Have TreeView update its SelectedItem when programmatically changed

Question

In WPF I have a TreeView control where a particular item can be selected either by the user selecting the item directly in the tree view or by clicking on a screen control. The tree view is displaying a list of elements that are being displayed on a user defined form, basically a form designer application.

Here is my problem. When the user clicks on a screen control it calls a method that returns the TreeViewItem that represents the element. It then sets the IsSelected property to true for this element. It correctly changes the visual indicator in the TreeView and it raised the SelectedItemChanged event in the TreeView. This is all good.

However, it appears that somewhere behind the scenes the TreeView still thinks the previous item is selected. Here is why I have come to this conclusion. If I select ElementA by clicking on it in the TreeView is it correctly selected. If I then select ElementB by clicking on the screen control and programmatically setting the IsSelected property for the ElementB TreeViewItem it appears to have selected it correctly. Now if I select ElementA again by clicking on it in the TreeView it does nothing. The SelectedItemChanged event is not raised and the reverse selection box that indicates the selected item stays on ElementB. If I click on ElementB in the TreeView it also does not raise the SelectedItemChanged event, however it does not appear to update the internal flag since if I then click on ElementA on the TreeView it processes it correctly and raises the event.

The only workaround that I have found for this is in the SelectedItemChanged event handler to call the Focus method for the now selected TreeViewItem. If I do this I get the expected behaviour when I select screen controls and programmatically change the selected TreeViewItem.

This is not an acceptable solution though as it creates focus change flicker. When I select items on my form window the focus goes to the TreeView control and then back to the form, causing flicker and slight delay.

Anyone have any indeas.

Update

As requested here is some code. Here is my method of my Explorer window which is the manager of the TreeView in question.

    public bool SelectItemByName(String controlName)
    {
        bool fReturn = false;
        TreeViewItem tviToSelect = FindItemByName(_tviMaster, controlName);
        if (tviToSelect != null && _tviSelectedItem != tviToSelect)
        {
            tviToSelect.IsSelected = true;

            // Make sure the selected item is visible in the TreeView by expanding all of the parent nodes
            ExpandAllParents(tviToSelect);

            tviToSelect.BringIntoView();

            fReturn = true;
        }
        return fReturn;
    }

Every element has a unique identifier that I use as a cross reference between different areas of the interface. When you click a screen control it uses its identifier to find the cooresponding TreeViewItem in the TreeView. Then this code sets it as selected.

Then in my SelectedItemChanged event handler I had to include the following line.

                _tviSelectedItem.Focus();

This fixes my initial issue but introducing the unwant screen flicker.

To recap, I select ElementA in the TreeView directly, then select one or more other elements in the form designer which in turn calls SelectItemByName to programatically set the selected item. All visual indicators show that this worked. In the TreeView the highlighted item changes to the new item that is selected. After selecting any number of elements through the form designer interface if you select ElementA by clicking on it directly in the TreeView it does nothing. It does not get highlighted and it does not fire the SelectedItemChanged event. If you inspect the SelectedItem and SelectedValue properties of the TreeView they all correctly coorespond to the item that was programmatically selected. However, the control somewhere appears to think that ElementA is still selected and doesn't recognize that the selection is changing.

I cannot believe that other people haven't run into this. It appears to be a significant flaw in the TreeView contol in WPF. Not sure if WinForms has the same issue or not.

Rachel Rachel · Accepted Answer · 2011-11-23T15:52:10

Each TreeViewItem has an IsSelected property, and I suspect the old one isn't getting set to false. Try setting it to false whenever you set the new item to true.

var currentItem = treeView.ItemContainerGenerator
    .ContainerFromItem(treeView.SelectedItem) as TreeViewItem;
currentItem.IsSelected = false;

If that doesn't work, try setting focus on the newly selected item at the same time as when you select it. Don't forget that WPF also has two focus scopes: Logical Focus and Keyboard Focus. You may need to set both.

treeViewItem.Focus();         // Sets Logical Focus
Keyboard.Focus(treeViewItem); // Sets Keyboard Focus

Have TreeView update its SelectedItem when programmatically changed

1 Answers