WPF 错误: 找不到控制目标元素的 FrameworkElement

我得到了一个带有图像的行的 DataGrid。该图像与触发器绑定到某种状态。当状态改变时，我想改变图像。

模板本身设置在 DataGridTemplateColumn的 HeaderStyle上。这个模板有一些绑定。第一个绑定日显示它是哪一天，国家用触发器改变图像。

这些属性在 ViewModel 中设置。

物业:

public class HeaderItem
{
public string Day { get; set; }
public ValidationStatus State { get; set; }
}


this.HeaderItems = new ObservableCollection<HeaderItem>();
for (int i = 1; i < 15; i++)
{
this.HeaderItems.Add(new HeaderItem()
{
Day = i.ToString(),
State = ValidationStatus.Nieuw,
});
}

达塔格里德:

<DataGrid x:Name="PersoneelsPrestatiesDataGrid" HorizontalAlignment="Stretch" VerticalAlignment="Stretch"
AutoGenerateColumns="False" SelectionMode="Single" ItemsSource="{Binding CaregiverPerformances}" FrozenColumnCount="1" >


<DataGridTemplateColumn HeaderStyle="{StaticResource headerCenterAlignment}" Header="{Binding HeaderItems[1]}" Width="50">
<DataGridTemplateColumn.CellEditingTemplate>
<DataTemplate>
<TextBox Text="{ Binding Performances[1].Duration,Converter={StaticResource timeSpanConverter},Mode=TwoWay}"/>
</DataTemplate>
</DataGridTemplateColumn.CellEditingTemplate>


<DataGridTemplateColumn.CellTemplate>
<DataTemplate>
<TextBlock TextAlignment="Center" Text="{ Binding Performances[1].Duration,Converter={StaticResource timeSpanConverter}}"/>
</DataTemplate>
</DataGridTemplateColumn.CellTemplate>
</DataGridTemplateColumn>
</DataGrid>

Datagrid Header 样式模板:

<Style x:Key="headerCenterAlignment" TargetType="{x:Type DataGridColumnHeader}">
<Setter Property="HorizontalContentAlignment" Value="Center"/>


<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type DataGridColumnHeader}">
<Grid>
<Grid.RowDefinitions>
<RowDefinition />
<RowDefinition />
</Grid.RowDefinitions>


<TextBlock Grid.Row="0" Text="{Binding Day}" />
<Image x:Name="imageValidation" Grid.Row="1" Width="16" Height="16" Source="{StaticResource imgBevestigd}" />
</Grid>


<ControlTemplate.Triggers>
<MultiDataTrigger >
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding State}" Value="Nieuw"/>
</MultiDataTrigger.Conditions>
<Setter TargetName="imageValidation" Property="Source" Value="{StaticResource imgGeenStatus}"/>
</MultiDataTrigger>
</ControlTemplate.Triggers>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

现在，当我启动这个项目时，图片没有显示，我得到了这个错误:

系统。窗户。数据错误: 2: 找不到控制目标元素的 FrameworkElement 或 FrameworkContentElement。BindingExpression: Path = HeaderItems [0] ; Dataltem = null; target 元素是“ DataGridTemplateColumn”(HashCode = 26950454) ; target 属性是“ Header”(类型为“ Object”)

为什么会显示这个错误？

63576 次浏览
小开
最佳答案

Sadly any DataGridColumn hosted under DataGrid.Columns is not part of Visual tree and therefore not connected to the data context of the datagrid. So bindings do not work with their properties such as Visibility or Header etc (although these properties are valid dependency properties!).

Now you may wonder how is that possible? Isn't their Binding property supposed to be bound to the data context? Well it simply is a hack. The binding does not really work. It is actually the datagrid cells that copy / clone this binding object and use it for displaying their own contents!

So now back to solving your issue, I assume that HeaderItems is a property of the object that is set as the DataContext of your parent View. We can connect the DataContext of the view to any DataGridColumn via something we call a ProxyElement.

The example below illustrates how to connect a logical child such as ContextMenu or DataGridColumn to the parent View's DataContext

 <Window x:Class="WpfApplicationMultiThreading.Window5"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:vb="http://schemas.microsoft.com/wpf/2008/toolkit"
Title="Window5" Height="300" Width="300" >
<Grid x:Name="MyGrid">
<Grid.Resources>
<FrameworkElement x:Key="ProxyElement" DataContext="{Binding}"/>
</Grid.Resources>
<Grid.DataContext>
<TextBlock Text="Text Column Header" Tag="Tag Columne Header"/>
</Grid.DataContext>
<ContentControl Visibility="Collapsed"
Content="{StaticResource ProxyElement}"/>
<vb:DataGrid AutoGenerateColumns="False" x:Name="MyDataGrid">
<vb:DataGrid.ItemsSource>
<x:Array Type="{x:Type TextBlock}">
<TextBlock Text="1" Tag="1.1"/>
<TextBlock Text="2" Tag="1.2"/>
<TextBlock Text="3" Tag="2.1"/>
<TextBlock Text="4" Tag="2.2"/>
</x:Array>
</vb:DataGrid.ItemsSource>
<vb:DataGrid.Columns>
<vb:DataGridTextColumn
Header="{Binding DataContext.Text,
Source={StaticResource ProxyElement}}"
Binding="{Binding Text}"/>
<vb:DataGridTextColumn
Header="{Binding DataContext.Tag,
Source={StaticResource ProxyElement}}"
Binding="{Binding Tag}"/>
</vb:DataGrid.Columns>
</vb:DataGrid>
</Grid>
</Window>

The view above encountered the same binding error that you have found if I did not have implemented the ProxyElement hack. The ProxyElement is any FrameworkElement that steals the DataContext from the main View and offers it to the logical child such as ContextMenu or DataGridColumn. For that it must be hosted as a Content into an invisible ContentControl which is under the same View.

I hope this guides you in correct direction.

小开

A slightly shorter alternative to using a StaticResource as in the accepted answer is x:Reference:

<StackPanel>


<!--Set the DataContext here if you do not want to inherit the parent one-->
<FrameworkElement x:Name="ProxyElement" Visibility="Collapsed"/>


<DataGrid>
<DataGrid.Columns>
<DataGridTextColumn
Header="{Binding DataContext.Whatever, Source={x:Reference ProxyElement}}"
Binding="{Binding ...}" />
</DataGrid.Columns>
</DataGrid>


</StackPanel>

The main advantage of this is: if you already have an element which is not a DataGrid's ancestor (i.e. not the StackPanel in the example above), you can just give it a name and use it as the x:Reference instead, hence not needing to define any dummy FrameworkElement at all.

If you try referencing an ancestor, you will get a XamlParseException at run-time due to a cyclical dependency.

小开

The way without a proxy is to set bindings in the constructor:

var i = 0;
var converter = new BooleanToVisibilityConverter();
foreach(var column in DataGrid.Columns)
{
BindingOperations.SetBinding(column, DataGridColumn.VisibilityProperty, new Binding($"Columns[{i++}].IsSelected")
{
Source = ViewModel,
Converter = converter,
});
}
小开

The Proxy Element didn't work for me, for a tooltip. For an infragistics DataGrid I did this, you might change it easily to your kind of grid:

<igDP:ImageField Label="_Invited" Name="Invited">
<igDP:Field.Settings>
<igDP:FieldSettings>
<igDP:FieldSettings.CellValuePresenterStyle>
<Style TargetType="{x:Type igDP:CellValuePresenter}">
<Setter Property="ToolTip">
<Setter.Value>
<Label Content="{Binding DataItem.InvitationSent, Converter={StaticResource dateTimeConverter}}"/>
</Setter.Value>
</Setter>
</Style>
</igDP:FieldSettings.CellValuePresenterStyle>
</igDP:FieldSettings>
</igDP:Field.Settings>
</igDP:ImageField>

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