How do I implement drag drop in treeviews that are bound to multiple view models?

[Paqi]

Hi,

I have a TreeView that is bound to multiple view models (different levels of the tree are bound to these models through the use of HierarchicalDataTemplates I list under TreeView.Resources). I found this model here:

http://www.codeproject.com/Articles/26288/Simplifying-the-WPF-TreeView-by-Using-the-ViewMode

I'd love to be able to implement this drag/drop pattern so that I can drag items across two different instances of this tree. I'm having trouble doing so though, because I can’t seem to add attachable properties to my HierarchicalDataTemplate definitions. 

Here's my XAML:

        <TreeView ItemsSource="{Binding Directories}"

                  dd:DragDrop.IsDragSource="True"

                  dd:DragDrop.IsDropTarget="True">

            <TreeView.ItemContainerStyle>

                <!-- bind TreeViewItem to TreeViewItemViewModel-->

                <Style TargetType="{x:Type TreeViewItem}">

                    <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />

                    <Setter Property="IsSelected" Value="{Binding IsSelected, Mode=TwoWay}" />

                    <Setter Property="FontWeight" Value="Normal" />

                    <Style.Triggers>

                        <Trigger Property="IsSelected" Value="True">

                            <Setter Property="FontWeight" Value="Bold" />

                        </Trigger>

                    </Style.Triggers>

                </Style>

            </TreeView.ItemContainerStyle>

            <TreeView.Resources>

                <HierarchicalDataTemplate

                    DataType="{x:Type local:DirectoryViewModel}"

                    ItemsSource="{Binding Children}"

                          <!-I'd like to set  dd:DragDrop.IsDragSource/Target to true here, but the dd namespace isn't recognized here--> 

                    >

                    <StackPanel Orientation="Horizontal">

                        <TextBlock Text="{Binding Name}" />

                    </StackPanel>

                </HierarchicalDataTemplate>

                <HierarchicalDataTemplate

                    DataType="{x:Type local:WorkspaceFileViewModel}"

                    ItemsSource="{Binding Children}"

                          <!-I'd like to set  dd:DragDrop.IsDragSource/Target to true here, but the dd namespace isn't recognized here--> 

                    >

                    <StackPanel Orientation="Horizontal">

                         <TextBlock Text="{Binding Name}" />

                    </StackPanel>

                </HierarchicalDataTemplate>

                <HierarchicalDataTemplate

                    DataType="{x:Type local:WorkspaceFileElementViewModel}"

                    ItemsSource="{Binding Children}"

                           <!-I'd like to set  dd:DragDrop.IsDragSource/Target to true here, but the dd namespace isn't recognized here--> 

                    >

                    <StackPanel Orientation="Horizontal">

                        <TextBlock Text="{Binding Label}" />

                    </StackPanel>

                </HierarchicalDataTemplate>

            </TreeView.Resources>

[robert....@gmail.com]

So, this is a silly question that betrayed my lack of understanding about how attached properties work. That top portion:

<TreeView ItemsSource="{Binding Directories}"

                  dd:DragDrop.IsDragSource="True"

                  dd:DragDrop.IsDropTarget="True">

is all I needed. So long as every view model that's listed in the HierarchicalDataTemplates implements IsDragSource and IsDragTarget, those methods will be called at the appropriate time, because those sub-levels inherit the attached property. 

[robert....@gmail.com]

It appears this isn't enough. I thought it was working, but it turns out the default drop handlers where being used instead of the ones I defined in my various view models. This is because it's looking for a drag drop handler in the view model that's bound to the tree, and I had only defined the interface on the view models I listed in the HierarchicalDataTemplate. I believe my solution will involve using Multibinding and a MultiValueConverter. I'll post my solution when I come up with it.