wpf - 当文本在 TextBlock 内换行时，ActualHeight 不正确

Question

我有一个 TextBlock，周围有一个 Border，它位于 Canvas 内部，我用它来将其动画化，作为自定义控件。该 block 从屏幕底部滑入图像顶部。我试图使用 TextBlock 的 ActualHeight 来确定将其移动到页面上的距离，但是当文本太多时，它会换行为两行， ActualHeight 返回与单行相同的大小。

文本 block :

<DataTemplate DataType="{x:Type contentTypes:BusinessAdText}" x:Key="BusinessAdTextTemplate">
    <Border Background="#a9a9a975"
        Width="{Binding RelativeSource={RelativeSource AncestorType={x:Type Canvas}}, Path=ActualWidth}">
        <TextBlock Margin="20" Text="{Binding Text}"
            TextWrapping="Wrap">
        </TextBlock>
        </Border>
</DataTemplate>

应用此样式时具有 Canvas :

<Style TargetType="local:BusinessAd">
    <Setter Property="Template">
        <Setter.Value>
            <ControlTemplate TargetType="local:BusinessAd">
                <Border Background="Transparent">

                    <Canvas ClipToBounds="True">
                        <ContentPresenter x:Name="PART_Content"                                                  
                                            VerticalAlignment="Center"
                                            HorizontalAlignment="Center" />
                    </Canvas>

                </Border>
            </ControlTemplate>
        </Setter.Value>
    </Setter>
</Style>

BusinessAd.cs 的代码隐藏有:

public override void OnApplyTemplate()
{
    base.OnApplyTemplate();
    _contentPart = GetTemplateChild("PART_Content") as FrameworkElement;                        
}

然后只需使用一个简单的 DoubleAnimation 将其移动到屏幕上:

if (_contentPart != null && _isLoaded)
{
    _storyboard.Stop();

    vAnimation.From = ActualHeight;
    vAnimation.To = ActualHeight - _contentPart.ActualHeight;
    //_contentPart.ActualHeight returns 46.something no matter how much text is there

    vAnimation.Duration = new Duration(TimeSpan.FromSeconds(Duration));

    if (_storyboard.Children.Count == 0)
    {
        _storyboard.Children.Add(vAnimation);

        Storyboard.SetTargetProperty(vAnimation, new PropertyPath("(Canvas.Top)"));
        Storyboard.SetTarget(vAnimation, _contentPart);                                                           
    }

    _storyboard.Begin();
}

Answer 1

在检查 ActualHeight 之前，您必须调用 UpdateLayout():

if (_contentPart != null && _isLoaded)
{
    _storyboard.Stop();
    UpdateLayout();

    vAnimation.From = ActualHeight;
    vAnimation.To = ActualHeight - _contentPart.ActualHeight;
    //_contentPart.ActualHeight returns 46.something no matter how much text is there

    vAnimation.Duration = new Duration(TimeSpan.FromSeconds(Duration));

    if (_storyboard.Children.Count == 0)
    {
        _storyboard.Children.Add(vAnimation);

        Storyboard.SetTargetProperty(vAnimation, new PropertyPath("(Canvas.Top)"));
        Storyboard.SetTarget(vAnimation, _contentPart);                                                           
    }

    _storyboard.Begin();
}