如何在对象的构造函数完成后立即触发事件？

Question

研究告诉我，从构造函数本身引发事件是不可行的，因为对象可能没有完全初始化...所以我可以在构造函数触发后立即从哪里触发事件？

Answer 1

您可以使用显示的加载或显示事件。

   Private Sub myForm_Shown(sender As Object, e As EventArgs) Handles Me.Shown

   End Sub

或

 Private Sub myForm_Load(sender As Object, e As EventArgs) Handles Me.Load

    End Sub

Answer 2

您可以做的一件事是添加一个方法来处理其他后期任务：

Friend Class FooBar

     Public Sub New
         ' your code here
     End Sub

     Public Sub Create
        ' do anything you want
     End Sub

End Class

其他地方：

Friend WithEvents Foo As Foobar

' ...
Foo = New FooBar      '  Foo doesnt exist until ctor code executes and the
                      ' code returns to here. 

Foo.Create            ' do whatever you like, as long as any other
                      ' objects referenced have been created.               

调用来自ctor的sub来引发一个不能使用类的事件的原因是：

Private Sub SomeEvent(sender As Object, e As EventArgs) Handles Foo.SomeEvent
    Console.Beep()
End Sub

密钥为Handles Foo.SomeEvent

尚未处理此事件的Foo。它没有崩溃并且引发了事件，但是侦听器没有捕获/处理事件的对象。在InitializeComponents中创建了足够的表单，它可以使用表单。

可能还有一个接口来实现这样的东西，我知道一些用于组件，但不是类。

Answer 3

您可以通过向构造函数添加Action(Of T)参数并在最后一行调用委托来完成此操作。

Public Class Foo

    Public Sub New(ByVal action As Action(Of Foo))
        '...
        '...
        '...
        If (Not action Is Nothing) Then action.Invoke(Me)
    End Sub

End Class

示例

Public Class Form1

    Private Sub Button1_Click(sender As Object, ev As EventArgs) Handles Button1.Click
        Dim foo1 As New Foo("foo1", AddressOf Me.HandleFooCtor)
        Dim foo2 As New Foo("foo2", Sub(f As Foo) MessageBox.Show(f.Name))
    End Sub

    Private Sub HandleFooCtor(f As Foo)
        MessageBox.Show(f.Name)
    End Sub

    Public Class Foo

        Public Sub New(name As String, Optional ByVal action As Action(Of Foo) = Nothing)
            '...
            '...
            '...
            Me.Name = name
            If (Not action Is Nothing) Then action.Invoke(Me)
        End Sub

        Public ReadOnly Name As String

    End Class

End Class