拖放取消

Question

我有一个包含 2 个面板的表格：
Panel1.BackColor 为 Color.Red
Panel2.BackColor为Color.Blue

将 panel1 拖到 panel2 时，panel2 必须采用 panel1 的颜色
启动拖动操作面板1时必须将颜色更改为白色
拖放完成后，panel1 必须返回红色。

这一切都完成了，但我还是怀念这个：
如果取消拖放操作（在其他控件上拖放、按 ESC 等），则 panel2 的颜色保持白色，不会恢复为 Color.Red。

我该如何实现这个目标？

我尝试查看 QueryContinueDrag，但似乎找不到解决方案。

这是我的代码：

Public Class Form1

    Private dragBoxFromMouseDown As Rectangle

    Private Sub Panel1_MouseDown(sender As Object, e As MouseEventArgs) Handles Panel1.MouseDown
        Dim dragSize As Size = SystemInformation.DragSize
        dragBoxFromMouseDown = New Rectangle(New Point(e.X - (dragSize.Width / 2), e.Y - (dragSize.Height / 2)), dragSize)
    End Sub

    Private Sub Panel1_MouseMove(sender As Object, e As MouseEventArgs) Handles Panel1.MouseMove
        If ((e.Button And MouseButtons.Left) = MouseButtons.Left) Then
            If (Rectangle.op_Inequality(dragBoxFromMouseDown, Rectangle.Empty) And Not dragBoxFromMouseDown.Contains(e.X, e.Y)) Then
                Panel1.BackColor = Color.White
                Panel1.DoDragDrop(sender.name, DragDropEffects.All)

            End If
        End If
    End Sub

    Private Sub Panel2_DragEnter(ByVal sender As Object, ByVal e As System.Windows.Forms.DragEventArgs) Handles Panel2.DragEnter
        If e.Data.GetData(DataFormats.Text).contains("Panel1") Then
            e.Effect = DragDropEffects.Copy
        End If
    End Sub

    Private Sub Panel2_DragDrop(sender As Object, e As DragEventArgs) Handles Panel2.DragDrop
        Panel2.BackColor = Me.Controls(e.Data.GetData(DataFormats.Text)).backcolor
        Me.Controls(e.Data.GetData(DataFormats.Text)).backcolor = Color.Red
    End Sub
End Class

Answer 1

正如您所提到的，您应该处理源面板的 QueryContinueDrag 事件，以确定正在执行什么操作。可能是

Continue

、

Drop

或

Cancel

。
您想要在当前操作为

DragAction.Drop

或

DragAction.Cancel

时恢复源控件的背景颜色。

我重构了这里提供的一些代码，因为它包含一些奇怪的东西。
例如，您可以简单地将 Control 实例传递给

DoDragDrop()

方法，然后使用

e.Data.GetDataPresent()

验证它是否包含您要处理的 Type。
另外，缺少一些空检查

Private panelQueryDragPosition As Point
Private Sub Panel1_MouseDown(sender As Object, e As MouseEventArgs) Handles Panel1.MouseDown
    panelQueryDragPosition = e.Location
End Sub

Private Sub Panel1_MouseMove(sender As Object, e As MouseEventArgs) Handles Panel1.MouseMove
    If e.Button = MouseButtons.Left AndAlso
        (Math.Abs(e.X - panelQueryDragPosition.X) > SystemInformation.DragSize.Width OrElse
         Math.Abs(e.Y - panelQueryDragPosition.Y) > SystemInformation.DragSize.Height) Then
        Dim ctl = DirectCast(sender, Panel)  ' The source Control cannot be null here
        ctl.BackColor = Color.White
        ctl.DoDragDrop(ctl, DragDropEffects.Copy)
    End If
End Sub

Private Sub Panel1_QueryContinueDrag(sender As Object, e As QueryContinueDragEventArgs) Handles Panel1.QueryContinueDrag
    If e.Action = DragAction.Drop OrElse e.Action = DragAction.Cancel Then
        Dim ctl = DirectCast(sender, Control)
        If ctl IsNot Nothing Then ctl.BackColor = Color.Red
    End If
End Sub

Private Sub Panel2_DragEnter(sender As Object, e As DragEventArgs) Handles Panel2.DragEnter
    If e.Data IsNot Nothing AndAlso e.Data.GetDataPresent(GetType(Panel)) Then
        e.Effect = DragDropEffects.Copy
    Else
        e.Effect = DragDropEffects.None
    End If
End Sub

Private Sub Panel2_DragDrop(sender As Object, e As DragEventArgs) Handles Panel2.DragDrop
    Dim panel = DirectCast(sender, Panel)
    If panel IsNot Nothing AndAlso e.Data IsNot Nothing AndAlso e.Data.GetDataPresent(GetType(Panel)) Then
        Dim sourceControl = DirectCast(e.Data.GetData(GetType(Panel)), Panel)
        panel.BackColor = sourceControl.BackColor
    End If
End Sub