How to find out the size of a node before it is shown?

Question

Hi,
I am trying to anchor two nodes (say A & B) to the top of an anchor pane such that B is laid out below A. To accomplish this, I need to provide an anchor offset for the control B, which has to be height of the node A. However, as the containing Stage has not been shown yet, the A's node getWidth() method returns 0 (zero). Since, node A's size is computed based on its contents, I can't hardcode its size. So, I am at a loss how to provide the height of the node A in a dynamic manner.
Please feel free to ask me to clarify the question if I didn't make myself clear enough.
Thanks.

Answer 1

If one of the existing layouts doesn't work for you, then you can create your own. A little bit harder to do, but this would be your best bet since there is no trickery involved. Basically, all you have to do is override the layoutChildren() and the computePrefXXX (and, perhaps computeMinXXX) methods from Parent.
Here is any overly simplified example that lays out three circles like a traffic light:
    @Override
    public void start(final Stage stage) {
        Parent parent = new Parent() {
                getChildren().addAll(
                    CircleBuilder.create().fill(Color.RED).radius(20).build(),
                    CircleBuilder.create().fill(Color.YELLOW).radius(20).build(),
                    CircleBuilder.create().fill(Color.GREEN).radius(20).build()
            @Override protected void layoutChildren() {
                double dx = 0;
                double dy = 0;
                for(int n=0, nMax=getChildren().size(); n<nMax; n++) {
                    Node child = getChildren().get(n);                   
                    double prefHeight = child.prefHeight(-1);
                    dy = prefHeight * n + prefHeight / 2;
                    child.setLayoutY(dy);
                    dx = child.prefWidth(-1) / 2;
                    child.setLayoutX(dx);
            @Override
            protected double computePrefHeight(double width) {
                double prefHeight = 0;
                for(Node child : getChildren()) {
                    prefHeight += child.prefHeight(width);
                return prefHeight;
            @Override
            protected double computePrefWidth(double height) {
                return getChildren().get(0).prefWidth(height);
        Scene scene = new Scene(parent);
        stage.setScene(scene);
        stage.show();
    }