get parent-note in treeview when the child-items are the same object

Question

i have a TreeView with same in xaml createt TreeViewItems. And one note has a ObservableCollection as ItemSource. This works like a Charm. But now i want same Notes to every item of the list (for better organization). So i do this:

This is my HierarchicalDataTemplate for the liste

<HierarchicalDataTemplate DataType="{x:Type classes:Connection}" ItemsSource="{Binding Source={StaticResource ConnectionChilds}}" >
    <TextBlock Text="{Binding DisplayName}" />
</HierarchicalDataTemplate>

And the ItemsSource:

<collections:ArrayList x:Key="ConnectionChilds">
    <classes:TreeItemObject ItemsSourcePath="Child1" />
    <classes:TreeItemObject ItemsSourcePath="Child2" />
    <classes:TreeItemObject ItemsSourcePath="Child3" />
</collections:ArrayList>

TreeItemObject is a simple Class:

public class TreeItemObject
{
    public string ItemsSourcePath { get; set; }
}

And last but not least HierarchicalDataTemplate for TreeItemObject:

<DataTemplate DataType="{x:Type classes:TreeItemObject}">
    <TextBlock Margin="5,0" Text="{Binding Path=ItemsSourcePath}"/>
</DataTemplate>

Looked like this

Connection 1
    Child1
    Child2
    Child3
Connection 2
    Child1
    Child2
    Child3
Connection 3
    Child1
    Child2
    Child3

Works perfekt. But now if i select "Connection 2\Child3" i got the same object like "Connection 1\Child3" or "Connection 3\Child3". Ok make sense because based on same object. With that situation i have no chance to find out the parent-note on OnSelectedItemChanged.

Because if i search with this extension-Class. I only get the first expanded Connection-Note.

http://social.msdn.microsoft.com/Forums/silverlight/en-US/84cd3a27-6b17-48e6-8f8a-e5737601fdac/treeviewitemcontainergeneratorcontainerfromitem-returns-null?forum=silverlightnet

Is there a way to find the real parent in the TreeView?

Mark Travis Mark Travis · Accepted Answer · 2013-12-23T13:50:00

I personally do not like the idea of creating clones within a converter but I do not know the full scope of your problem. So working with what you have presented here, we can achieve the assignment of a parent to each TreeItemObject via a MultiValueConverter.

WPF has an awesome feature called MultiBinding. It processes 1 or more source values into a single target. To do this, it needs a multivalue converter.

So, change the TreeItemObject to

public class TreeItemObject
{
    public string ItemsSourcePath { get; set; }
    public WeakReference Parent { get; set; }
}

The hierarchicalDataTemplate for the Connection type would become

<HierarchicalDataTemplate DataType="{x:Type classes:Connection}">
    <HierarchicalDataTemplate.ItemsSource>
        <MultiBinding Converter="{StaticResource items2Clones}">
            <Binding Source="{StaticResource ConnectionChilds}" />
            <Binding />
        </MultiBinding>
    </HierarchicalDataTemplate.ItemsSource>
    <TextBlock Text="{Binding DisplayName}" />
</HierarchicalDataTemplate>

Based on the above binding, to set the parent in the converter, the Convert method in your convert will be along the lines

public object Convert(object[] values, Type targetType, object parameter, System.Globalization.CultureInfo culture)
{
    var destinationItems = new Collection<TreeItemObject>();

    var items = values[0] as Collection<TreeItemObject>;
    var parent = values[1] as Connection;

    // null checks are required here for items and parent

    foreach (var item in items)
    {
        var destinationItem = item.Clone(); // Assumed extension method
        destinationItem.Parent = new WeakReference(parent);
        destinationItems.Add(destinationItem);
    }

    return destinationItems;
}

Finally, the SelectedItemChanged event handler would be something like

private void TreeView_OnSelectedItemChanged(object sender, RoutedPropertyChangedEventArgs<object> e)
{
    var item = (TreeItemObject)e.NewValue;
    if ((item != null) && (item.Parent != null) && (item.Parent.IsAlive))
    {
        // do stuff - Console.WriteLine(((Connection)item.Parent.Target).DisplayName);
    }
}

I have removed exception management and some null checking for brevity.

I hope this helps

get parent-note in treeview when the child-items are the same object

3 Answers