/// <summary>
/// Returns the <see cref="UndoManager"/> defined in the view model or
/// nearest ancestor hierachy.
/// </summary>
/// <exception cref="NotSupportedException">
/// More than one <see cref="UndoManager"/> is defined in the same ancestor level.
/// </exception>
/// <exception cref="InvalidOperationException">
/// Undo is enabled but no <see cref="UndoManager"/> is defined in the view model hierarchy.
/// </exception>
public static UndoManager GetManager(IViewModel vm)
{
IEnumerable <IViewModel> currentLevel = new IViewModel[] { vm };
do
{
var undoRootBehaviors = currentLevel
.Select(x => {
UndoRootBehavior b;
x.Descriptor.Behaviors.TryGetBehavior(out b);
return(new { VM = x, Behavior = b });
})
.Where(x => x.Behavior != null)
.ToArray();
switch (undoRootBehaviors.Length)
{
case 0:
currentLevel = currentLevel
.SelectMany(x => x.Kernel.Parents)
.ToArray();
break;
case 1:
var match = undoRootBehaviors.Single();
return(match.Behavior.GetUndoManager(match.VM.GetContext()));
default:
throw new NotSupportedException(ExceptionTexts.MultipleUndoRoots);
}
} while (currentLevel.Any());
//throw new InvalidOperationException(ExceptionTexts.NoUndoRootManagerFound);
return(null);
}
