WPF 文本块 TargetNullValue 不起作用?

问题描述

我有一个 wpf 文本块，如下所示:

I have a wpf textblock as below:

<TextBlock Text="{Binding [someViewModel].SomeVar.SomeSubVar.Name,
                          TargetNullValue='-'}"/>

在我的视图模型方面，我将有自己的逻辑，最终 SomeVar.SomeSubVar 将为空.

At my viewmodel side, I'll have my own logic that in the end, SomeVar.SomeSubVar will be null.

如果我想显示此 TextBlock 的默认值，我知道我可以声明并启动 SomeVar.SomeSubVar 并将默认值分配给 SomeVar.SomeSubVar.Name 但我想改用 TargetNullValue .我可以知道哪个部分有问题吗?

If I want to show a default value for this TextBlock I know I can declare and initiate SomeVar.SomeSubVar and assign default value into SomeVar.SomeSubVar.Name but I would like to use TargetNullValue instead. May I know which part is wrong?

推荐答案

您可能会考虑使用 FallbackValue http://msdn.microsoft.com/en-us/library/system.windows.data.bindingbase.fallbackvalue(v=vs.110)).aspx 与 TargetNullValue 结合使用.

You might look at using FallbackValue http://msdn.microsoft.com/en-us/library/system.windows.data.bindingbase.fallbackvalue(v=vs.110).aspx in conjunction with TargetNullValue.

为了使 TargetNullValue 起作用，您必须能够将 [someViewModel].SomeVar.SomeSubVar.Name 的完整路径评估为 null.如果someViewModel"、SomeVar"或SomeSubVar"为空，则永远无法评估Name"，并且 TargetNullValue 将不适用.

In order for TargetNullValue to work you must be able to evaluate the full path of [someViewModel].SomeVar.SomeSubVar.Name to null. If 'someViewModel', 'SomeVar', or 'SomeSubVar' are null then 'Name' can never be evaluated, and TargetNullValue won't apply.

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