WTF WPF TabControl?

Question

我认为这是WPF（如果有关系，版本为4.0）中的一个bug，但现在已经很晚了，也许我漏掉了什么。

为了举例说明，我绑定到一个虚假的示例：

    <x:Array x:Key="SampleItems" Type="sys:String">
        <sys:String>Foo</sys:String>
        <sys:String>Bar</sys:String>
        <sys:String>Baz</sys:String>
    </x:Array>

这个代码可以正常运行，显示出三个选项卡，它们的标题和内容相同：

<TabControl ItemsSource="{StaticResource SampleItems}">
            <TabControl.ItemContainerStyle>
                <Style TargetType="TabItem">
                    <Setter Property="Header" Value="{Binding}" />
                    <Setter Property="Content" Value="{Binding}" />
                </Style>
            </TabControl.ItemContainerStyle>
        </TabControl>

然而，这会抛出一个异常，错误信息为“Error 10 指定的元素已经是另一个元素的逻辑子元素。请先断开它的连接。”：

<TabControl ItemsSource="{StaticResource SampleItems}">
    <TabControl.ItemContainerStyle>
        <Style TargetType="TabItem">
            <Setter Property="Header">
                <Setter.Value>
                    <!-- Anything here causes this problem. -->
                    <TextBlock Text="{Binding}"/>
                </Setter.Value>
            </Setter>
            <Setter Property="Content" Value="{Binding}" />
        </Style>
    </TabControl.ItemContainerStyle>
</TabControl>

重要的是需要注意，任何TextBlock中的文本都会出现这个问题。实际上，我可以替换标题TextBlock中的任何XAML并获得此消息。我无法解释这个问题。有什么想法，还是这只是一个错误？

在VS设计器中出现了问题，但是在运行时，以下是相关堆栈跟踪的一部分：

   at System.Windows.FrameworkElement.ChangeLogicalParent(DependencyObject newParent)
   at System.Windows.FrameworkElement.AddLogicalChild(Object child)
   at System.Windows.Controls.HeaderedContentControl.OnHeaderChanged(Object oldHeader, Object newHeader)
   at System.Windows.Controls.HeaderedContentControl.OnHeaderChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
   at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
   at System.Windows.StyleHelper.ApplyStyleOrTemplateValue(FrameworkObject fo, DependencyProperty dp)
   at System.Windows.StyleHelper.InvalidateContainerDependents(DependencyObject container, FrugalStructList`1& exclusionContainerDependents, FrugalStructList`1& oldContainerDependents, FrugalStructList`1& newContainerDependents)
   at System.Windows.StyleHelper.DoStyleInvalidations(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle)
   at System.Windows.StyleHelper.UpdateStyleCache(FrameworkElement fe, FrameworkContentElement fce, Style oldStyle, Style newStyle, Style& styleCache)
   at System.Windows.FrameworkElement.OnStyleChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.FrameworkElement.OnPropertyChanged(DependencyPropertyChangedEventArgs e)
   at System.Windows.DependencyObject.NotifyPropertyChange(DependencyPropertyChangedEventArgs args)
   at System.Windows.DependencyObject.UpdateEffectiveValue(EntryIndex entryIndex, DependencyProperty dp, PropertyMetadata metadata, EffectiveValueEntry oldEntry, EffectiveValueEntry& newEntry, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType)
   at System.Windows.DependencyObject.SetValueCommon(DependencyProperty dp, Object value, PropertyMetadata metadata, Boolean coerceWithDeferredReference, Boolean coerceWithCurrentValue, OperationType operationType, Boolean isInternal)
   at System.Windows.DependencyObject.SetValue(DependencyProperty dp, Object value)
   at System.Windows.Controls.ItemsControl.ApplyItemContainerStyle(DependencyObject container, Object item)
   at System.Windows.Controls.ItemsControl.MS.Internal.Controls.IGeneratorHost.PrepareItemContainer(DependencyObject container, Object item)
   at System.Windows.Controls.ItemContainerGenerator.System.Windows.Controls.Primitives.IItemContainerGenerator.PrepareItemContainer(DependencyObject container)
   at System.Windows.Controls.Panel.GenerateChildren()

- Jerry Bullard

Answer 1

基本上，你正在为每个TabItem分配同一个TextBlock实例。在第一次迭代中，TextBlock被添加到第一个TabItem中。在第二次迭代中，完全相同的 TextBlock被添加到视觉树中。你看到的错误消息试图告诉你，TextBlock不能有两个父级（这里有个笑话）。

然而，你可以为它们设置模板。模板指示TabItem为每个创建的项目创建新的任何视觉元素集合。

<TabControl ItemsSource="{StaticResource SampleItems}">
    <TabControl.ItemContainerStyle>
        <Style TargetType="TabItem">
            <Setter Property="HeaderTemplate">
                <Setter.Value>
                    <DataTemplate>
                         <TextBlock Text="{Binding}"/>
                    </DataTemplate>
                </Setter.Value>
            </Setter>
            <Setter Property="Content" Value="{Binding}" />
        </Style>
    </TabControl.ItemContainerStyle>
</TabControl>

- Anderson Imes

---

当然。尽管净XAML大致相同，在工作案例中为每个绑定字符串插入TextBlock，但关键区别在于每个字符串都会生成一个新的TextBlock。在失败的情况下，我告诉它一遍又一遍地使用同一个TextBlock。真是我的错。 - Jerry Bullard