vb.net声明事件的两种方式

Handles 关键字和 AddHandler 语句都允许您指定特定过程处理特定事件，但存在差异。定义过程时请使用 Handles 关键字以指定该过程处理特定事件。AddHandler 语句在运行时将过程连接到事件。（摘自MSDN）

（1）

Public Class ContainerClass ' Module or class level declaration. WithEvents Obj As New Class1 '和Handles关联 Public Class Class1 ' Declare an event. Public Event Ev_Event() Sub CauseSomeEvent() ' Raise an event. RaiseEvent Ev_Event() End Sub End Class Sub EventHandler() Handles Obj.Ev_Event ' Handle the event. MsgBox("EventHandler caught event.") End Sub ' Call the TestEvents procedure from an instance of the ContainerClass ' class to test the Ev_Event event and the event handler. Public Sub TestEvents() Obj.CauseSomeEvent() End Sub End Class

（2）

Sub TestEvents() Dim Obj As New Class1 ' Associate an event handler with an event. AddHandler Obj.Ev_Event,AddressOf EventHandler ' Call the method to raise the event. Obj.CauseSomeEvent() ' Stop handling events. RemoveHandler Obj.Ev_Event,AddressOf EventHandler ' This event will not be handled. Obj.CauseSomeEvent() End Sub Sub EventHandler() ' Handle the event. MsgBox("EventHandler caught event.") End Sub Public Class Class1 ' Declare an event. Public Event Ev_Event() Sub CauseSomeEvent() ' Raise an event. RaiseEvent Ev_Event() End Sub End Class

实例：

CustomerEventArgs.vb: Public Class CustomerEventArgs Inherits System.EventArgs Private m_name As String Private m_age As Integer Public Sub New() End Sub Public Sub New(ByVal _name As String,ByVal _age As Integer) Me.Name = _name Me.Age = _age End Sub Public Property Name() As String Get Return m_name End Get Set(ByVal value As String) m_name = value End Set End Property Public Property Age() As Integer Get Return m_age End Get Set(ByVal value As Integer) m_age = value End Set End Property End Class Employee.vb Public Class Employee Public Event PlayGame(ByVal sender As Object,ByVal e As CustomerEventArgs) Dim cea As New CustomerEventArgs("zhang",20) Public Sub Game() RaiseEvent PlayGame(Me,cea) End Sub End Class Admin.vb: Public Class Admin 'Notify()和事件Employee.PlayGame的签名相同 Public Sub Notify(ByVal sender As Object,ByVal e As CustomerEventArgs) MessageBox.Show(e.Name & ":" & e.Age.ToString() & "is playing game!") End Sub End Class FormEvent.vb '此窗体上有两个按钮Button1（添加事件），Button2（取消事件） Public Class FormEvent '注释部分为添加事件的第二种方法 Dim emp As New Employee() 'Dim WithEvents eventEmp As New Employee() ‘由Handles处理 Dim ad As New Admin() Private Sub Button1_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button1.Click 'eventEmp.Game() AddHandler emp.PlayGame,AddressOf ad.Notify emp.Game() End Sub '该过程的签名必须与 eventlist 中各事件的签名相匹配 'Private Sub emp_PlayGame(ByVal sender As Object,ByVal e As CustomerEventArgs) Handles eventEmp.PlayGame ' ad.Notify(sender,e) 'End Sub Private Sub Button2_Click(ByVal sender As System.Object,ByVal e As System.EventArgs) Handles Button2.Click RemoveHandler emp.PlayGame,AddressOf ad.Notify End Sub End Class

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