WPF：如何调试绑定错误？

I'm getting this in my output Window:

我在输出窗口中得到了这个：

System.Windows.Data Error: 4 : Cannot find source for binding with reference 'RelativeSource FindAncestor, AncestorType='System.Windows.Controls.ItemsControl', AncestorLevel='1''. BindingExpression:Path=VerticalContentAlignment; DataItem=null; target element is 'ListBoxItem' (Name=''); target property is 'VerticalContentAlignment' (type 'VerticalAlignment')

System.Windows.Data错误：4：无法找到与引用'RelativeSource FindAncestor绑定的源，AncestorType ='System.Windows.Controls.ItemsControl'，AncestorLevel ='1''。 BindingExpression：路径= VerticalContentAlignment;的DataItem = NULL; target元素是'ListBoxItem'（Name =''）; target属性是'VerticalContentAlignment'（类型'VerticalAlignment'）

This is my XAML, which when run looks correct

这是我的XAML，运行时看起来是正确的

        <GroupBox Header="Grant/Deny Report">
            <ListBox ItemsSource="{Binding  Converter={StaticResource MethodBinder}, ConverterParameter=GrantDeny, Mode=OneWay}">
                <ListBox.ItemTemplate>
                    <DataTemplate>
                        <StackPanel Orientation="Horizontal">
                            <Label Content="{Binding Entity}"/>
                            <Label Content="{Binding HasPermission}"/>
                        </StackPanel>
                    </DataTemplate>
                </ListBox.ItemTemplate>
            </ListBox>
        </GroupBox>

2 个解决方案

#1

I was also going to recommend Bea Stollnitz's article but Jonathan Allen got his post in while I was still typing this one. I also recommend the links in this blog entry.

我还打算推荐Bea Stollnitz的文章，但Jonathan Allen在我还在输入这篇文章的时候得到了他的职位。我还推荐此博客条目中的链接。

In this particular case you can see that somewhere a ListBoxItem has a FindAncestor binding to an ItemsControl that is failing. That tells you right away there is a ListBoxItem somewhere that is either:

在这种特殊情况下，您可以看到ListBoxItem的某个地方有FindAncestor绑定到失败的ItemsControl。这告诉你马上有一个ListBoxItem，它是：

Not in the visual tree, or
不在视觉树中，或
Not under an ItemsControl (a ListBox is an ItemsControl)
不在ItemsControl下（ListBox是ItemsControl）

In addition, you know that someone, somewhere, is binding a ListBoxItem's VerticalContentAlignment property to FindAncestor.

此外，您知道有人在某处将ListBoxItem的VerticalContentAlignment属性绑定到FindAncestor。

Looking at the system themes (shipped with Expression Blend and also available through NET Reflector's BAMLViewer Add-in), we see this:

查看系统主题（Expression Blend附带，也可以通过NET Reflector的BAMLViewer外接程序获得），我们看到：

<Style x:Key="{x:Type ListBoxItem}">
  <Setter Property="VerticalContentAlignment"
          Value="{Binding Path=VerticalContentAlignment,RelativeSource={RelativeSource AncestorType={x:Type ItemsControl}}" />

This explains where the binding comes from. The next question is, how is a ListBoxItem being created that is not under a ListBox (or other ItemsControl)?

这解释了绑定的来源。接下来的问题是，如何创建一个不在ListBox（或其他ItemsControl）下的ListBoxItem？

Some things to look for:

有些事要寻找：

Are you constructing ListBoxItems in code anywhere?
你在任何地方的代码中构建ListBoxItems？
Is there any ListBoxItem explicitly specified in your XAML?
是否在您的XAML中明确指定了任何ListBoxItem？
Do you have any code that manually manipulates the items in ListBox?
你有任何手动操作ListBox中的项目的代码吗？

Hopefully this will head you in the right direction.

希望这会引导您朝着正确的方向前进。

#2

I ran into a similar problem with the TreeView (though my data binding errors showed up as being Informational).

我遇到了与TreeView类似的问题（虽然我的数据绑定错误显示为信息）。

I solved the problem by defining an implicit style in the TreeView resource for TreeViewItem. Within that style I defined the missing vertical and horizontal content alignment properties.

我通过在TreeViewItem的TreeView资源中定义隐式样式来解决问题。在该样式中，我定义了缺少的垂直和水平内容对齐属性。

<TreeView.Resources>
     <Style TargetType="{x:Type TreeViewItem}" >
          <Setter Property="VerticalContentAlignment" Value="Stretch"/>
          <Setter Property="HorizontalContentAlignment" Value="Stretch"/>
     </Style>
</TreeView.Resources>

#1