WPF中的Application.DoEvents()在哪里？

Question

我有以下示例代码,每次按下按钮时缩放:

XAML:

<Window x:Class="WpfApplication12.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525">

    <Canvas x:Name="myCanvas">

        <Canvas.LayoutTransform>
            <ScaleTransform x:Name="myScaleTransform" />
        </Canvas.LayoutTransform> 

        <Button Content="Button" 
                Name="myButton" 
                Canvas.Left="50" 
                Canvas.Top="50" 
                Click="myButton_Click" />
    </Canvas>
</Window>

*的.cs

public partial class MainWindow : Window
{
    public MainWindow()
    {
        InitializeComponent();
    }

    private void myButton_Click(object sender, RoutedEventArgs e)
    {
        Console.WriteLine("scale {0}, location: {1}", 
            myScaleTransform.ScaleX,
            myCanvas.PointToScreen(GetMyByttonLocation()));

        myScaleTransform.ScaleX =
            myScaleTransform.ScaleY =
            myScaleTransform.ScaleX + 1;

        Console.WriteLine("scale {0}, location: {1}",
            myScaleTransform.ScaleX,
            myCanvas.PointToScreen(GetMyByttonLocation()));
    }

    private Point GetMyByttonLocation()
    {
        return new Point(
            Canvas.GetLeft(myButton),
            Canvas.GetTop(myButton));
    }
}

输出是:

scale 1, location: 296;315
scale 2, location: 296;315

scale 2, location: 346;365
scale 3, location: 346;365

scale 3, location: 396;415
scale 4, location: 396;415

正如你所看到的那样,有一个问题,我认为通过使用Application.DoEvents();但是......它在.NET 4 中不存在先验.

该怎么办？

Answer 1

尝试这样的事情

public static void DoEvents()
{
    Application.Current.Dispatcher.Invoke(DispatcherPriority.Background,
                                          new Action(delegate { }));
}

Answer 2

好吧,我刚刚开始研究一个在Dispatcher线程上运行的方法,并且需要在不阻塞UI线程的情况下阻塞.事实证明,msdn解释了如何基于Dispatcher本身实现DoEvents():

public void DoEvents()
{
    DispatcherFrame frame = new DispatcherFrame();
    Dispatcher.CurrentDispatcher.BeginInvoke(DispatcherPriority.Background,
        new DispatcherOperationCallback(ExitFrame), frame);
    Dispatcher.PushFrame(frame);
}

public object ExitFrame(object f)
{
    ((DispatcherFrame)f).Continue = false;

    return null;
}

(取自Dispatcher.PushFrame方法)

Answer 3

在WPF中不推荐使用旧的Application.DoEvents()方法,而是使用Dispatcher或后台工作线程来执行您所描述的处理.有关如何使用这两个对象的文章,请参阅链接.

如果您绝对必须使用Application.DoEvents(),那么您只需将system.windows.forms.dll导入您的应用程序并调用该方法即可.但是,这不建议使用,因为您正在失去WPF提供的所有优势.

Answer 4

如果您只需要更新窗口图形，最好像这样使用

public static void DoEvents()
{
    Application.Current.Dispatcher.Invoke(DispatcherPriority.Render,
                                          new Action(delegate { }));
}

Answer 5

myCanvas.UpdateLayout();

似乎也运作良好.