Menu click event object parameter references menu, not underlying object - wpf

Question

I added a Line with C# code to my canvas, along with a context menu and attached event. I would like to rotate the Line using a context menu choice, not the menu text in the context menu:
newMenuItem1.PreviewMouseDown += new MouseButtonEventHandler((sx, ex) => {
MenuItem menuItem = (MenuItem)sx;
string theHeader = menuItem.Header.ToString();
if (theHeader.Contains("90")) {
Line ow = ex.Source as Line;
rt = new RotateTransform(90, 25, 50);
ow.RenderTransform = rt;
}
});
This code produces a null reference exception. If I substitute:
UIElement ow = ex.Source as UIElement;
The actual menu text will rotate!
Edit:
Here is more code, I am now trying originalsource too:
private void button1_Click(object sender, RoutedEventArgs e)
{
Line g = new Line();
g.Stroke = System.Windows.Media.Brushes.LawnGreen;
g.X1 = 0; g.X2 = 100;g.Y1 = 0;g.Y2 = 0;
g.HorizontalAlignment = HorizontalAlignment.Left;
g.VerticalAlignment = VerticalAlignment.Center;
g.StrokeThickness = 6;
ContextMenu k = new ContextMenu();
g.ContextMenu = k;
MenuItem newMenuItem1 = new MenuItem();
MenuItem newMenuItem2 = new MenuItem();
MenuItem newMenuItem3 = new MenuItem();
newMenuItem1.Header = "Rotate 90";
newMenuItem2.Header = "Rotate 180";
newMenuItem3.Header = "Rotate 270";
newMenuItem1.PreviewMouseDown += new MouseButtonEventHandler((sx, ex) => {
MenuItem menuItem = (MenuItem)sx;
string theHeader = menuItem.Header.ToString();
if (theHeader.Contains("90")) {
Line ow = (Line)ex.OriginalSource;
rt = new RotateTransform(90, 25, 50);
ow.RenderTransform = rt;
}
});
g.ContextMenu.Items.Add(newMenuItem1);
g.ContextMenu.Items.Add(newMenuItem2);
g.ContextMenu.Items.Add(newMenuItem3);
Canvas.SetTop(g, 18);
Canvas.SetLeft(g, 18);
MyCanvas.Children.Add(g);
///////
I also tried:
private static T FindAncestor<T>(DependencyObject current)
where T : DependencyObject
{
do
{
if (current is T)
{
return (T)current;
}
current = VisualTreeHelper.GetParent(current);
}
while (current != null);
return null;
}
but it does not work. My next plan is to get coordinates off the canvas, and try to determine what control sits there. This will become tricky though if an object is transformed, because I believe the UI sees it at the original position. I've experimented with other controls as well, like the TextBox and get similar issues.

Answer 1

A really quick and dirty way to do this would be to add your line to the menu item's tag property and retrieve it in the PreviewMouseDown handler
When creating your context menu:
newMenuItem1.Tag = g;
In you handler:
Line ow = ((FrameworkElement)ex.Source).Tag as Line;
The less quick and dirty way to do this would be to use the ContextMenuOpening event on your line as that should be sent with the sender equal to the control itself. You could then store a reference to the line somewhere and retrieve it again in the menu item click event. This works better when you have multiple lines (which I'm guess is what you intend) and just one context menu (instead of producing a bunch of copies of the same menu as you are doing now).