多線程中用委托，不會(huì)沖突。
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在類中用委托，也可以方便模塊思路。
委托主要用于.NETFramework中的事件處理程序和回調(diào)函數(shù)，它是事件的基礎(chǔ)。委托的作用類似于c++中函數(shù)指針的作用。不同的是，委托實(shí)例獨(dú)立于它所封裝的方法的類，并且方法類型與委托的類型是兼容的。函數(shù)指針只能引用靜態(tài)函數(shù)，而委托可以應(yīng)用靜態(tài)和實(shí)例方法。所有委托都是繼承自System.Delegate類，并且有一個(gè)調(diào)用列表。調(diào)用委托時(shí)所執(zhí)行的方法都被存放在這樣的一個(gè)連接列表中。使用delegate關(guān)鍵字可以聲明一個(gè)委托。通過(guò)將委托與命名方法或匿名方法關(guān)聯(lián)，可以對(duì)委托進(jìn)行實(shí)例化。為了與命名方法一起使用，委托必須用具有可接受簽名的方法進(jìn)行實(shí)例化。usingSystem;usingSystem.Collections.Generic;usingSystem.Linq;usingSystem.Text;namespaceConsoleApplication1{//聲明一個(gè)委托delegateintMydelegate();classProgram{staticvoidMain(string[]args){testp=newtest();//將委托指向非靜態(tài)方法Mydelegatem=newMydelegate(p.InstanceMethod);//調(diào)用非靜態(tài)方法m();//將委托指向靜態(tài)方法m=newMydelegate(test.StaticMethod);//調(diào)用靜態(tài)方法m();Console.Read();}}publicclasstest{publicintInstanceMethod(){Console.WriteLine("正在調(diào)用非靜態(tài)方法InstanceMethod().");return0;}staticpublicintStaticMethod(){Console.WriteLine("正在調(diào)用靜態(tài)方法StaticMethod（）。。。。");return0;}}}
一委托：此示例演示如何將方法與委托關(guān)聯(lián)然后通過(guò)委托調(diào)用該方法。
創(chuàng)建委托和匹配過(guò)程
創(chuàng)建一個(gè)名為 MySubDelegate 的委托。
Delegate Sub MySubDelegate(ByVal x As Integer)
聲明一個(gè)類，該類包含與該委托具有相同簽名的方法。
Class class1
Sub Sub1(ByVal x As Integer)
MsgBox("The value of x is: " CStr(x))
End Sub
End Class
定義一個(gè)方法，該方法創(chuàng)建該委托的實(shí)例并通過(guò)調(diào)用內(nèi)置的 Invoke 方法調(diào)用與該委托關(guān)聯(lián)的方法。
Protected Sub DelegateTest()
Dim c1 As New class1
' Create an instance of the delegate.
Dim msd As MySubDelegate = AddressOf c1.Sub1
' Call the method.
msd.Invoke(10)
End Sub
二、事件
下面的示例程序闡釋如何在一個(gè)類中引發(fā)一個(gè)事件，然后在另一個(gè)類中處理該事件。AlarmClock 類定義公共事件 Alarm，并提供引發(fā)該事件的方法。AlarmEventArgs 類派生自 EventArgs，并定義 Alarm 事件特定的數(shù)據(jù)。WakeMeUp 類定義處理 Alarm 事件的 AlarmRang 方法。AlarmDriver 類一起使用類，將使用 WakeMeUp 的 AlarmRang 方法設(shè)置為處理 AlarmClock 的 Alarm 事件。
該示例程序使用事件和委托和引發(fā)事件中詳細(xì)說(shuō)明的概念。
示例
' EventSample.vb.
'
Option Explicit
Option Strict
Imports System
Imports System.ComponentModel
Imports Microsoft.VisualBasic
Namespace EventSample
' Class that contains the data for
' the alarm event. Derives from System.EventArgs.
'
Public Class AlarmEventArgs
Inherits EventArgs
Private _snoozePressed As Boolean
Private nrings As Integer
'Constructor.
'
Public Sub New(snoozePressed As Boolean, nrings As Integer)
Me._snoozePressed = snoozePressed
Me.nrings = nrings
End Sub
' The NumRings property returns the number of rings
' that the alarm clock has sounded when the alarm event
' is generated.
'
Public ReadOnly Property NumRings() As Integer
Get
Return nrings
End Get
End Property
' The SnoozePressed property indicates whether the snooze
' button is pressed on the alarm when the alarm event is generated.
'
Public ReadOnly Property SnoozePressed() As Boolean
Get
Return _snoozePressed
End Get
End Property
' The AlarmText property that contains the wake-up message.
'
Public ReadOnly Property AlarmText() As String
Get
If _snoozePressed Then
Return "Wake Up!!! Snooze time is over."
Else
Return "Wake Up!"
End If
End Get
End Property
End Class
' Delegate declaration.
'
Public Delegate Sub AlarmEventHandler(sender As Object, _
e As AlarmEventArgs)
' The Alarm class that raises the alarm event.
'
Public Class AlarmClock
Private _snoozePressed As Boolean = False
Private nrings As Integer = 0
Private stopFlag As Boolean = False
' The Stop property indicates whether the
' alarm should be turned off.
'
Public Property [Stop]() As Boolean
Get
Return stopFlag
End Get
Set
stopFlag = value
End Set
End Property
' The SnoozePressed property indicates whether the snooze
' button is pressed on the alarm when the alarm event is generated.
'
Public Property SnoozePressed() As Boolean
Get
Return _snoozePressed
End Get
Set
_snoozePressed = value
End Set
End Property
' The event member that is of type AlarmEventHandler.
'
Public Event Alarm As AlarmEventHandler
' The protected OnAlarm method raises the event by invoking
' the delegates. The sender is always this, the current instance
' of the class.
'
Protected Overridable Sub OnAlarm(e As AlarmEventArgs)
RaiseEvent Alarm(Me, e)
End Sub
' This alarm clock does not have
' a user interface.
' To simulate the alarm mechanism it has a loop
' that raises the alarm event at every iteration
' with a time delay of 300 milliseconds,
' if snooze is not pressed. If snooze is pressed,
' the time delay is 1000 milliseconds.
'
Public Sub Start()
Do
nrings += 1
If stopFlag Then
Exit Do
Else
If _snoozePressed Then
System.Threading.Thread.Sleep(1000)
If (True) Then
Dim e As New AlarmEventArgs(_snoozePressed, nrings)
OnAlarm(e)
End If
Else
System.Threading.Thread.Sleep(300)
Dim e As New AlarmEventArgs(_snoozePressed, nrings)
OnAlarm(e)
End If
End If
Loop
End Sub
End Class
' The WakeMeUp class has a method AlarmRang that handles the
' alarm event.
'
Public Class WakeMeUp
Public Sub AlarmRang(sender As Object, e As AlarmEventArgs)
Console.WriteLine((e.AlarmText + ControlChars.Cr))
If Not e.SnoozePressed Then
If e.NumRings Mod 10 = 0 Then
Console.WriteLine(" Let alarm ring? Enter Y")
Console.WriteLine(" Press Snooze? Enter N")
Console.WriteLine(" Stop Alarm? Enter Q")
Dim input As String = Console.ReadLine()
If input.Equals("Y") Or input.Equals("y") Then
Return
Else
If input.Equals("N") Or input.Equals("n") Then
CType(sender, AlarmClock).SnoozePressed = True
Return
Else
CType(sender, AlarmClock).Stop = True
Return
End If
End If
End If
Else
Console.WriteLine(" Let alarm ring? Enter Y")
Console.WriteLine(" Stop Alarm? Enter Q")
Dim input As String = Console.ReadLine()
If input.Equals("Y") Or input.Equals("y") Then
Return
Else
CType(sender, AlarmClock).Stop = True
Return
End If
End If
End Sub
End Class
' The driver class that hooks up the event handling method of
' WakeMeUp to the alarm event of an Alarm object using a delegate.
' In a forms-based application, the driver class is the
' form.
'
Public Class AlarmDriver
Public Shared Sub Main()
' Instantiates the event receiver.
Dim w As New WakeMeUp()
' Instantiates the event source.
Dim clock As New AlarmClock()
' Wires the AlarmRang method to the Alarm event.
AddHandler clock.Alarm, AddressOf w.AlarmRang
clock.Start()
End Sub
End Class
End Namespace
委托三個(gè)步驟
1、聲明委托 用Delegate 聲明一個(gè)委托 類型 參數(shù)要和 被委托的方法一樣 例如 Delegate Function a(byval x as string) as string
2、實(shí)例化委托 dim t as new a(AddressOf Function Name)
3.通過(guò) t(參數(shù)) 或者 t.Invoke(參數(shù)調(diào)用委托)
示例：
Module module1
Delegate Function a(ByVal x As Integer, ByVal y As Integer) As Integer '聲明委托類型 委托可以使一個(gè)對(duì)象調(diào)用另一個(gè)對(duì)象的方法
Function sum(ByVal x As Integer, ByVal y As Integer) As Integer
Return (x + y)
End Function
Sub main()
Dim d As New a(AddressOf sum) '實(shí)例化委托
Dim s = 0
s = d.Invoke(1, 2) '執(zhí)行委托
Console.WriteLine(s.ToString())
s = d(1, 2) '執(zhí)行委托
Console.WriteLine(s.ToString())
MsgBox("")
End Sub
End Module
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