How can I access the ListViewItems of a WPF ListView?

Question

Within an event, I'd like to put the focus on a specific TextBox within the ListViewItem's template. The XAML looks like this:

<ListView x:Name="myList" ItemsSource="{Binding SomeList}">
    <ListView.View>
        <GridView>
            <GridViewColumn>
                <GridViewColumn.CellTemplate>
                    <DataTemplate>
                        <!-- Focus this! -->
                        <TextBox x:Name="myBox"/>

I've tried the following in the code behind:

(myList.FindName("myBox") as TextBox).Focus();

but I seem to have misunderstood the FindName() docs, because it returns null.

Also the ListView.Items doesn't help, because that (of course) contains my bound business objects and no ListViewItems.

Neither does myList.ItemContainerGenerator.ContainerFromItem(item), which also returns null.

Answer 1

To understand why ContainerFromItem didn't work for me, here some background. The event handler where I needed this functionality looks like this:

var item = new SomeListItem();
SomeList.Add(item);
ListViewItem = SomeList.ItemContainerGenerator.ContainerFromItem(item); // returns null

After the Add() the ItemContainerGenerator doesn't immediately create the container, because the CollectionChanged event could be handled on a non-UI-thread. Instead it starts an asynchronous call and waits for the UI thread to callback and execute the actual ListViewItem control generation.

To be notified when this happens, the ItemContainerGenerator exposes a StatusChanged event which is fired after all Containers are generated.

Now I have to listen to this event and decide whether the control currently want's to set focus or not.

Answer 2

As others have noted, The myBox TextBox can not be found by calling FindName on the ListView. However, you can get the ListViewItem that is currently selected, and use the VisualTreeHelper class to get the TextBox from the ListViewItem. To do so looks something like this:

private void myList_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
    if (myList.SelectedItem != null)
    {
        object o = myList.SelectedItem;
        ListViewItem lvi = (ListViewItem)myList.ItemContainerGenerator.ContainerFromItem(o);
        TextBox tb = FindByName("myBox", lvi) as TextBox;

        if (tb != null)
            tb.Dispatcher.BeginInvoke(new Func<bool>(tb.Focus));
    }
}

private FrameworkElement FindByName(string name, FrameworkElement root)
{
    Stack<FrameworkElement> tree = new Stack<FrameworkElement>();
    tree.Push(root);

    while (tree.Count > 0)
    {
        FrameworkElement current = tree.Pop();
        if (current.Name == name)
            return current;

        int count = VisualTreeHelper.GetChildrenCount(current);
        for (int i = 0; i < count; ++i)
        {
            DependencyObject child = VisualTreeHelper.GetChild(current, i);
            if (child is FrameworkElement)
                tree.Push((FrameworkElement)child);
        }
    }

    return null;
}

Answer 3

I noticed that the question title does not directly relate to the content of the question, and neither does the accepted answer answer it. I have been able to "access the ListViewItems of a WPF ListView" by using this:

public static IEnumerable<ListViewItem> GetListViewItemsFromList(ListView lv)
{
    return FindChildrenOfType<ListViewItem>(lv);
}

public static IEnumerable<T> FindChildrenOfType<T>(this DependencyObject ob)
    where T : class
{
    foreach (var child in GetChildren(ob))
    {
        T castedChild = child as T;
        if (castedChild != null)
        {
            yield return castedChild;
        }
        else
        {
            foreach (var internalChild in FindChildrenOfType<T>(child))
            {
                yield return internalChild;
            }
        }
    }
}

public static IEnumerable<DependencyObject> GetChildren(this DependencyObject ob)
{
    int childCount = VisualTreeHelper.GetChildrenCount(ob);

    for (int i = 0; i < childCount; i++)
    {
        yield return VisualTreeHelper.GetChild(ob, i);
    }
}

I'm not sure how hectic the recursion gets, but it seemed to work fine in my case. And no, I have not used yield return in a recursive context before.