WPF 使用 Dispatcher 强制 UI 更新

Question

我只需要显示一个自定义控件（带有旋转指针的时钟）并用它来替换鼠标光标，问题是如果我写：

Me.gridScreen.Visibility = Visibility.Visible
' some operations that takes about 1 second
Me.gridScreen.Visibility = Visibility.Hidden
(gridScreen is the grid that contains the user-control)

显然我什么也看不到，因为 UI 的更新发生在程序结束时。我已经尝试过 Me.UpdateLayout()，但它不起作用。

我尝试过以多种方式使用拆包器，但都没有用 :-(

这是我失败的尝试：

（uCurClock是用户控件，gridScreen是一个放置在窗口顶层的Grid，背景透明，包含用户控件）

Private Sub showClock()
    Dim thread = New System.Threading.Thread(AddressOf showClockIntermediate)
    thread.Start()
End Sub

Private Sub hideClock()
    Dim thread = New System.Threading.Thread(AddressOf hideClockIntermediate)
    thread.Start()
End Sub

Private Sub showClockIntermediate()
    Me.Dispatcher.BeginInvoke(DispatcherPriority.Normal, _
        New Action(AddressOf showClockFinale))
End Sub

Private Sub hideClockIntermediate()
    Me.Dispatcher.BeginInvoke(DispatcherPriority.Normal, _
        New Action(AddressOf hideClockFinale))
End Sub

Private Sub showClockFinale()
    Dim pt As Point = Mouse.GetPosition(Nothing)
    Me.uCurClock.Margin = New Thickness(pt.X - 9, pt.Y - 9, 0, 0)
    Me.gridScreen.Visibility = Visibility.Visible
    Me.Cursor = Cursors.None
    Me.UpdateLayout()
End Sub

Private Sub hideClockFinale()
    Me.gridScreen.Visibility = Visibility.Hidden
    Me.Cursor = Cursors.Arrow
    Me.UpdateLayout()
End Sub

Private Sub u_MouseMove(ByVal sender As System.Object, _
    ByVal e As MouseEventArgs) Handles gridScreen.MouseMove

    Dim pt As Point = e.GetPosition(Nothing)
    Me.uCurClock.Margin = New Thickness(pt.X - 9, pt.Y - 9, 0, 0)

    e.Handled = True
End Sub

Private Sub u_MouseEnter(ByVal sender As System.Object, _
    ByVal e As MouseEventArgs) Handles gridScreen.MouseEnter

    Me.uCurClock.Visibility = Visibility.Visible

    e.Handled = True
End Sub

Private Sub u_MouseLeave(ByVal sender As System.Object, _
    ByVal e As MouseEventArgs) Handles gridScreen.MouseLeave

    Me.uCurClock.Visibility = Visibility.Hidden

    e.Handled = True
End Sub

皮莱吉

Answer 1

问题与调度程序上正在执行的消息的组合无关，而在于您正在调度程序上执行长时间运行的工作。您必须确保在后台线程上执行长时间运行/可能阻塞的操作。最简单的方法是使用BackgroundWorker 组件。

请原谅 C#：

var backgroundWorker = new BackgroundWorker();

backgroundWorker.DoWork += delegate
{
    // long running work goes here
};
backgroundWorker.RunWorkerCompleted += delegate
{
    // change cursor back to normal here
};

// change cursor to busy here

// kick off the background task
backgroundWorker.RunWorkerAsync();