vb.net - KeyDown 事件未通过 .NET WinForms 触发？

Question

我已经 KeyPreview 在表单属性中设置为 true

我正在开发一个小程序，我遇到了一个问题，当我按下并释放任何箭头键时，组框中的某些控件似乎没有触发表单上的 KeyDown 事件，只是KeyUp 事件。我的代码是否有问题可能导致此问题？

具体来说，我在表单上启用了 KeyPreview，并在两个子例程中的 e.SuppressKeyPress = True 上设置了断点，只有 frmMain_KeyUp 的那个子例程命中了断点。

我添加了两个 GroupBox 事件，希望可以缓解这个问题，但没有那么幸运。但是，我在表单上有一个自定义控件，该控件经过专门编码以忽略这些按键，并且代码按预期工作。

  Private Sub frmMain_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown, GroupBox1.KeyDown, GroupBox2.KeyDown
      e.SuppressKeyPress = True
      Select Case e.KeyCode
          Case Keys.Left
              ScrollDir = ScrollDir Or 1
          Case Keys.Right
              ScrollDir = ScrollDir Or 2
          Case Keys.Down
              ScrollDir = ScrollDir Or 4
          Case Keys.Up
              ScrollDir = ScrollDir Or 8
          Case Else
              e.SuppressKeyPress = False
      End Select
      tScroll.Enabled = True
      tScroll_Tick(Nothing, Nothing)
  End Sub

  Private Sub frmMain_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyUp, GroupBox1.KeyUp, GroupBox2.KeyUp

      e.SuppressKeyPress = True
      Select Case e.KeyCode
          Case Keys.Left
              ScrollDir = ScrollDir And (Not 1)
          Case Keys.Right
              ScrollDir = ScrollDir And (Not 2)
          Case Keys.Down
              ScrollDir = ScrollDir And (Not 4)
          Case Keys.Up
              ScrollDir = ScrollDir And (Not 8)
          Case Else
              e.SuppressKeyPress = False
      End Select
      If ScrollDir = 0 Then tScroll.Enabled = False
  End Sub

用户控件中“忽略”按键的代码如下:

    Private Sub TileDropDown_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyDown
        If e.KeyValue = 40 OrElse e.KeyValue = 38 OrElse e.KeyValue = 39 OrElse e.KeyValue = 37 Then

            e.SuppressKeyPress = True
        End If
    End Sub

Answer 1

某些控件会在 keydown 事件中拦截箭头键，但不会在 keyup 事件中拦截箭头键。一种解决方案是派生控件类并重写 ProcessCmdKey:

Protected Overrides Function ProcessCmdKey(ByRef msg As Message, ByVal keydata As Keys) As Boolean

If keydata = Keys.Right Or keydata = Keys.Left Or keydata = Keys.Up Or keydata = Keys.Down Then
  OnKeyDown(New KeyEventArgs(keydata))
  ProcessCmdKey = True
Else
  ProcessCmdKey = MyBase.ProcessCmdKey(msg, keydata)
  End If
End Function