Why are the GEF children not drawn when removing absolute size of container?

I try to get a simple working GEF editor. I have a GraphicalEditorWithPalette that creates my example model. I have a RootEditPart that overrides createFigure and getModelChildren like this:

public class RootEditPart extends AbstractGraphicalEditPart {
    @Override
    protected IFigure createFigure() {
        Figure figure = new Figure();
        figure.setOpaque(true);
        figure.setLayoutManager(new XYLayout());
        figure.setSize(1000, 1000);
        return figure;
    }
    @Override
    protected List<Positionable> getModelChildren() {
        return getModel().getChildren();
    }
    // More methods ...
}

I have a ChildEditPart that creates a label and override refreshVisuals like this:

public class ChildEditPart extends AbstractGraphicalEditPart {
    @Override
    protected void refreshVisuals() {
        RDC rdc = getModel();
        Label nameLabel = (Label) getFigure();
        nameLabel.setText(rdc.getName());
        Point position = rdc.getPosition();

        Rectangle r = new Rectangle(position.x, position.y, -1,-1);
        ((GraphicalEditPart) getParent()).setLayoutConstraint(this, nameLabel, r);
    }
    // More methods ...
}

This works as expected. But I don't want to have a fixed size for the container. Instead I try to achieve that the containers size adapts to the children. If I remove the figure.setSize(1000, 1000); the children are not drawn any more. What is my mistake?

Edit: Maybe it is important to know that my editor configures the root edit part like this: viewer.setRootEditPart(new ScalableFreeformRootEditPart());

Edit2: Seems like in fact the call viewer.setRootEditPart(new ScalableFreeformRootEditPart())开发者_Python百科; is the problem. If I remove this it works as expected. Currently I don't fully understand why ... would be great if someone could explain.

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You have to set size of parent's figure manually when it needed.

figure.setSize(figure.getPreferredSize());

figure delegates computing it's prefer size to it's layout(if exist). XYLayout will compute minimal size to represent contents.

I think best place to insert this code is setLayoutConstraint of parent EditPart.