为什么在 UWP 的样式设置器中 {x:Null} 不再是有效值? [英] Why is {x:Null} no longer a valid value in a Style Setter in UWP?

问题描述

跟进

我知道将值设置为 {x:Null} 是有效的.如果您直接设置 <ListView Transitions="{x:Null}"/>，那么它可以正常工作......正如预期的那样.

那么……样式设置器发生了什么?...仔细解释一下，微软?至少有替代方法吗?

解决方案

这确实是一种奇怪的行为，总体而言，因为正如您所解释的，直接设置为 null 有效，而使用样式则无效.我发现的唯一选择就是设置一个清晰的 transitioncollection:

<Style x:Key="MyList" TargetType="ListView"><Setter Property="Transitions" ><Setter.Value><TransitionCollection></TransitionCollection></Setter.Value></Setter><Setter Property="DataContext" Value="{x:Null}"/></风格>

我将 DataContext 的示例设置为可以设置为 null，它说同样的错误但编译和工作.

我知道这不是最好的解决方案，但有一个清晰的过渡集合是一种解决方法.

A follow up to this question, why is {x:Null} no longer a valid option for Setter.Value?

Put this code in a resource dictionary in your UWP app:

<Style x:Key="MyList"
        TargetType="ListView">
    <Setter Property="Transitions" 
            Value="{x:Null}"/>
</Style>

And use it in any ListView:

<ListView Style="{StaticResource MyList}"/>

Your app will crash. A nasty crash as well, the kind that takes down the app without breaking properly in your debugger.

Also, the designer complains with a Catastrophic failure:

I know that setting values to {x:Null} is valid. If you set the <ListView Transitions="{x:Null}"/> directly, then it works fine... as expected.

So... what happened with style setters? ... Care to explain, Microsoft? Is there at least an alternate method?

解决方案

It is really a weird behavior and overall because as you explained setting directly to null works and with the style does not. The only alternative I found is just set a clear transitioncollection:

<Page.Resources>
<Style x:Key="MyList" TargetType="ListView">
    <Setter Property="Transitions" >
        <Setter.Value>
            <TransitionCollection></TransitionCollection>
        </Setter.Value>
    </Setter>
    <Setter Property="DataContext" Value="{x:Null}"/>
</Style>

I set the example of the DataContext that can be set to null, it says the same error but compiles and works.

I know it is not the best solution but it is a workaround to have a clear transitioncollection.

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