VB.Net/Data Structure/Collection
Содержание
Database Connection state change event
<source lang="vbnet"> Imports System Imports System.Data Imports System.Data.SqlClient
public class MainClass
Shared Sub Main()
Dim thisConnection As New SqlConnection("server=(local)\SQLEXPRESS;" & _
"integrated security=sspi;database=MyDatabase")
" Sql Query
Dim sql As String = "SELECT FirstName, LastName From Employee"
" Create command
Dim thisCommand As New SqlCommand(sql, thisConnection)
" Add second handler to StateChange event
AddHandler thisConnection.StateChange, AddressOf StateIsChanged
Try
" Open connection and fire two statechange events
thisConnection.Open()
" Create datareader
Dim thisReader As SqlDataReader = thisCommand.ExecuteReader()
" Display rows in event log
While thisReader.Read()
Console.WriteLine(thisReader.GetString(0) _
+ "-" + thisReader.GetString(1))
End While
Catch ex As SqlException
Console.WriteLine(ex.Message)
Finally
" Remove second handler from StateChange event
RemoveHandler thisConnection.StateChange, AddressOf StateIsChanged
" Close connection and fire one StateChange event
thisConnection.Close()
End Try
End Sub
Shared Private Sub StateIsChanged(ByVal sender As Object, ByVal e As System.Data.StateChangeEventArgs)
" Event handler for the StateChange Event
Console.WriteLine("Entering Second StateChange EventHandler")
Console.WriteLine("Sender = " + sender.ToString())
Console.WriteLine("Original State = " + e.OriginalState.ToString())
Console.WriteLine("Current State = " + e.CurrentState.ToString())
Console.WriteLine("Exiting Second StateChange EventHandler")
End Sub
End Class
</source>
Do While loop through a Collection
<source lang="vbnet"> Imports System Imports System.Collections Public Class MainClass
Shared Sub Main(ByVal args As String())
Dim m_Employees As New Collection
m_Employees.Add(New Employee("A"))
m_Employees.Add(New Manager("B"))
m_Employees.Add(New Manager("C"))
m_Employees.Add(New Employee("D"))
Dim emp As Employee
Dim employee_enumerator As IEnumerator
employee_enumerator = m_Employees.GetEnumerator()
Do While (employee_enumerator.MoveNext)
emp = CType(employee_enumerator.Current, Employee)
Console.WriteLine( emp.Name )
Loop
End Sub
End Class
Public Class Employee
Public Name As String
Public Sub New(ByVal new_name As String)
Name = new_name
End Sub
Public Overridable Function IsManager() As Boolean
Return False
End Function
End Class Public Class Customer
Public Name As String
Public Sub New(ByVal new_name As String)
Name = new_name
End Sub
End Class Public Class Manager
Inherits Employee
Public Sub New(ByVal new_name As String)
MyBase.new(new_name)
End Sub
Public Overrides Function IsManager() As Boolean
Return True
End Function
End Class
</source>
For Each loop through a Collection
<source lang="vbnet"> Imports System Imports System.Collections Public Class MainClass
Shared Sub Main(ByVal args As String())
Dim people As New Collection
people.Add(New Employee("A"))
people.Add(New Customer("B"))
" Works.
For Each person As Object In people
Console.WriteLine(person.Name)
Next person
End Sub
End Class
Public Class Employee
Public Name As String
Public Sub New(ByVal new_name As String)
Name = new_name
End Sub
Public Overridable Function IsManager() As Boolean
Return False
End Function
End Class Public Class Customer
Public Name As String
Public Sub New(ByVal new_name As String)
Name = new_name
End Sub
End Class Public Class Manager
Inherits Employee
Public Sub New(ByVal new_name As String)
MyBase.new(new_name)
End Sub
Public Overrides Function IsManager() As Boolean
Return True
End Function
End Class
</source>
Loop through Collection
<source lang="vbnet"> Imports System Imports System.Collections Public Class MainClass
Shared Sub Main(ByVal args As String())
Dim m_employees As New Collection
m_employees.Add(New employee("A", "B", "Author"))
m_employees.Add(New employee("C", "D", "Band"))
m_employees.Add(New employee("E", "F", "Artist"))
" Iterator.
Dim emp As employee
Dim employee_enumerator As IEnumerator
employee_enumerator = m_employees.GetEnumerator()
Do While (employee_enumerator.MoveNext)
emp = CType(employee_enumerator.Current, Employee)
Console.WriteLine(emp.Title & " " & emp.FirstName & " " & emp.LastName)
Loop
" For Each.
For Each emp1 As employee In m_employees
Console.WriteLine(emp1.Title & " " & emp1.FirstName & " " & emp1.LastName)
Next emp1
End Sub
End Class
Public Class Employee
Public FirstName As String
Public LastName As String
Public Title As String
Public Sub New(ByVal first_name As String, ByVal last_name As String, ByVal new_title As String)
FirstName = first_name
LastName = last_name
Title = new_title
End Sub
End Class
</source>
Store Class in a Collection and Retrieve by Name
<source lang="vbnet"> Imports System Imports System.Collections
Public Class MainClass
Shared Sub Main(ByVal args As String())
Dim intCollection As New Collection( )
Dim empCollection As New Collection( )
Dim empCollection2 As New Collection( )
" populate the Collections
Dim i As Integer
For i = 0 To 4
empCollection.Add(New EnumerableClass("A", "B"))
intCollection.Add((i * 5))
Next i
" add key/value pairs
empCollection2.Add(New EnumerableClass("A", "B"), "A B")
empCollection2.Add(New EnumerableClass("C", "D"), "C D")
empCollection2.Add(New EnumerableClass("E", "F"), "E F")
" print each member of the array
For Each i In intCollection
Console.Write("{0} ", i.ToString( ))
Next i
Console.WriteLine( )
Console.WriteLine("Employee collection...")
Dim e As EnumerableClass
For Each e In empCollection
Console.Write("{0} ", e.ToString( ))
Next e
Console.WriteLine( )
Console.WriteLine("Employee collection 2...")
For Each e In empCollection2
Console.Write("{0} ", e.ToString( ))
Next e
Console.WriteLine( )
" retrieve an Employee by key
Dim emp As EnumerableClass
emp = empCollection2.Item("A B")
Console.WriteLine( _
" empID {0}", emp.ToString( ))
" note that indexing is 1-based (rather than zero based)
emp = empCollection2.Item(1)
Console.WriteLine( _
"Index(1) retrieved empID {0}", emp.ToString( ))
End Sub
End Class
Public Class EnumerableClass : Implements IEnumerable
Private strings( ) As String
Private ctr As Integer = 0
Private Class MyEnumerator
Implements IEnumerator
Private currentListBox As EnumerableClass
Private index As Integer
Public Sub New(ByVal currentListBox As EnumerableClass)
Me.currentListBox = currentListBox
index = -1
End Sub
Public Function MoveNext( ) As Boolean _
Implements IEnumerator.MoveNext
index += 1
If index >= currentListBox.strings.Length Then
Return False
Else
Return True
End If
End Function
Public Sub Reset( ) _
Implements IEnumerator.Reset
index = -1
End Sub
Public ReadOnly Property Current( ) As Object _
Implements IEnumerator.Current
Get
Return currentListBox(index)
End Get
End Property
End Class " end nested class
Public Function GetEnumerator( ) As IEnumerator _
Implements IEnumerable.GetEnumerator
Return New MyEnumerator(Me)
End Function
Public Sub New( _
ByVal ParamArray initialStrings( ) As String)
ReDim strings(7)
Dim s As String
For Each s In initialStrings
strings(ctr) = s
ctr += 1
Next
End Sub
Public Sub Add(ByVal theString As String)
strings(ctr) = theString
ctr += 1
End Sub
Default Public Property Item( _
ByVal index As Integer) As String
Get
If index < 0 Or index >= strings.Length Then
" handle bad index
Exit Property
End If
Return strings(index)
End Get
Set(ByVal Value As String)
strings(index) = Value
End Set
End Property
Public Function GetNumEntries( ) As Integer
Return ctr
End Function
End Class
</source>
Store Objects in Collection and retrieve
<source lang="vbnet"> Imports System Imports System.Collections Public Class MainClass
Shared Sub Main()
Dim intCollection As New Collection( )
Dim empCollection As New Collection( )
Dim empCollection2 As New Collection( )
"populate the Collections
Dim i As Integer
For i = 0 To 4
empCollection.Add(New Employee(i + 100))
intCollection.Add((i * 5))
Next i
"add key/value pairs
empCollection2.Add(New Employee(1989), "G W")
empCollection2.Add(New Employee(1997), "J A")
empCollection2.Add(New Employee(1901), "T J")
"print each member of the array
For Each i In intCollection
Console.Write("{0} ", i.ToString( ))
Next i
Console.WriteLine( )
Console.WriteLine("Employee collection...")
Dim e As Employee
For Each e In empCollection
Console.Write("{0} ", e.ToString( ))
Next e
Console.WriteLine( )
Console.WriteLine("Employee collection 2...")
For Each e In empCollection2
Console.Write("{0} ", e.ToString( ))
Next e
Console.WriteLine( )
"retrieve an Employee by key
Dim emp As Employee
emp = empCollection2.Item("J A")
Console.WriteLine( emp.ToString( ))
"note that indexing is 1-based (rather than zero based)
emp = empCollection2.Item(1)
Console.WriteLine(emp.ToString( ))
End Sub
End Class
Public Class Employee
Private myEmpID As Integer
Public Sub New(ByVal empID As Integer)
Me.myEmpID = empID
End Sub "New
Public Overrides Function ToString( ) As String
Return myEmpID.ToString( )
End Function "ToString
Public Property EmpID( ) As Integer
Get
Return myEmpID
End Get
Set(ByVal Value As Integer)
myEmpID = Value
End Set
End Property
End Class "Employee
</source>
