Listbox item as Listbox should clear the selection of its item when other item's item is selected?

Question

I have a ListBox as a ListboxItem in the mainlist. In one item that is ListBox I select an item. This selection should be cleared when I have another item selected from the other items ListBox. Code is as below:

Anand Murali · Accepted Answer

You can explicitly null the SelectedItem whenever the ListBox loses focus, i.e you have to handle the LostFocus event.

You could add the event handler to the ListBox and handle the event in the code behind.

XAML Change:

Code Behind:

    private void lstMsgs_LostFocus(object sender, RoutedEventArgs e)
    {
        ListBox listBox = sender as ListBox;
        if (listBox != null)
        {
            listBox.SelectedItem = null;
        }
    }

Method 2:

You could achieve the same result by using a DependencyProperty to handle the LostFocus event.

ListBoxExtension.cs

using System.Windows;
using System.Windows.Controls;

namespace WpfApplication1
{
    public static class ListBoxExtension
    {
        public static readonly DependencyProperty NullSelectedItemOnLostFocusProperty =
            DependencyProperty.RegisterAttached("NullSelectedItemOnLostFocus", typeof(bool), typeof(ListBoxExtension), new UIPropertyMetadata(false, OnNullSelectedItemOnLostFocusChanged));

        public static bool GetNullSelectedItemOnLostFocus(DependencyObject d)
        {
            return (bool)d.GetValue(NullSelectedItemOnLostFocusProperty);
        }

        public static void SetNullSelectedItemOnLostFocus(DependencyObject d, bool value)
        {
            d.SetValue(NullSelectedItemOnLostFocusProperty, value);
        }

        private static void OnNullSelectedItemOnLostFocusChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            bool nullSelectedItemOnLostFocus = (bool)e.NewValue;

            ListBox listBox = d as ListBox;
            if (listBox != null)
            {
                if (nullSelectedItemOnLostFocus)
                    listBox.LostFocus += NullSelectedItem;
                else
                    listBox.LostFocus -= NullSelectedItem;
            }
        }

        public static void NullSelectedItem(object sender, RoutedEventArgs e)
        {
            ListBox listBox = sender as ListBox;
            if (listBox != null)
            {
                listBox.SelectedItem = null;
            }
        }
    }
}

XAML Change 1: Add namespace in which the ListBoxExtension class is present - xmlns:loc="clr-namespace:WpfApplication1"

XAML Change 2: Changing the DependencyProperty - loc:ListBoxExtension.NullSelectedItemOnLostFocus="True"

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