Question

I’m using a hierarchical tree view in Silverlight 4. This tree can be cleared and rebuilded quite often, depending on the user’s actions. When this happends, the tree is collapsed by default, which can be annoying from a user perspective.

So, I want to somehow save which nodes are expanded so I can restore the visual state of my tree after it is clear and reloaded.

My treeview is implemented like this:

xmlns:controls="clr-namespace:System.Windows.Controls;assembly=System.Windows.Controls"
xmlns:controls2="clr-namespace:System.Windows;assembly=System.Windows.Controls"

<controls:TreeView x:Name="Tree"
    ItemsSource="{Binding Source={StaticResource ViewModel}, Path=TreeStructure, Mode=OneWay}"
    ItemTemplate="{StaticResource hierarchicalTemplate}" />

<controls2:HierarchicalDataTemplate x:Key="hierarchicalTemplate" ItemsSource="{Binding Children}">
        <TextBlock Text="{Binding Value.DisplayName}">
</controls2:HierarchicalDataTemplate>

ItemsSource of my treeview is bound on an ObservableCollection TreeStructure;

Node is a wrapper class that looks like that:

public class Node
{
    public object Value { get; private set; }

    public ObservableCollection<Node> Children { get; private set; }

    public Node(object value)
    {
        Value = value;
        Children = new ObservableCollection<Node>();
    }
 }

Pretty standard stuff. I saw some solutions for WPF, but I can find anything for the Silverlight tree view…

Any suggestions?

Thanks!

Answer 1

Given the way you are implementing your data as a tree, why not bind the ‘TreeViewItem.IsExpanded` dependency property to a bool property on your own Node?

It will need to be an INotifyPropertyChanged property at a minimum so Node will need to implement INotifyPropertyChanged.

In Silverlight 5 you can just set a style like this to bind to the IsExpanded property:

<Style TargetType="sdk:TreeViewItem" x:Key="itemStyle">
    <Setter Property="IsExpanded" Value="{Binding IsExpanded, Mode=TwoWay}" />
</Style>

And use with

ItemContainerStyle="{Binding Source={StaticResource itemStyle}}"

In Silverlight 4 there are a number of workarounds.