Setting TreeView.DataContext doesn't refresh the tree

Question

I have a List that I've bound to a TreeView. Setting TreeView.DataContext works - everything displays correctly. I then change the list (add an item to it) and set TreeView.DataContext again (to the same value) but the tree does not refresh with the new items. How do I get the treeview to refresh?

This is basically my code:

public class xItemCollection : ObservableCollection<xItem>
{
}

public class xItem : INotifyPropertyChanged
{
    xItemCollection _Items;
    string m_Text;

    public xItem()
    {
        _Items = new xItemCollection();
    }

    public xItemCollection Items {get{return _Items;}}
    public string Text {get{return m_Text;} set{m_Text=value;}}
}

class MyProgram
{
    xItem m_RootItem;

    void UpdateTree()
    {
        this.RootItem = new xItem();
        treeView.DataContext = this;
    }

    public xItem RootItem
    {
        get { return m_RootItem;}
        set { m_RootItem = value;}
    }
}

The xaml is:

<TreeView Name="Tree" ItemsSource="{Binding Path=RootItem.Items}" >

<TreeView.ItemTemplate>
    <HierarchicalDataTemplate ItemsSource="{Binding Items}">
        <StackPanel Orientation="Horizontal">
            <TextBlock Text="{Binding Text}" />
        </StackPanel>
    </HierarchicalDataTemplate>
</TreeView.ItemTemplate>
</TreeView>

Adding items to the list works until the tree is rendered for the first time. After it is rendered, adding/removing items does not refresh the tree.

Answer 1

if you assign the same object to a datacontext, I guess it will not fire the datacontext as being changed.

you have some options here:

1. assign null to the datacontext and reassign your list, or call any other "refreshing command" that gets your datacontext refreshed, which is actually a pretty bad idea as your whole tree has to be regenerated.

2. use an ObservableCollection as your list. This automatically triggers a CollectionChanged event if you add an item, that WPF uses to update only the ChangedParts of the list.

I would definatly recommend using the second approach!

Answer 2

I needed to implement INotifyPropertyChanged and then fire PropertyChanged when RootItem changed. My code was creating a new list of items then assigning the complete list to RootItem. Without PropertyChanged the TreeView never knew that RootItem had changed.