Question

This code throws an error:

    if (modalMessage != null && contains(modalMessage))
    {
        removeChild(modalMessage); // the error is here
        modalMessage = null;            
    }

The Error is:

[Fault] exception, information=ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.

how can this be? i am checking if it is a child beforehand.

Answer 1

contains() will return true if the subject is a descendant of the caller. This will return true for indirect descendants too, children of children etc.

Determines whether the specified display object is a child of the DisplayObjectContainer instance or the instance itself. The search includes the entire display list including this DisplayObjectContainer instance. Grandchildren, great-grandchildren, and so on each return true.

http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/display/DisplayObjectContainer.html#contains%28%29

You could check the parent:

if(modalMessage && modalMessage.parent && modalMessage.parent == this)

Or, for a more general purpose disposal solution:

if(modalMessage) {
    if(modalMessage.parent) DisplayObjectContainer(modalMessage.parent).removeChild(modalMessage);
    modalMessage = null;
}