How to Expand and Collapse Items in an MVVM Manner

Environment

Product Version	2022.1.117
Product	RadTreeListView for WPF

Description

How to expand and collapse items via the RadTreeListView control's public methods in an MVVM-friendly manner.

Solution

Using the IsExpandedBinding mechanism of the RadTreeListView can bring some limitations related with the UI virtualization to the forefront. When an item is outside the viewport, setting the IsExpanded properties is only reflected when a container for the item is created in some scenarios.

The public methods exposed by the control can be used in such scenarios to update the UI properly.

Here is how you can use the methods in an MVVM-friendly manner by creating appropriate Action properties:

Define the required Actions

C#

    public class WarehouseViewModel : ViewModelBase
    {
        public Action ExpandAllAction { get; set; }
        public Action CollapseAllAction { get; set; }
        public Action<object> ExpandItemAction { get; set; }
        public Action<object> CollapseItemAction { get; set; }

        public WarehouseViewModel()
        {
        }

        // ...
    }

You can then set these actions as follows:

Use the API of the TreeListView in the Actions

C#

	public MainWindow()
	{
		InitializeComponent();

		var viewModel = new WarehouseViewModel();
		viewModel.ExpandAllAction = () => { this.TreeListView.ExpandAllHierarchyItems(); };
		viewModel.CollapseAllAction = () => { this.TreeListView.CollapseAllHierarchyItems(); };
		viewModel.ExpandItemAction = (item) => { this.TreeListView.ExpandHierarchyItem(item); };
		viewModel.CollapseItemAction = (item) => { this.TreeListView.CollapseHierarchyItem(item); };

		this.DataContext = viewModel;
	}

You can then expose an appropriate method to use inside your viewmodel and also bind it to a command if this is necessary:

Invoke the ExpandItemAction and ExpandAllAction

C#

	public WarehouseViewModel()
	{
		this.ExpandItemCommand = new DelegateCommand(OnExpandItemCommandExecuted);
		this.ExpandAllItemsCommand = new DelegateCommand(OnExpandAllItemsCommandExecuted);
	}

	public void OnExpandItemCommandExecuted(object item)
	{
		(item as WarehouseItem).IsExpanded = true;
		this.ExpandItemAction(item);
	}

	public void OnExpandAllItemsCommandExecuted(object obj)
	{
		foreach (var item in this.WarehouseItems)
		{
			item.IsExpanded = true;
		}

		this.ExpandAllAction();
	}

The collapse actions can be bound in a similar manner.

See Also

• Expanding and Collapsing Items
• UI Virtualization