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/// <summary>
/// Behaviour that keeps at least one item in the listbox selected by blocking it's
/// deselection (SelectionChanged event).
///
/// Will not allow for deselection by the user or programatically.
/// Will allow for deselection if the selected item is being removed from the list.
/// When the list is empty no item is selected.
///
/// Only tested with SingleSelection list boxes, should work with others.
/// </summary>
public sealed class KeepOneItemSelectedBehavior : Behavior<ListBox>
{
/// <summary>
/// Called after the behavior is attached to an AssociatedObject.
/// </summary>
/// <remarks>
/// Override this to hook up functionality to the AssociatedObject.
/// </remarks>
protected override void OnAttached()
{
base.OnAttached();
AssociatedObject.SelectionChanged +=AssociatedObjectOnSelectionChanged;
}
/// <summary>
/// Selection changed event handler that prevents the last selected item in the listbox from being deselected.
/// Only tested with SingleSelection list boxes, should work with others.
/// </summary>
/// <param name="sender">ListBox that raised the event.</param>
/// <param name="e">Selection changed information.</param>
private void AssociatedObjectOnSelectionChanged(object sender, SelectionChangedEventArgs e)
{
var listbox = ((ListBox)sender);
if (listbox.SelectedItem == null)
{
if (e.RemovedItems.Count > 0)
{
object itemToReselect = e.RemovedItems[0];
if (listbox.Items.Contains(itemToReselect)) // only reselect if the item is still part of the list.
{
listbox.SelectedItem = itemToReselect;
}
}
}
}
/// <summary>
/// Called when the behavior is being detached from its AssociatedObject, but before it has actually occurred.
/// </summary>
/// <remarks>
/// Override this to unhook functionality from the AssociatedObject.
/// </remarks>
protected override void OnDetaching()
{
base.OnDetaching();
AssociatedObject.SelectionChanged -= AssociatedObjectOnSelectionChanged;
}
}
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