How can I cancel a user's WPF TreeView click?

Question

I\'ve got a WPF application with a Treeview control.

When the user clicks a node on the tree, other TextBox, ComboBox, etc. controls on the page are populated with a

Answer 1

You can't cancel the event like you can, for example, a Closing event. But you can undo it if you cache the last selected value. The secret is you have to change the selection without re-firing the SelectionChanged event. Here's an example:

    private object _LastSelection = null;
    private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
    {
        if (IsUpdated)
        {
            MessageBoxResult result = MessageBox.Show("The current record has been modified. Are you sure you want to navigate away? Click Cancel to continue editing. If you click OK all changes will be lost.", "Warning", MessageBoxButton.OKCancel, MessageBoxImage.Hand);
            switch (result)
            {
                case MessageBoxResult.Cancel:
                    e.Handled = true;
                    // disable event so this doesn't go into an infinite loop when the selection is changed to the cached value
                    PersonListView.SelectionChanged -= new SelectionChangedEventHandler(OnSelectionChanged);
                    PersonListView.SelectedItem = _LastSelection;
                    PersonListView.SelectionChanged += new SelectionChangedEventHandler(OnSelectionChanged);
                    return;
                case MessageBoxResult.OK:
                    // revert the object to the original state
                    LocalDataContext.Persons.GetOriginalEntityState(_LastSelection).CopyTo(_LastSelection);
                    IsUpdated = false;
                    Refresh();
                    break;
                default:
                    throw new ApplicationException("Invalid response.");
            }
        }

        // cache the selected item for undo
        _LastSelection = PersonListView.SelectedItem;
    }