当ContentControl的内容为null或为空时显示默认的DataTemplate吗？

问题描述

我认为这是可能的，但显而易见的方法是行不通的。

I would think this is possible, but the obvious way isn't working.

当前，我正在这样做：

<ContentControl
    Content="{Binding HurfView.EditedPart}">
    <ContentControl.Resources>
        <Style
            TargetType="ContentControl"
            x:Key="emptytemplate">
            <Style.Triggers>
                <DataTrigger
                    Binding="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=Content}"
                    Value="{x:Null}">
                    <Setter
                        Property="ContentControl.Template">
                        <Setter.Value>
                            <ControlTemplate>
                                <Grid
                                    HorizontalAlignment="Stretch"
                                    VerticalAlignment="Stretch">
                                    <TextBlock>EMPTY!</TextBlock>
                                </Grid>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ContentControl.Resources>
</ContentControl>

我没有任何绑定错误，因此可以编译。但是，它不会产生预期的结果。我还尝试了显而易见的方法：

I'm not getting any binding errors and this compiles. However, it doesn't produce the expected result. I've also tried the obvious:

<DataTemplate DataType="{x:Null}"><TextBlock>Hurf</TextBlock></DataTemplate>

这不会编译。并且尝试两次设置内容也会失败：

This won't compile. And attempting to set the content twice fails as well:

<ContentControl
    Content="{Binding HurfView.EditedPart}">
        <TextBlock>DEFAULT DISPLAY</TextBlock>
</ContentControl>

是否可以在不编写自定义模板选择器的情况下执行此操作？

Can I do this without writing a custom template selector?

推荐答案

简单，您必须以样式绑定content属性。如果存在绑定，则样式不会覆盖控件上的值，即使该值的值为Null。

Simple, you have to bind the content property in the style. Styles won't overwrite a value on a control if there's a binding present, even if the value evaluates to Null. Try this.

<ContentControl>
    <ContentControl.Style>
        <Style TargetType="ContentControl">
            <Setter Property="Content" Value="{Binding HurfView.EditedPart}" />
            <Style.Triggers>
                <DataTrigger Binding="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=Content}" Value="{x:Null}">
                    <Setter Property="ContentControl.Template">
                        <Setter.Value>
                            <ControlTemplate>
                                <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
                                    <TextBlock>EMPTY!</TextBlock>
                                </Grid>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </ContentControl.Style>
</ContentControl>

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