Q:

How to expand one node in Silverlight toolkit treeview using MVVM?

How can I expand a node in a treeview using MVVM?
I have a x level treeview and I made my own class to bind it to the TreeView control.
I did manage to set IsSelected property to true when I create the TreeView list. 
So I just have to bind my IsSelected value to the TreeViewItem IsSelected property, but it's not that simple at all...
Here is my class:
public class HierarchicalItem : Model
{
    public string Name { get; set; }
    public int Id { get; set; }

    private bool _IsSelected;
    public bool IsSelected
    {
        get { return _IsSelected; }
        set
        {
            if (_IsSelected != value)
            {
                _IsSelected = value;
                RaisePropertyChanged("IsSelected");
            }
        }
    }

    private ObservableCollection<HierarchicalItem> _children;
    public ObservableCollection<HierarchicalItem> Children
    {
        get
        {
            return _children;
        }
        set
        {
            if (_children != value)
            {
                _children = value;
                RaisePropertyChanged("Children");
            }
        }
    }
}

I tried that with IsSelected and IsExpanded:
<controls:TreeView.ItemContainerStyle>
    <Style TargetType="controls:TreeViewItem">
        <Setter Property="IsSelected" Value="{Binding IsSelected}" />
    </Style>
</controls:TreeView.ItemContainerStyle>

But it returns, that IsSelected and IsExpanded is read only (this works in WPF).
I have looked many solutions for this, but none works for me, because I have dynamic treeviews in a listbox and in each of the treeviews I have to expand the whole path to the node that has a given Id. For example I want to expand all nodes that have Id = 30 in each treeview.

A:

Unfortunately, it is not possible to set bindings on style setters in Silverlight 4.
One way to set IsExpanded, which admittedly isn't all that pretty, is to set the binding on the ToggleButton in the TreeViewItem's control template. If you go to http://msdn.microsoft.com/en-us/library/dd728671(v=vs.95).aspx you can get the default control template for TreeViewItem. You could copy this and replace the following:

with

