Binding a CollectionViewSource within a DataTempla

问题:

'ContentTemplate' is a DataTemplate that displays an object which has a member 'FooList' (an ObservableCollection).

<DataTemplate x:Key="ContentTemplate">
    <ListBox ItemsSource="{Binding Path=FOO}">
        ...
    </ListBox>
</DataTemplate>

I need to be able to filter that FooList using a CollectionViewSource. This is usually been straight forward but I can't seem to get the binding to work within a DataTemplate. I attempted to this:

<DataTemplate x:Key="ContentTemplate">
    <DataTemplate.Resources>
        <CollectionViewSource x:Key="CVS" Source="{Binding Path=FooList}" Filter="FooFilter"/>
    <DataTemplate.Resources>
    <ListBox ItemsSource="{Binding Source={StaticResource CVS}}">

The errors I get from this is:

System.Windows.Data Error: 2 : Cannot find governing FrameworkElement or FrameworkContentElement for target element. BindingExpression:Path=FooList; DataItem=null; target element is 'CollectionViewSource' (HashCode=52991666); target property is 'Source' (type 'Object')

Which sounds to me like it's looking for 'FooList' on the CollectionViewSource instead of the object bound to the DataTemplate.

So... how do I get this to look at the correct object?

回答1:

As I understand it, the DataTemplate acts as instructions on what to insert into the visual tree but does not become a part of the visual tree itself. I only came to this hypothesis after running into the same problem you've described above. I fixed the issue by attaching the CollectionViewSource to the resources of an element that would be part of the visual tree, in my case a grid. Here is the sample that did work:

<DataTemplate DataType="{x:Type TypedLists:AssetModelListViewModel}">
    <Grid>
        <Grid.Resources>
            <CollectionViewSource x:Key="items"
                                  Source="{Binding}">
                <CollectionViewSource.SortDescriptions>
                    <scm:SortDescription PropertyName="AssetType.AssetCategory.Name" />
                    <scm:SortDescription PropertyName="AssetType.Name" />
                    <scm:SortDescription PropertyName="Manufacturer.Name" />
                </CollectionViewSource.SortDescriptions>
            </CollectionViewSource>
        </Grid.Resources>

        <ListView ItemsSource="{Binding Source={StaticResource items}}">

        </ListView>
    </Grid>
</DataTemplate>

回答2:

I think you need to bind to the view of the CollectionViewSource:

<ListBox ItemsSource="{Binding Path=View, Source={StaticResource CVS}}">

回答3:

I worked around this issue by moving the data template into a user control.