StackLayout

Thursday, June 9th, 2005 at 8:05 am, Swing.
Written by

The more demos I write, the more effects I'd like to reuse for other demos. In some cases I'd like to reuse only a part of an effect. In the application I'm writing, I wanted to use the animated curves from Help Your Shelf. In this demo, there is a CurvePanel extending GradientPanel. My first problem was I wanted to change the gradient and I felt it was awkward to modify the base class rather than just using another implementation. I then added sprites to the demo and I wanted them to be displayed below the curves but on top of the gradient. That's why I decided to decouple every layer and use a StackLayout to produce this:

To achieve this I simply extracted each graphical element into a separate component: CurvesPanel, GradientPanel and AvatarChooser. With the StackLayout it is very easy to stack them in the right order:

JPanel pane = new JPanel();
pane.setLayout(new StackLayout());

GradientPanel gradient = new GradientPanel();
AvatarChooser chooser = new AvatarChooser();
CurvesPanel curves = new CurvesPanel();

pane.add(gradient, StackLayout.TOP);
pane.add(chooser, StackLayout.TOP);
pane.add(curves, StackLayout.TOP);

The API is very simple and let you add a new component either on top or at the bottom of the stack. Here is how the three components are stacked:

The code used to create the layout is very simple. As you can see below, it simply changes the Z order of every component and make them take as much space as possible, thus providing the same behavior than the BorderLayout.CENTER constraint. Here is the source code:

import java.awt.Component;

import java.awt.Container;

import java.awt.Dimension;

import java.awt.Insets;

import java.awt.LayoutManager2;

import java.awt.Rectangle;

import java.util.LinkedList;

import java.util.List;


public class StackLayout implements LayoutManager2 {

    public static final String BOTTOM = "bottom";

    public static final String TOP = "top";


    private List components = new LinkedList();


    public void addLayoutComponent(Component comp, Object constraints) {

        synchronized (comp.getTreeLock()) {

            if (BOTTOM.equals(constraints)) {

                components.add(0, comp);

            } else if (TOP.equals(constraints)) {

                components.add(comp);

            } else {

                components.add(comp);

            }

        }

    }


    public void addLayoutComponent(String name, Component comp) {

        addLayoutComponent(comp, TOP);

    }


    public void removeLayoutComponent(Component comp) {

        synchronized (comp.getTreeLock()) {

            components.remove(comp);

        }

    }


    public float getLayoutAlignmentX(Container target) {

        return 0.5f;

    }


    public float getLayoutAlignmentY(Container target) {

        return 0.5f;

    }


    public void invalidateLayout(Container target) {

    }


    public Dimension preferredLayoutSize(Container parent) {

        synchronized (parent.getTreeLock()) {

            int width = 0;

            int height = 0;


            for (Component comp: components) {

                Dimension size = comp.getPreferredSize();

                width = Math.max(size.width, width);

                height = Math.max(size.height, height);

            }


            Insets insets = parent.getInsets();

            width += insets.left + insets.right;

            height += insets.top + insets.bottom;


            return new Dimension(width, height);

        }

    }


    public Dimension minimumLayoutSize(Container parent) {

        synchronized (parent.getTreeLock()) {

            int width = 0;

            int height = 0;


            for (Component comp: components) {

                Dimension size = comp.getMinimumSize();

                width = Math.max(size.width, width);

                height = Math.max(size.height, height);

            }


            Insets insets = parent.getInsets();

            width += insets.left + insets.right;

            height += insets.top + insets.bottom;


            return new Dimension(width, height);

        }

    }


    public Dimension maximumLayoutSize(Container target) {

        return new Dimension(Integer.MAX_VALUE,

                             Integer.MAX_VALUE);

    }


    public void layoutContainer(Container parent) {

        synchronized (parent.getTreeLock()) {

            int width = parent.getWidth();

            int height = parent.getHeight();


            Rectangle bounds = new Rectangle(0, 0, width, height);


            int componentsCount = components.size();


            for (int i = 0; i 

If you want to develop reusable, non opaque components, this layout can be very handy.


P.S: The white panel is actually used for debugging purpose only.

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