对象的ActualHeight和ActualWidth始终为零

Question

我有Canvas一个TextBlock像这样:

<Canvas x:Name="ContentPanel" Grid.Row="1" DoubleTapped="ContentPanel_DoubleTapped">
        <TextBlock x:Name="WordBlock" FontSize="226.667" FontFamily="Segoe UI Semilight" TextAlignment="Center"
                   RenderTransformOrigin="0.5, 0.5">
            <TextBlock.RenderTransform>
                <TranslateTransform x:Name="translate"/>
            </TextBlock.RenderTransform>
        </TextBlock>
    </Canvas>

我的应用程序是这样的,当用户导航到此页面时,TextBlock将以中心为中心Canvas,如果TextBlock宽度大于画布的宽度,则会出现选框动画:

private void SetAnimation()
{
    Canvas.SetLeft(WordBlock, (ContentPanel.ActualWidth - WordBlock.ActualWidth) / 2);
    Canvas.SetTop(WordBlock, (ContentPanel.ActualHeight - WordBlock.ActualHeight) / 2);

    if (WordBlock.ActualWidth > ContentPanel.ActualWidth)
    {
        MarqueeAnimation.From = WordBlock.ActualWidth;
        MarqueeAnimation.To = -WordBlock.ActualWidth;
        MarqueeAnimation.Duration = new Duration(new TimeSpan(0, 0, 10));
        MarqueeBoard.Begin();
    }
}

此方法称为OnNavigatedTo.我无法弄清楚为什么TextBlock不会居中,因为ActualHeight和ActualWidth属性总是以0.0的形式返回.我不想放置固定大小,因为这是一个Windows应用商店应用程序,并希望它可以在不同的屏幕尺寸上进行扩展.

有任何想法吗？我被卡住了.

Answer 1

当OnNavigatedTo被调用时,我不相信页面实际上已被绘制.在尝试调整大小和重新排列时,我有类似的困惑.答案似乎是等到页面加载后再进行计算:

public ChallengePage()
{
  this.InitializeComponent();
  this.Loaded += ChallengePage_Loaded;
}

void ChallengePage_Loaded(object sender, RoutedEventArgs e)
{
  *Do your calculations which use ActualWidth and ActualHeight in here*
}

你需要我相信的东西.将Loaded处理程序添加到页面的初始化中,然后可以从那里调用SetAnimation.