wpf淡入动画只工作一次

Question

我创建了一个淡入淡出动画，由视图模型中的属性更改触发。这在第一次淡入和淡出时工作正常，但每次我重复此操作时只会显示淡出，这意味着控件在闪烁到不透明度 1 然后淡出之前保持不可见。

XAML：

<DataTemplate x:Key="MessageTemplate">
    <DataTemplate.Triggers>
        <DataTrigger Binding="{Binding FadeInAnimationState}" Value="Active">
            <DataTrigger.EnterActions>
                <BeginStoryboard>
                    <Storyboard>
                        <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="Opacity">
                            <EasingDoubleKeyFrame KeyTime="0" Value="0"/>
                            <EasingDoubleKeyFrame KeyTime="0:0:0.25" Value="1"/>
                        </DoubleAnimationUsingKeyFrames>
                    </Storyboard>
                </BeginStoryboard>
            </DataTrigger.EnterActions>
        </DataTrigger>
        <DataTrigger Binding="{Binding FadeOutAnimationState}" Value="Active">
            <DataTrigger.EnterActions>
                <BeginStoryboard>
                    <Storyboard>
                        <DoubleAnimationUsingKeyFrames Storyboard.TargetProperty="Opacity">
                            <EasingDoubleKeyFrame KeyTime="0" Value="1"/>
                            <EasingDoubleKeyFrame KeyTime="0:0:1" Value="0"/>
                        </DoubleAnimationUsingKeyFrames>
                    </Storyboard>
                </BeginStoryboard>
            </DataTrigger.EnterActions>
        </DataTrigger>
    </DataTemplate.Triggers>
    <StatusBarItem>
        ...
    </StatusBarItem>
</DataTemplate>
...
<ContentPresenter ContentTemplate="{StaticResource MessageTemplate}" Content="{Binding}"/>

负责触发动画的Viewmodel属性：

private DisplayState _messageState;
private DisplayState MessageState
{
    get { return _messageState; }
    set
    {
        _messageState = value;
        if (value == DisplayState.Displayed)
        {
            FadeOutAnimationState = AnimationState.Inactive;
            FadeInAnimationState = AnimationState.Active;
        }
        else
        {
            FadeInAnimationState = AnimationState.Inactive;
            FadeOutAnimationState = AnimationState.Active;
        }
    }
}

public AnimationState FadeInAnimationState
{
    ... // getter and setter with NotfiyPropertyChanged
}

public AnimationState FadeOutAnimationState
{
    ... // getter and setter with NotfiyPropertyChanged
}

以及调用（调试）：

MessageState = DisplayState.Displayed;
await Task.Delay(duration);
MessageState = DisplayState.Hidden;
await Task.Delay(TimeSpan.FromSeconds(1));

我在做什么啊？

Answer 1

完成后，您需要删除情节提要。比如：

 <DataTrigger.EnterActions>
   <RemoveStoryboard BeginStoryboardName="FadeIn" />
   <RemoveStoryboard BeginStoryboardName="FadeOut" />       
   <BeginStoryboard Name="FadeIn">           
       <Storyboard>
          ...
       </Storyboard>
   </BeginStoryboard>
 </DataTrigger.EnterActions>

（FadeOut 也一样，给它一个名字）

或者，您可以在ExitActions：

 <DataTrigger.EnterActions>
   <BeginStoryboard Name="FadeIn">           
       <Storyboard>
          ...
       </Storyboard>
   </BeginStoryboard>
 </DataTrigger.EnterActions>
 <DataTrigger.ExitActions>
   <RemoveStoryboard BeginStoryboardName="FadeIn" />
 </DataTrigger.ExitActions>

否则最后一个故事板将继续“推送”其最后一个值，因此您将看不到任何更改