WPF：在DataGridComboBoxColumn中显示验证工具提示

我有一个DataGrid，里面有几个ComboBox列 . 使用ViewModel中的IDataErrorInfo接口验证这些值 . 当鼠标悬停在适当的单元格上时，工具提示应显示验证错误 .

实现此行为的常规方法是使用如下的ElementStyle：

<DataGridComboBoxColumn ...>
  <DataGridComboBoxColumn.ElementStyle>
    <Style TargetType="ComboBox">
      ...
      <Style.Triggers>
        <Trigger Property="Validation.HasError" Value="true">
          <Setter Property="ToolTip"
                  Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}"/>
        </Trigger>
      </Style.Triggers>
    </Style>
  </DataGridComboBoxColumn.ElementStyle>
</DataGridComboBoxColumn>

这适用于DataGridTextColumns但 not 适用于DataGridComboBoxColumns（未显示工具提示） . 如果 Editing ElementStyle使用相同的代码，一切正常 . 但仅当单元格处于编辑模式时（正如预期的那样，因为EditingElementStyle仅用于编辑模式） .

在WWW中找到的这个问题的解决方案是建议使用这样的CellStyle：

<DataGridComboBoxColumn ...>
  <DataGridComboBoxColumn.CellStyle>
    <Style TargetType="DataGridCell">
      <Style.Triggers>
        <DataTrigger Binding="{Binding Path=(Validation.HasError), RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGridRow}}}" 
                     Value="True">
          <Setter Property="ToolTip"
                            Value="{Binding RelativeSource={RelativeSource FindAncestor, AncestorType={x:Type DataGridRow}}, Path=(Validation.Errors)[0].ErrorContent}" />
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </DataGridComboBoxColumn.CellStyle>
</DataGridComboBoxColumn>

此方法使用DataGrid Row 和硬编码索引来获取错误 . 这对我来说似乎非常容易出错 . 无论如何，只要行中只有一个验证错误，它就应该工作 . 但是，只要同一行中存在两个或更多验证错误，它就不再起作用了 . 每个工具提示都显示第一个验证错误（因为硬编码索引）：

因此，我自然而然地使用DataGridCell而不是DataGridRow来获取错误（请参阅下面绑定中的RelativeSource）：

<DataGridComboBoxColumn ...>
  <DataGridComboBoxColumn.CellStyle>
    <Style TargetType="DataGridCell">
      <Style.Triggers>
        <DataTrigger Binding="{Binding Path=(Validation.HasError), RelativeSource={RelativeSource Self}}" 
                     Value="True">
          <Setter Property="ToolTip"
                            Value="{Binding RelativeSource={RelativeSource Self}, Path=(Validation.Errors)[0].ErrorContent}" />
        </DataTrigger>
      </Style.Triggers>
    </Style>
  </DataGridComboBoxColumn.CellStyle>
</DataGridComboBoxColumn>

但是使用此样式，不会显示任何工具提示 . 输出窗口中没有错误或警告 . 将PresentationTraceSources.TraceLevel = High添加到触发器绑定显示，HasError属性返回false .

删除Tooltip绑定周围的触发器时，Validation.Errors似乎不包含任何值：

System.Windows.Data Warning: 56 : Created BindingExpression (hash=13069983) for Binding (hash=50848483)
System.Windows.Data Warning: 58 :   Path: '(0)[0].ErrorContent'
System.Windows.Data Warning: 60 : BindingExpression (hash=13069983): Default mode resolved to OneWay
System.Windows.Data Warning: 61 : BindingExpression (hash=13069983): Default update trigger resolved to PropertyChanged
System.Windows.Data Warning: 62 : BindingExpression (hash=13069983): Attach to System.Windows.Controls.DataGridCell.ToolTip (hash=21168757)
System.Windows.Data Warning: 67 : BindingExpression (hash=13069983): Resolving source 
System.Windows.Data Warning: 70 : BindingExpression (hash=13069983): Found data context element: <null> (OK)
System.Windows.Data Warning: 72 :   RelativeSource.Self found DataGridCell (hash=21168757)
System.Windows.Data Warning: 78 : BindingExpression (hash=13069983): Activate with root item DataGridCell (hash=21168757)
System.Windows.Data Warning: 108 : BindingExpression (hash=13069983):   At level 0 - for DataGridCell.(Validation.Errors) found accessor DependencyProperty(Errors)
System.Windows.Data Warning: 104 : BindingExpression (hash=13069983): Replace item at level 0 with DataGridCell (hash=21168757), using accessor DependencyProperty(Errors)
System.Windows.Data Warning: 101 : BindingExpression (hash=13069983): GetValue at level 0 from DataGridCell (hash=21168757) using DependencyProperty(Errors): ReadOnlyObservableCollection`1 (hash=51278326 Count=0)
System.Windows.Data Warning: 109 : BindingExpression (hash=13069983):   At level 1 - for ReadOnlyObservableCollection`1[] found accessor RuntimePropertyInfo(Item)
System.Windows.Data Warning: 104 : BindingExpression (hash=13069983): Replace item at level 1 with ReadOnlyObservableCollection`1 (hash=51278326 Count=0), using accessor RuntimePropertyInfo(Item)
System.Windows.Data Warning: 101 : BindingExpression (hash=13069983): GetValue at level 1 from ReadOnlyObservableCollection`1 (hash=51278326 Count=0) using RuntimePropertyInfo(Item): {IListIndexOutOfRange}
System.Windows.Data Error: 17 : Cannot get 'Item[]' value (type 'ValidationError') from '(Validation.Errors)' (type 'ReadOnlyObservableCollection`1'). BindingExpression:Path=(0)[0].ErrorContent; DataItem='DataGridCell' (Name=''); target element is 'DataGridCell' (Name=''); target property is 'ToolTip' (type 'Object') ArgumentOutOfRangeException:'System.ArgumentOutOfRangeException: Das angegebene Argument liegt außerhalb des gültigen Wertebereichs.
Parametername: index'
System.Windows.Data Warning: 103 : BindingExpression (hash=13069983): Replace item at level 2 with {NullDataItem}
System.Windows.Data Warning: 80 : BindingExpression (hash=13069983): TransferValue - got raw value {DependencyProperty.UnsetValue}
System.Windows.Data Warning: 88 : BindingExpression (hash=13069983): TransferValue - using fallback/default value <null>
System.Windows.Data Warning: 89 : BindingExpression (hash=13069983): TransferValue - using final value <null>

有人有解决这个问题的方法吗？