Expand/Collapse TreeView Nodes on Ctrl+LeftMouse in WPF

Question

I want to collapse or expand all TreeView nodes under parent node if user holds down Left Control key and presses left mouse button on expansion arrow of tree view.

How do you do this in WPF? It's not as obvious as it was in WinForms.

Answer 1

<TreeView PreviewMouseLeftButtonDown="TreeView_PreviewMouseLeftButtonDown">

    <TreeViewItem Header="A" >
        <TreeViewItem Header="A-1" />
        <TreeViewItem Header="A-2" >
            <TreeViewItem Header="A-2-a" />
            <TreeViewItem Header="A-2-b" />
            <TreeViewItem Header="A-2-c" />
        </TreeViewItem>
        <TreeViewItem Header="A-3" />
    </TreeViewItem>
    <TreeViewItem Header="B" >
        <TreeViewItem Header="B-1" />
    </TreeViewItem>
    <TreeViewItem Header="C">
        <TreeViewItem Header="C-1" >
            <TreeViewItem Header="C-1-a" />
            <TreeViewItem Header="C-1-b" />
        </TreeViewItem>
    </TreeViewItem>
</TreeView>

　

private void TreeView_PreviewMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
    System.Diagnostics.Debug.WriteLine("PreviewMouseLeftDown");

    if ((Keyboard.Modifiers & ModifierKeys.Control) != ModifierKeys.Control)
    {
        System.Diagnostics.Debug.WriteLine("Not ControlKey Press");
        return;
    }

    var keystate = Keyboard.GetKeyStates(Key.LeftCtrl);
    if (keystate == KeyStates.None)
    {
        System.Diagnostics.Debug.WriteLine("Not Left-ControlKey Press");
        return;
    }

    TreeView tv = (TreeView)sender;
    TreeViewItem tvi = null;
    ToggleButton toggle = null;
    DependencyObject d = e.OriginalSource as DependencyObject;
    while (d != null)
    {
        if (d == sender)
        {
            System.Diagnostics.Debug.WriteLine("Not Found");
            return;
        }
        if (d is ToggleButton)
        {
            toggle = (ToggleButton)d;
        }
        if (d is TreeViewItem)
        {
            tvi = (TreeViewItem)d;
            break;
        }

        d = VisualTreeHelper.GetParent(d);
    }


    if (tvi == null || toggle == null || toggle.TemplatedParent != tvi)
    {
        System.Diagnostics.Debug.WriteLine("Not Found Toggle");
        return;
    }

    if (tvi.IsExpanded)
    {
        System.Diagnostics.Debug.WriteLine("Is Expanded");
        tvi.IsExpanded = false;
    }
    else
    {
        System.Diagnostics.Debug.WriteLine("Is Not Expanded");
        Dispatcher.BeginInvoke(new Action(() =>
        {
            System.Diagnostics.Debug.WriteLine("BeginInvoke");
            tvi.ExpandSubtree();
        }), System.Windows.Threading.DispatcherPriority.Loaded);
    }
    e.Handled = true;
}