gef : change child constraint to a new parent

Question

i have somme process elements that can contain other process elements with no limit.

i managed the addition of new process into other directly from the palette, it works right but when i drag a process already drawn to integrate it as a new child of another process already drawn, the editor don't let me do so and i have a white cross cursor.

in my model the Process class is extending ContainerElement class wich handles the addition and removal of children and the notification stuff.

i was thinking that since the process will have a new parent i must add this in the change ConstraintCommand

here's a snippet of my code

    public class ProcessFigure extends Figure {
    public ProcessFigure() {
    setLayoutManager(new XYLayout());

    ellipse = new Ellipse();
    ellipse.setFill(false);
    add(ellipse);
    label = new Label();
    add(label);
    ellipse.setLayoutManager(new XYLayout());
   }

    public IFigure getContentPane() {
    return ellipse;
   }
    ...
}

 ------------------------------
 public class ProcessEditPart extends ContainerElementEditPart {
 ...
    public IFigure getContentPane() {
    return ((ProcessFigure)getFigure()).getContentPane();
    }

    @Override
    protected void createEditPolicies() {
    installEditPolicy(EditPolicy.LAYOUT_ROLE, new ContainerElementXYLayoutEditPolicy(
            (XYLayout) getContentPane().getLayoutManager()));
    }
...
}
------------------------

public class ContainerElementXYLayoutEditPolicy extends XYLayoutEditPolicy {
    ...
    public ContainerElementXYLayoutEditPolicy(XYLayout layoutManager) {
    super();
    setXyLayout(layoutManager);
    }

    private Command getProcessCreateCommand(CreateRequest request) {
    ProcessCreateCommand result = new ProcessCreateCommand();
    Rectangle constraint = (Rectangle) getConstraintFor(request);
    result.setLocation(constraint.getLocation());
    result.setProcess((Process)request.getNewObject());
    result.setParent((ContainerElement)getHost().getModel());
    return result;
    }


    protected Command createChangeConstraintCommand (ChangeBoundsRequest request,EditPart child , Object constraint) {
    ProcessChangeConstraintCommand changeConstraintCommand = new ProcessChangeConstraintCommand (); 
    changeConstraintCommand.setProcess((Process)child.getModel());
    changeConstraintCommand.setNewConstraint((Rectangle)constraint);
    return changeConstraintCommand;

    }    
...

}

i think the problem is that gef can't figure the appropriate layout manager, i tried several changes but get everytime cast or stackoverflow exception, please help !

Answer 1

When you drag an element outside the figure of an edit part GEF fires a REQ_ORPHAN request that must be handled by the edit part from which the element is taken out. If this is not done, I think you can't take the element outside the edit part's figure. You can handle this requires by overriding the getOrphanChildrenCommand in the LayoutEditPolicy class.

I have never used this feature, but this is what is written in the Moving and Resizing of the GEF Programmer's Guide