绑定到 DataContext 的 WPF 样式 DataTrigger 不起作用 [英] WPF Style DataTrigger with binding to DataContext not working

问题描述

我有一个带有样式的 TextBox，它有一个 DataTrigger 可以更改文本，如下所示:

I have a TextBox with a style that has a DataTrigger which changes the text, like this:

<Grid>
    <TextBlock Text="Foo">
        <TextBlock.Style>
            <Style BasedOn="{StaticResource TextStyle}" TargetType="TextBlock">
                <Style.Triggers>
                    <DataTrigger Binding="{Binding MyBool}" Value="True">
                        <Setter Property="Text" Value="Bar"/>
                    </DataTrigger>
                 </Style.Triggers>
             </Style>
         </TextBlock.Style>
     </TextBlock>
</Grid>

但它不起作用，文本永远不会更改为Bar".我已经使用另一个带有 Text="{Binding MyBool}" 的 TextBlock 进行了测试，并且此文本从False"变为True".Snoop 没有发现我能看到的任何错误，输出中也没有任何内容.

But it's not working, the text never changes to "Bar". I have tested using another TextBlock with Text="{Binding MyBool}" and this text changes from "False" to "True". Snoop reveals no errors that I can see and there is nothing in the output.

这个问题可能看起来像 WPF 触发器绑定到 MVVM 属性，但我的代码似乎与那里接受的答案没有什么不同(http://www.thejoyofcode.com/Help_Why_cant_I_use_DataTriggers_with_controls_in_WPF.aspx，使用样式"部分)以任何相关方式.并且按照实际答案中的建议使用 DataTemplate 似乎是错误的，因为我只想将其应用于单个 TextBlock，但如果它是正确的，我不确定如何为此编写 DataTemplate...

This question may seem like a duplicate of WPF Trigger binding to MVVM property, but my code does not seem different from the accepted answer there (http://www.thejoyofcode.com/Help_Why_cant_I_use_DataTriggers_with_controls_in_WPF.aspx, section "Using a style") in any relevant way. And using a DataTemplate as suggested in the actual answer seems wrong since I only want this to apply to a single TextBlock, but if it is correct, I'm not sure how to write a DataTemplate for this...

这是我要绑定的属性的样子:

This is what the property I'm binding to looks like:

public bool MyBool
{
    get { return _myBool; }
    set
    {
        if (_myBool== value)
            return;

        _myBool= value;
        NotifyPropertyChanged();
    }
}
private bool _myBool;

推荐答案

Dependency Properties 可以从很多不同的地方设置；内联、动画、强制、触发器等.因此 Dependency Property Value Precedence 列表已创建，这决定了哪些更改会覆盖哪些其他更改.由于这种优先顺序，我们不能使用 Trigger 来更新在 XAML 中显式设置的内联属性.试试这个:

Dependency Properties can be set from many different places; inline, animations, coercion, triggers, etc. As such a Dependency Property Value Precedence list was created and this dictates which changes override which other changes. Because of this order of precedence, we can't use a Trigger to update a property that is explicitly set inline in your XAML. Try this instead:

<Grid>
    <TextBlock>
        <TextBlock.Style>
            <Style BasedOn="{StaticResource TextStyle}" TargetType="TextBlock">
                <!-- define your default value here -->
                <Setter Property="Text" Value="Foo" />
                <Style.Triggers>
                    <DataTrigger Binding="{Binding MyBool}" Value="True">
                        <!-- define your triggered value here -->
                        <Setter Property="Text" Value="Bar" />
                    </DataTrigger>
                 </Style.Triggers>
             </Style>
         </TextBlock.Style>
     </TextBlock>
</Grid>

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