.NET WinForms中的KeyDown事件为什么不触发？

Question

我已经在窗体属性中将KeyPreview设置为true

我正在开发一个小程序，但是当我按下并释放任何箭头键时，它似乎有些控件（位于GroupBox内）没有触发窗体的KeyDown事件，只触发了KeyUp事件。是否我的代码有问题导致这种情况发生？

具体地说，我已经在窗体上启用了KeyPreview，并在两个子例程的e.SuppressKeyPress = True处设置了断点，只有frmMain_KeyUp的那个例程触发了断点。

我添加了两个GroupBox事件，希望这可以缓解问题，但没有这样的运气。但是，我在窗体上有一个自定义控件，专门编写了忽略这些按键的代码，该代码按预期工作。

  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

在用户控件中“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

- Sukasa

---

在忽略控件的代码中设置一个断点，看它是否至少触发一次。 - curtisk

在frmMain的KeyDown处理程序中取消注释e.SuppressKeyPress = True后，TileDropDown_KeyDown子例程将不会被调用。如果将其注释掉，则处理程序会被调用。 - Sukasa

Answer 1

有些控件会在keydown事件中截获方向键，但不会在keyup事件中截获。一个解决办法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

- xpda

Answer 2

在vb.net中处理箭头键，加载函数中使用Me.KeyPreview = True，目标函数中使用(Handles Me.KeyUp)即可，不需要做太多操作。

- user10146953