Thursday, November 04, 2010

Forcing open a WPF ContextMenu

I had this control where a button was displaying a ContextMenu. I wanted to keep the ContextMenu open so I can manipulate its content. I had assumed that the StaysOpen property would do that for me; it did not. Also, I tried using a ContextMenuClosing event approach, only to discover that it is one of those rare "ing" events that doesn't have a Cancel property. I've looked in the sources of ContextMenu and Popup to see just what is going on and I have decided that the design was impossible to patch in order to get the behaviour I wanted.

In the end, the only solution I could find was to inherit from ContextMenu into a new class that would coerce the IsOpen property to true when StaysOpen is set to true. That did the trick. Here is the code:

public class StaysOpenContextMenu:ContextMenu
{
static StaysOpenContextMenu()
{
fixContextMenuStaysOpen();
}

private static void fixContextMenuStaysOpen()
{
IsOpenProperty.OverrideMetadata(
typeof(StaysOpenContextMenu),
new FrameworkPropertyMetadata(false, null,coerceIsOpen));
StaysOpenProperty.OverrideMetadata(
typeof(StaysOpenContextMenu),
new FrameworkPropertyMetadata(false, null, coerceStaysOpen));
}

private static object coerceStaysOpen(DependencyObject d, object basevalue)
{
d.CoerceValue(IsOpenProperty);
return basevalue;
}

private static object coerceIsOpen(DependencyObject d, object basevalue)
{
ContextMenu menu = (ContextMenu)d;
if (menu.StaysOpen)
{
return true;
}
return basevalue;
}

}


Hope it helps people out.

Update:

This solution only works for the body of the ContextMenu, the submenus are something else. However, the submenus are defined in the control template of a menu item, so that can be easily remedied by changing it to your needs. One quick and dirty solution would be to add a trigger that sets the IsSubMenuOpen property to true whenever StaysOpenOnClick is set. Or, if you simply want to freeze a menu in place, change the template so that the mouse click or hover will only trigger IsSubMenuOpen when the parent ContextMenu has StaysOpen to false, while the StaysOpen property of the MenuItem Popup is set to the ContextMenu StaysOpen.

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