WPF ComboBox SelectedItem在TabControl开关上设置为Null [英] WPF ComboBox SelectedItem Set to Null on TabControl Switch

问题描述

我的WPF应用程序中有一个简单的问题，使我无法自拔.我有一个TabControl，其中每个TabItem都是使用类似于以下内容的DataTemplate为ViewModel生成的View:

I've got a simple problem in my WPF application which has me banging my head on the table. I have a TabControl, where every TabItem is a View generated for a ViewModel using a DataTemplate similar to this:

<DataTemplate DataType="{x:Type vm:FooViewModel}">
    <vw:FooView/>
</DataTemplate>

FooView包含一个ComboBox:

FooView contains a ComboBox:

<ComboBox ItemsSource="{Binding Path=BarList}" DisplayMemberPath="Name" SelectedItem="{Binding Path=SelectedBar}"/>

和FooViewModel包含一个简单的属性:public Bar SelectedBar { get; set; }.我的问题是，当我为ComboBox设置值时，切换到另一个选项卡，然后再改回来，ComboBox再次为空.如果我在属性的设置器上设置断点，则当我切换到另一个选项卡时，会看到该属性已分配给null.

and FooViewModel contains a simple Property: public Bar SelectedBar { get; set; }. My problem is that when I set the value for my ComboBox, change to another tab, then change back, the ComboBox is empty again. If I set a breakpoint on the setter for my property, I see that the property is assigned to null when I switch to another tab.

据我了解，切换选项卡时，会将其从VisualTree中删除-但是为什么将ViewModel的属性设置为null?这使我很难保持持久状态，并且检查value != null似乎不是正确的解决方案.任何人都可以在这种情况下摆脱困境吗?

From what I understand, when a tab is switched, it is removed from the VisualTree - but why is it setting my ViewModel's property to null? This is making it very difficult for me to hold persistent state, and checking value != null does not seem like the right solution. Can anyone shed some like on this situation?

在设置器断点处的调用堆栈仅显示[外部代码]-那里没有提示.

The call stack at the setter breakpoint only shows [External Code] - no hints there.

推荐答案

我们只是遇到了同样的问题.我们找到了描述问题的博客条目.看来这是WPF中的错误，并且有一种解决方法: 在ItemsSource绑定之前指定之前的SelectedItem绑定，问题应该消失了.

we just ran into the same problem. We found a blog entry describing the problem. It looks like it is a bug in WPF and there is a workaround: Specify the SelectedItem binding before the ItemsSource binding and the problem should be gone.

博客文章的链接:

http://www.metanous.be/pharcyde/post/Bug-in-WPF-combobox-databinding.aspx

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