如何使用 BackgroundWorker 显示/隐藏 WPF UI 元素？

Question

我有一个矩形，我想让它可见，然后我想等待 500 毫秒，然后我想让它再次不可见。

最初我尝试了这段代码：

MuzzleFlash.Visibility = Visibility.Visible;
Thread.Sleep(500);
this.UpdateLayout();
this.InvalidateVisual();
MuzzleFlash.Visibility = Visibility.Collapsed;

我尝试了这两条中间线，因为它们据说会强制更新窗口，但所做的只是暂停半秒钟，而没有更改任何类型的矩形。

所以我听说了 BackgroundWorkers 以及我应该如何使用它们。经过一些简短的阅读，我想出了这个。请注意，Shoot 订阅了 Canvas 上的 MouseDown 事件，该事件以前有效：

private void Shoot(object sender, System.Windows.Input.MouseButtonEventArgs e)
    {

        BackgroundWorker UIUpdater = new BackgroundWorker();
        UIUpdater.WorkerSupportsCancellation = true;
        UIUpdater.WorkerReportsProgress = false;

        UIUpdater.DoWork += new DoWorkEventHandler(UI_DoWork);
        UIUpdater.RunWorkerCompleted += new RunWorkerCompletedEventHandler(cancelUIUpdate);

    }

    private void UI_DoWork(object sender, DoWorkEventArgs e)
    {
        MuzzleFlash.Visibility = Visibility.Visible;
        Thread.Sleep(500);
        this.UpdateLayout();
        this.InvalidateVisual();
        MuzzleFlash.Visibility = Visibility.Collapsed;
    }

    private void cancelUIUpdate(object sender, RunWorkerCompletedEventArgs e)
    {
        BackgroundWorker bw = sender as BackgroundWorker;
        bw.CancelAsync();
    }

现在它甚至没有暂停半秒钟，向我表明工人没有做任何事情。我该如何解决这个问题，并使矩形出现/消失？

Answer 1

在 wpf 中使用后台工作人员管理动画是个坏主意。动画应该从 Storyboard 运行。它可以通过 xaml 或在代码中指定。

使用 xaml 动画矩形的问题非常简单：

<Rectangle x:Name="MuzzleFlash" Height="100" Width="100" Fill="Red">
    <Rectangle.Triggers>
        <EventTrigger RoutedEvent="Loaded">
            <BeginStoryboard>
                <Storyboard>
                    <ObjectAnimationUsingKeyFrames BeginTime="0:0:0.5"  Storyboard.TargetProperty="Visibility">
                        <DiscreteObjectKeyFrame Value="{x:Static Visibility.Collapsed}" />
                    </ObjectAnimationUsingKeyFrames>
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </Rectangle.Triggers>
</Rectangle>

对于更复杂的动画，您可以使用 Blend 进行交互设计。

在 cmets 后更新响应： 如果你想让它出现和消失，你必须从父容器中操作它，因为一旦矩形隐藏，它就不会响应鼠标事件。

您可以将矩形放在网格中并通过名称引用它以更改其在动画中的可见性。

<Grid Background="Gray">
    <Grid.Triggers>
        <EventTrigger RoutedEvent="MouseDown">
            <BeginStoryboard>
                <Storyboard>
                    <ObjectAnimationUsingKeyFrames BeginTime="0:0:0.0"  Storyboard.TargetProperty="Visibility" Storyboard.TargetName="MuzzleFlash">
                        <DiscreteObjectKeyFrame Value="{x:Static Visibility.Visible}" />
                        <DiscreteObjectKeyFrame KeyTime="0:0:0.5" Value="{x:Static Visibility.Hidden}" />
                    </ObjectAnimationUsingKeyFrames>
                </Storyboard>
            </BeginStoryboard>
        </EventTrigger>
    </Grid.Triggers>
    <Rectangle x:Name="MuzzleFlash" Height="100" Width="100" Fill="Red">

    </Rectangle>
</Grid>

Answer 2

如果你使用 MVVm 并且你正在绑定到你的视图模型，那么试试这个

将可见性转换器绑定到矩形并仅在值类似于真假时显示它？

然后在后台工作人员中设置时间前后的值

https://www.rhyous.com/2011/02/22/binding-visibility-to-a-bool-value-in-wpf/

Answer 3

    private BackgroundWorker bw = new BackgroundWorker();

    private void Window_Loaded(object sender, RoutedEventArgs e)
    {
        //Background Worker code///
        bw.WorkerReportsProgress = true;
        bw.DoWork += bw_DoWork;
        bw.ProgressChanged += bw_ProgressChanged;
        bw.RunWorkerCompleted += bw_RunWorkerCompleted;
        bw.RunWorkerAsync();

        //Progress Bar Window
        grdProgress.Visibility = Visibility.Visible;
    }
    private void bw_DoWork(object sender, DoWorkEventArgs e)
    {
        //something to do
    }

    private void bw_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        //Progress Bar Window close
        grdProgress.Visibility = Visibility.Hidden;
    }

    private void bw_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {
        prg.Value = e.ProgressPercentage;
    }


  bw.ReportProgress(value);