox1.SelectionLength = 0 Then
            MessageBox.Show(TextBox1.Text)
        Else
            MessageBox.Show(TextBox1.SelectedText)
        End If
    End Sub
End Class
<Global.Microsoft.VisualBasic.rupilerServices.DesignerGenerated()> _
Partial Class Form1
    Inherits System.Windows.Forms.Form
    "Form overrides dispose to clean up the component list.
    <System.Diagnostics.DebuggerNonUserCode()> _
    Protected Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing AndAlso components IsNot Nothing Then
            components.Dispose()
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> _
    Private Sub InitializeComponent()
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.Button1 = New System.Windows.Forms.Button
        Me.SuspendLayout()
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(12, 12)
        Me.TextBox1.Multiline = True
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(410, 137)
        Me.TextBox1.TabIndex = 0
        "
        "Button1
        "
        Me.Button1.Location = New System.Drawing.Point(150, 173)
        Me.Button1.Name = "Button1"
        Me.Button1.Size = New System.Drawing.Size(131, 23)
        Me.Button1.TabIndex = 1
        Me.Button1.Text = "Display selected text"
        Me.Button1.UseVisualStyleBackColor = True
        "
        "Form1
        "
        Me.AutoScaleDimensions = New System.Drawing.SizeF(6.0!, 12.0!)
        Me.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font
        Me.ClientSize = New System.Drawing.Size(434, 208)
        Me.Controls.Add(Me.Button1)
        Me.Controls.Add(Me.TextBox1)
        Me.ResumeLayout(False)
        Me.PerformLayout()
    End Sub
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    Friend WithEvents Button1 As System.Windows.Forms.Button
End Class

Inherit TextBox to create custom control based on TextBox

Imports System
Imports System.Collections
Imports System.IO
Imports System.Windows.Forms
Imports System.Drawing
Imports System.Drawing.Drawing2D
Public Class FileTextBox
    Inherits TextBox
#Region " Component Designer generated code "
    Public Sub New(ByVal Container As System.ruponentModel.IContainer)
        MyClass.New()
        "Required for Windows.Forms Class Composition Designer support
        Container.Add(Me)
    End Sub
    Public Sub New()
        MyBase.New()
        "This call is required by the Component Designer.
        InitializeComponent()
        "Add any initialization after the InitializeComponent() call
    End Sub
    "Component overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Component Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Component Designer
    "It can be modified using the Component Designer.
    "Do not modify it using the code editor.
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        components = New System.ruponentModel.Container()
    End Sub
#End Region

    Protected Overrides Sub OnTextChanged(ByVal e As System.EventArgs)
        If Not File.Exists(Me.Text) Then
            Me.ForeColor = Color.Red
        Else
            Me.ForeColor = Color.Black
        End If
        MyBase.OnTextChanged(e)
    End Sub
End Class

Multiline Text Boxes

Imports System.Drawing
Imports System.Drawing.Drawing2D
Imports System.Windows.Forms
public class TextBoxMultiline
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class
Public Class Form1
    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
    Public Sub New()
        MyBase.New()
        "This call is required by the Windows Form Designer.
        InitializeComponent()
        "Add any initialization after the InitializeComponent() call
    End Sub
    "Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    Friend WithEvents Label1 As System.Windows.Forms.Label
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Label1 = New System.Windows.Forms.Label
        Me.TextBox1 = New System.Windows.Forms.TextBox
        Me.SuspendLayout()
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(5, 5)
        Me.TextBox1.Multiline = True
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.ScrollBars = System.Windows.Forms.ScrollBars.Both
        Me.TextBox1.Size = New System.Drawing.Size(200, 150)
        Me.TextBox1.TabIndex = 2
        Me.TextBox1.Text = ""
        "
        "Form1
        "
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(288, 189)
        Me.Controls.Add(Me.TextBox1)
        Me.Controls.Add(Me.Label1)
        Me.Name = "Form1"
        Me.Text = "Form1"
        Me.ResumeLayout(False)
    End Sub
#End Region
End Class

Numeric TextBox

Imports System.Windows.Forms
public class NumericTextBoxDemo
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class
Public Class Form1
    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
    Public Sub New()
        MyBase.New()
        "This call is required by the Windows Form Designer.
        InitializeComponent()
        "Add any initialization after the InitializeComponent() call
    End Sub
    "Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
   Friend WithEvents Button1 As System.Windows.Forms.Button
   Friend WithEvents NumTextBox1 As NumTextBox
   <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
      Me.Button1 = New System.Windows.Forms.Button()
      Me.NumTextBox1 = New NumTextBox()
      Me.SuspendLayout()
      "
      "Button1
      "
      Me.Button1.Location = New System.Drawing.Point(144, 120)
      Me.Button1.Name = "Button1"
      Me.Button1.TabIndex = 1
      Me.Button1.Text = "Do It!"
      "
      "NumTextBox1
      "
      Me.NumTextBox1.Location = New System.Drawing.Point(32, 56)
      Me.NumTextBox1.Name = "NumTextBox1"
      Me.NumTextBox1.TabIndex = 3
      Me.NumTextBox1.Text = "NumTextBox1"
      "
      "Form1
      "
      Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
      Me.ClientSize = New System.Drawing.Size(292, 266)
      Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.NumTextBox1, Me.Button1})
      Me.Name = "Form1"
      Me.Text = "Form1"
      Me.ResumeLayout(False)
   End Sub
#End Region
   
End Class

Public Class NumTextBox
   Inherits System.Windows.Forms.TextBox
#Region " Windows Form Designer generated code "
   Public Sub New()
      MyBase.New()
      "This call is required by the Windows Form Designer.
      InitializeComponent()
      "Add any initialization after the InitializeComponent() call
   End Sub
   "UserControl1 overrides dispose to clean up the component list.
   Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
      If disposing Then
         If Not (components Is Nothing) Then
            components.Dispose()
         End If
      End If
      MyBase.Dispose(disposing)
   End Sub
   "Required by the Windows Form Designer
   Private components As System.ruponentModel.IContainer
   "NOTE: The following procedure is required by the Windows Form Designer
   "It can be modified using the Windows Form Designer.  
   "Do not modify it using the code editor.
   <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
      "
      "NumTextBox
      "
   End Sub
#End Region
  
   Protected Overrides Sub OnLeave(ByVal e As System.EventArgs)
      If Not IsNumeric(Me.Text) Then
         MessageBox.Show("You must enter a numeric value!", _
            "Please try again....", MessageBoxButtons.OK, _
            MessageBoxIcon.Exclamation)
         Me.Focus()
      End If
      MyBase.OnLeave(e)
   End Sub
End Class

Save text in TextBox to a file

Imports System.IO
Imports System.Windows.Forms
public class SaveTextBoxToFile
   public Shared Sub Main
        Application.Run(New Form1)
   End Sub
End class
Public Class Form1
    Inherits System.Windows.Forms.Form
#Region " Windows Form Designer generated code "
    Public Sub New()
        MyBase.New()
        "This call is required by the Windows Form Designer.
        InitializeComponent()
        "Add any initialization after the InitializeComponent() call
    End Sub
    "Form overrides dispose to clean up the component list.
    Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
        If disposing Then
            If Not (components Is Nothing) Then
                components.Dispose()
            End If
        End If
        MyBase.Dispose(disposing)
    End Sub
    "Required by the Windows Form Designer
    Private components As System.ruponentModel.IContainer
    "NOTE: The following procedure is required by the Windows Form Designer
    "It can be modified using the Windows Form Designer.  
    "Do not modify it using the code editor.
    Friend WithEvents Button1 As System.Windows.Forms.Button
    Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
    <System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
        Me.Button1 = New System.Windows.Forms.Button()
        Me.TextBox1 = New System.Windows.Forms.TextBox()
        Me.SuspendLayout()
        "
        "Button1
        "
        Me.Button1.Location = New System.Drawing.Point(104, 24)
        Me.Button1.Name = "Button1"
        Me.Button1.TabIndex = 0
        Me.Button1.Text = "Save to File"
        "
        "TextBox1
        "
        Me.TextBox1.Location = New System.Drawing.Point(20, 80)
        Me.TextBox1.Multiline = True
        Me.TextBox1.Name = "TextBox1"
        Me.TextBox1.Size = New System.Drawing.Size(250, 150)
        Me.TextBox1.TabIndex = 1
        Me.TextBox1.Text = ""
        "
        "Form1
        "
        Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
        Me.ClientSize = New System.Drawing.Size(292, 273)
        Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.Button1, Me.TextBox1})
        Me.Name = "Form1"
        Me.Text = "SaveTextToFile"
        Me.ResumeLayout(False)
    End Sub
#End Region
    Private Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim FileDB As New SaveFileDialog()
        FileDB.Filter = "All files | *.* | Word files | *.doc | Text files | *.txt"
        FileDB.FilterIndex = 3
        FileDB.InitialDirectory = "C:\Temp"
        FileDB.AddExtension = True
        FileDB.DefaultExt = "txt"
        If (FileDB.ShowDialog() = DialogResult.OK) Then
            Dim FS As FileStream
            Try
                FS = New FileStream(FileDB.FileName, FileMode.Create)
                Dim I As Integer
                For I = 0 To TextBox1.Text.Length - 1
                    FS.WriteByte(Asc(TextBox1.Text.Chars(I)))
                Next
            Catch
                Console.WriteLine("Error writing file")
            End Try
            FS.Close()
            MsgBox("Text saved to " & FileDB.FileName)
        Else
            MsgBox("User selected Cancel")
        End If
    End Sub
End Class

TextBox Text Changed Event

imports System
imports System.Drawing
imports System.Windows.Forms
public class TextBoxTextChanged : inherits Form
  dim txt as TextBox
  dim btn as Button
  dim strOriginal as string
  public sub New()
        Text = "TextBox Modified and TextChanged"
    Size = new Size(300, 375)
    txt = new TextBox()
    txt.Parent = me
    txt.Text = "Enter text here."
    txt.Size = new Size(280, 275)
    txt.Location = new Point(10,10)
    AddHandler txt.TextChanged, AddressOf txt_TextChanged
    txt.Multiline = true
    txt.BorderStyle = BorderStyle.Fixed3D
    txt.ScrollBars = ScrollBars.Vertical
    txt.Anchor = AnchorStyles.Left or AnchorStyles.Right or AnchorStyles.Top or AnchorStyles.Bottom
    strOriginal = txt.Text
    btn = new Button()
    btn.Parent = me
    btn.Text = "Check "
    btn.Location = new Point(20,320)
    AddHandler btn.Click, AddressOf btn_Click
    btn.Anchor = AnchorStyles.Bottom
  end sub
  public shared sub Main() 
    Application.Run(new TextBoxTextChanged())
  end sub
  private sub txt_TextChanged(ByVal sender as object,ByVal e as EventArgs)
    Console.WriteLine("txt_TextChanged")
    if strOriginal = txt.Text then
      txt.Modified = false
    else
      txt.Modified = true
    end if
  end sub
  private sub btn_Click(ByVal sender as object,ByVal e as EventArgs)
    if txt.Modified then
      Console.WriteLine("modified.")
      strOriginal = txt.Text
      txt.Modified = false
    else
      Console.WriteLine("not been modified." )
    end if
  end sub
end class