为什么WPF中的TextBox.Text无法设置动画？ [英] Why isn't TextBox.Text in WPF animatable?

问题描述

好吧，我遇到了一些真正让我措手不及的事情。

Ok, I have just run into something that is really catching me off-guard.

我正在帮助同一个开发人员解决几个不相关的问题，他正在将文本动画化为一些TextBlock（s）。因此，我回到办公桌并重新创建了该项目（以回答他的问题），但是我不小心使用了 TextBox 而不是 TextBlock 。我的文字根本没有动画！ （有很多帮助！）

I was helping a fellow developer with a couple of unrelated questions and in his project he was animating text into some TextBlock(s). So, I went back to my desk and recreated the project (in order to answer his questions), but I accidentally used TextBox instead of TextBlock. My text wasn't animating at all! (A lot of help, I was!)

最终，我发现他的xaml使用的是TextBlock，而我的使用的是TextBox。有趣的是，当我使用TextBox时Blend并没有创建关键帧。因此，我使用TextBlock使它在Blend中工作，然后手动修改了xaml，将TextBlock转换为TextBox。当我运行该项目时，出现以下错误：

Eventually, I figured out that his xaml was using TextBlock and mine was using TextBox. What is interesting, is that Blend wasn't creating key frames when I was using TextBox. So, I got it to work in Blend using TextBlock(s) and then modified the xaml by hand, converting the TextBlock(s) into TextBox(es). When I ran the project, I got the following error:

InvalidOperationException：'（0）'Storyboard.TargetProperty路径包含不可动画的属性'Text' 。

好吧，Blend似乎足够聪明，可以知道...而不会在动画中生成关键帧（它将直接在TextBox上修改值）。 +1为Blend。

Well, it seems as if Blend was smart enough to know that ... and not generate the key frames in the animation (it would just modify the value directly on the TextBox). +1 for Blend.

因此，问题变成了：为什么TextBox.Text无法动画化？通常的答案是您要设置动画的特定属性不是DependencyProperty。但是，情况并非如此，TextBox.Text 是一个DependencyProperty。

So, the question became: why isn't TextBox.Text animatable? The usual answer is that the particular property you are animating isn't a DependencyProperty. But, this isn't the case, TextBox.Text is a DependencyProperty.

所以，现在我很困惑！ 为什么不能设置TextBox.Text的动画？

So, now I am bewildered! Why can't you animate TextBox.Text?

让我加入一些xaml来说明问题。以下xaml可以工作...但是使用的是TextBlock。

Let me include some xaml to illustrate the problem. The following xaml works ... but uses TextBlock(s).

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="TextBoxTextQuestion.MainWindow"
    x:Name="Window"
    Title="MainWindow"
    Width="640"
    Height="480"
>
    <Window.Resources>
        <Storyboard x:Key="animateTextStoryboard">
            <StringAnimationUsingKeyFrames Storyboard.TargetProperty="(TextBlock.Text)" Storyboard.TargetName="textControl">
                <DiscreteStringKeyFrame KeyTime="0:0:1" Value="Goodbye"/>
            </StringAnimationUsingKeyFrames>
        </Storyboard>
    </Window.Resources>
    <Window.Triggers>
        <EventTrigger RoutedEvent="FrameworkElement.Loaded">
            <BeginStoryboard Storyboard="{StaticResource animateTextStoryboard}"/>
        </EventTrigger>
    </Window.Triggers>
    <Grid x:Name="LayoutRoot">
        <StackPanel Orientation="Vertical" HorizontalAlignment="Center" VerticalAlignment="Center">
            <TextBlock x:Name="textControl" Text="Hello" FontFamily="Calibri" FontSize="32"/>
            <TextBlock Text="World!" Margin="0,25,0,0" FontFamily="Calibri" FontSize="32"/>
        </StackPanel>
    </Grid>
</Window>

以下xaml 不起作用，并使用TextBox.Text：

The following xaml does not work and uses TextBox.Text:

<Window
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="TextBoxTextQuestion.MainWindow"
    x:Name="Window"
    Title="MainWindow"
    Width="640"
    Height="480"
>
    <Window.Resources>
        <Storyboard x:Key="animateTextStoryboard">
            <StringAnimationUsingKeyFrames Storyboard.TargetProperty="(TextBox.Text)" Storyboard.TargetName="textControl">
                <DiscreteStringKeyFrame KeyTime="0:0:1" Value="Goodbye"/>
            </StringAnimationUsingKeyFrames>
        </Storyboard>
    </Window.Resources>
    <Window.Triggers>
        <EventTrigger RoutedEvent="FrameworkElement.Loaded">
            <BeginStoryboard Storyboard="{StaticResource animateTextStoryboard}"/>
        </EventTrigger>
    </Window.Triggers>
    <Grid x:Name="LayoutRoot">
        <StackPanel Orientation="Vertical" HorizontalAlignment="Center" VerticalAlignment="Center">
            <TextBox x:Name="textControl" Text="Hello" FontFamily="Calibri" FontSize="32"/>
            <TextBox Text="World!" Margin="0,25,0,0" FontFamily="Calibri" FontSize="32"/>
        </StackPanel>
    </Grid>
</Window>

推荐答案

尝试手动为TextBox设置动画效果。 / p>

Trying to animate the TextBox manually ....

var timeline = new StringAnimationUsingKeyFrames();
timeline.KeyFrames.Add(new DiscreteStringKeyFrame("Goodbye", KeyTime.FromTimeSpan(new TimeSpan(0,0,1))));
textControl.BeginAnimation(TextBox.TextProperty, timeline);

...显示了一个更有用的错误消息。最后一行失败，并显示以下 ArgumentException ：

...reveals a more useful error message. The last line fails with the following ArgumentException:

'Text'属性不是可以在'System.Windows.Controls.TextBox'类上进行动画处理，因为已在用于将该属性与该类相关联的UIPropertyMetadata上设置了IsAnimationProhibited标志。

参数名称：dp

'Text' property is not animatable on 'System.Windows.Controls.TextBox' class because the IsAnimationProhibited flag has been set on the UIPropertyMetadata used to associate the property with the class.
Parameter name: dp

UIPropertyMetadata.IsAnimationProhibited 说：

通常，Windows Presentation Foundation中可用的默认依赖项属性（WPF）框架实现API可以动画化。您可以在自己的自定义依赖项属性的元数据中将此属性设置为true，以禁用其上的动画。

In general, the default dependency properties available in the Windows Presentation Foundation (WPF) framework implementation APIs can be animated. You might set this property to true in the metadata of your own custom dependency property to disable animations on it.

显然， WPF库认为对TextBox的 Text 依赖属性进行动画处理不是一个好主意，并明确禁用了它。

Apparently, the designers of the WPF library decided that animating the Text depdendency property of a TextBox is not a good idea and explicitly disabled it.

因此，这是为什么无法对此属性设置动画的技术答案。他们为什么禁用它？我不知道...

So, that's the technical answer as to why this property cannot be animated. Why did they disable it? I have no idea...

PS：快速查看 TextBox ， TextBoxBase 和带有反射器的 Control 显示 Text 是唯一的TextBox依赖项属性不能动画。

PS: A quick look at the static constructors of TextBox, TextBoxBase and Control with Reflector reveals that Text is the only TextBox dependency property that cannot be animated.

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