How can I make WPF Trigger for IsMouseOver on TreeViewItem NOT affect all parents of the moused-over control?
http://blogs.msdn.com/mikehillberg/archive/2006/09/21/MyTreeViewHelperIsMouseDirectlyOverItem.aspx
this link solved the problem, I did not try the Original Source idea.
<Style TargetType="TreeViewItem">
<Style.Triggers>
<Trigger Property="local:MyTreeViewHelper.IsMouseDirectlyOverItem" Value="True">
<Setter Property="Background" Value="Green" />
</Trigger>
</Style.Triggers>
</Style>
where local:MyTreeViewHelper.IsMouseDirectlyOverItem is attached property
public static class MyTreeViewHelper
{
//
// The TreeViewItem that the mouse is currently directly over (or null).
//
private static TreeViewItem _currentItem = null;
//
// IsMouseDirectlyOverItem: A DependencyProperty that will be true only on the
// TreeViewItem that the mouse is directly over. I.e., this won't be set on that
// parent item.
//
// This is the only public member, and is read-only.
//
// The property key (since this is a read-only DP)
private static readonly DependencyPropertyKey IsMouseDirectlyOverItemKey =
DependencyProperty.RegisterAttachedReadOnly("IsMouseDirectlyOverItem",
typeof(bool),
typeof(MyTreeViewHelper),
new FrameworkPropertyMetadata(null, new CoerceValueCallback(CalculateIsMouseDirectlyOverItem)));
// The DP itself
public static readonly DependencyProperty IsMouseDirectlyOverItemProperty =
IsMouseDirectlyOverItemKey.DependencyProperty;
// A strongly-typed getter for the property.
public static bool GetIsMouseDirectlyOverItem(DependencyObject obj)
{
return (bool)obj.GetValue(IsMouseDirectlyOverItemProperty);
}
// A coercion method for the property
private static object CalculateIsMouseDirectlyOverItem(DependencyObject item, object value)
{
// This method is called when the IsMouseDirectlyOver property is being calculated
// for a TreeViewItem.
if (item == _currentItem)
return true;
else
return false;
}
//
// UpdateOverItem: A private RoutedEvent used to find the nearest encapsulating
// TreeViewItem to the mouse's current position.
//
private static readonly RoutedEvent UpdateOverItemEvent = EventManager.RegisterRoutedEvent(
"UpdateOverItem", RoutingStrategy.Bubble, typeof(RoutedEventHandler), typeof(MyTreeViewHelper));
//
// Class constructor
//
static MyTreeViewHelper()
{
// Get all Mouse enter/leave events for TreeViewItem.
EventManager.RegisterClassHandler(typeof(TreeViewItem), TreeViewItem.MouseEnterEvent, new MouseEventHandler(OnMouseTransition), true);
EventManager.RegisterClassHandler(typeof(TreeViewItem), TreeViewItem.MouseLeaveEvent, new MouseEventHandler(OnMouseTransition), true);
// Listen for the UpdateOverItemEvent on all TreeViewItem's.
EventManager.RegisterClassHandler(typeof(TreeViewItem), UpdateOverItemEvent, new RoutedEventHandler(OnUpdateOverItem));
}
//
// OnUpdateOverItem: This method is a listener for the UpdateOverItemEvent. When it is received,
// it means that the sender is the closest TreeViewItem to the mouse (closest in the sense of the tree,
// not geographically).
static void OnUpdateOverItem(object sender, RoutedEventArgs args)
{
// Mark this object as the tree view item over which the mouse
// is currently positioned.
_currentItem = sender as TreeViewItem;
// Tell that item to re-calculate the IsMouseDirectlyOverItem property
_currentItem.InvalidateProperty(IsMouseDirectlyOverItemProperty);
// Prevent this event from notifying other tree view items higher in the tree.
args.Handled = true;
}
//
// OnMouseTransition: This method is a listener for both the MouseEnter event and
// the MouseLeave event on TreeViewItems. It updates the _currentItem, and updates
// the IsMouseDirectlyOverItem property on the previous TreeViewItem and the new
// TreeViewItem.
static void OnMouseTransition(object sender, MouseEventArgs args)
{
lock (IsMouseDirectlyOverItemProperty)
{
if (_currentItem != null)
{
// Tell the item that previously had the mouse that it no longer does.
DependencyObject oldItem = _currentItem;
_currentItem = null;
oldItem.InvalidateProperty(IsMouseDirectlyOverItemProperty);
}
// Get the element that is currently under the mouse.
IInputElement currentPosition = Mouse.DirectlyOver;
// See if the mouse is still over something (any element, not just a tree view item).
if (currentPosition != null)
{
// Yes, the mouse is over something.
// Raise an event from that point. If a TreeViewItem is anywhere above this point
// in the tree, it will receive this event and update _currentItem.
RoutedEventArgs newItemArgs = new RoutedEventArgs(UpdateOverItemEvent);
currentPosition.RaiseEvent(newItemArgs);
}
}
}
}
This link provided a great solution that worked for me.
Effectively, you can override the ControlTemplate and specify the SourceName
for the IsMouseOver
Setter to just the header portion of the TreeViewItem
. So yes, you are technically moused over both the child and parent TreeViewItems
, but the trigger only fires for the item where the cursor is over the header.