Question

在C＃中，您可以在add订阅/取消订阅时定义明确的remove / event代码。

这在VB.net中是否可行？

Answer 1

Imports System.Runtime.CompilerServices
...
    Private propchanged As PropertyChangedEventHandler

    Public Custom Event PropertyChanged As PropertyChangedEventHandler

        <MethodImpl(MethodImplOptions.Synchronized)> _
        AddHandler(ByVal value As PropertyChangedEventHandler)
            propchanged = DirectCast([Delegate].Combine(propchanged, value), PropertyChangedEventHandler)
        End AddHandler

        <MethodImpl(MethodImplOptions.Synchronized)> _
        RemoveHandler(ByVal value As PropertyChangedEventHandler)
            propchanged = DirectCast([Delegate].Remove(propchanged, value), PropertyChangedEventHandler)
        End RemoveHandler

        RaiseEvent(ByVal sender As Object, ByVal e As System.ComponentModel.PropertyChangedEventArgs)
            Dim handler = propchanged
            If handler IsNot Nothing Then handler(sender, e)
        End RaiseEvent
    End Event

Answer 2

看起来可以使用定义here的自定义事件来完成。

  ' Define the MouseDown event property.
    Public Custom Event MouseDown As MouseEventHandler
        ' Add the input delegate to the collection.
        AddHandler(Value As MouseEventHandler)
            listEventDelegates.AddHandler(mouseDownEventKey, Value)
        End AddHandler
        ' Remove the input delegate from the collection.
        RemoveHandler(Value As MouseEventHandler)
            listEventDelegates.RemoveHandler(mouseDownEventKey, Value)
        End RemoveHandler
        ' Raise the event with the delegate specified by mouseDownEventKey
        RaiseEvent(sender As Object, e As MouseEventArgs)
            Dim mouseEventDelegate As MouseEventHandler = _
                listEventDelegates(mouseDownEventKey)
            mouseEventDelegate(sender, e)
        End RaiseEvent
    End Event

在VB.net中显式添加/删除事件

2 个答案: