WPF：防止“已完成”事件在删除动画后触发

Question

如何从WPF元素中删除正在运行的动画，以使其Completed事件不会触发？

提供的解决方案为here和here删除动画的可见效果，但Completed事件在动画完成时仍会触发。

下面是一些代码，演示了我的问题（这是在一个标签，一个按钮的窗口背后的代码，和一个TextBox）：

int _count = 0; 

    private void button1_Click(object sender, RoutedEventArgs e) { 
     myLabel.Content = "Starting animation: " + _count++; 

     // Cancel any already-running animations and return 
     // the label opacity to 1.0. 
     myLabel.BeginAnimation(Label.OpacityProperty, null); 
     myLabel.Opacity = 1.0; 

     // Create a new animation to fade out the label. 
     DoubleAnimation opacityAnim = new DoubleAnimation(1.0, 0.0, TimeSpan.FromSeconds(2), FillBehavior.Stop) { 
      BeginTime = TimeSpan.FromSeconds(3) 
     }; 
     opacityAnim.Completed += (sndr, ev) => { 
      myTextbox.Text += Environment.NewLine + "Completed fired."; 
     }; 

     // Start the countdown/animation. 
     myLabel.BeginAnimation(Label.OpacityProperty, opacityAnim); 
    } 

如何删除的动画，使得它不会提高其Completed事件？

Answer 1

从已完成的情况下取消...这也意味着你必须从lambda来显式方法重写完成事件处理程序：

DoubleAnimation _opacityAnim; // Created somewhere else. 

    private void button1_Click(object sender, RoutedEventArgs e) 
    { 
    myLabel.Content = "Starting animation: " + _count++; 

    // Cancel any already-running animations and return 
    // the label opacity to 1.0. 
    _opacityAnim.Completed -= AnimationCompleted; 

    myLabel.BeginAnimation(Label.OpacityProperty, null); 
    myLabel.Opacity = 1.0; 

    // Create a new animation to fade out the label. 
    opacityAnim.Completed += AnimationCompleted; 

    // Start the countdown/animation. 
    myLabel.BeginAnimation(Label.OpacityProperty, opacityAnim); 
} 

private void AnimationCompleted(object sender, EventArgs e) 
{ 
     myTextbox.Text += Environment.NewLine + "Completed fired."; 
}