Detecting when JSplitPane divider is being dragged, not component being resized

Question

I want to implement a JSplitPane (horizontal split) where the right component has a constant width i.e. when the divider is dragged it will jump back to the correct size, unless the divider is dragged far enough right in which case the right most component will have zero width.

To re-display the right component the user can then drag the divider far enough to the left.

I've got this mostly working, but when I resize the window depending on how much and how fast I change the window size the divider jumps reveal or hide the right component, where as what I want is that it should not change 'state' ie if the right component was not visible then it should remain invisible and vice versa.

I've tried heaps of things but the main obstacle is that there seems to be no way of knowing weather the divider was dragged by the user via mouse or if the code (my divider logic and/or JSplitPane internal logic) changed the divider position.

Here is a self contained test case, run it and try to drag the horizontal divider to hide and reveal the right side panel and with those hidden/shown try to resize the window.

Does not work as intended on Mac OS X Java 1.6 (Apple) or Java 7 (Oracle). With the Oracle stuff the rendering is much slower and the problem is more severe. Resizing the window slowly works, but fast window size changes cause problems.

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ComponentEvent;
import java.awt.event.ComponentListener;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;

import javax.swing.*;

import net.miginfocom.swing.MigLayout;

public class SplitTest {
    public static class MySplitPane extends JSplitPane {
        boolean m_RightCollapsed;

        public MySplitPane(int orientation, JComponent left, JComponent right) {
            super(orientation, left, right);

            addPropertyChangeListener(new PropertyChangeListener() {

                @Override
                public void propertyChange(PropertyChangeEvent evt) {

                }
            });
            addComponentListener(new ComponentListener() {

                @Override
                public void componentShown(ComponentEvent e) {
                    reposDivider();
                }

                @Override
                public void componentResized(ComponentEvent e) {
                    reposDivider();
                }

                @Override
                public void componentMoved(ComponentEvent e) {
                    reposDivider();
                }

                @Override
                public void componentHidden(ComponentEvent e) {
                }
            });

        }

        public void reposDivider() {
            setDividerLocation(getDividerLocation());
        }

        public void setDividerLocation(int location) {
            int newLocation;
            m_RightCollapsed = location > getSize().width - getRightComponent().getPreferredSize().width / 2;
            if (m_RightCollapsed)
                newLocation = getSize().width;
            else
                newLocation = getSize().width - getInsets().right - getDividerSize() - getRightComponent().getPreferredSize().width;
            super.setDividerLocation(newLocation);
        }
    }
    static class MyScrollable extends JPanel implements Scrollable {
        int m_Height;

        public MyScrollable(int height) {
            m_Height = height;
        }

        @Override
        public void paint(java.awt.Graphics g) {
            super.paint(g);
            g.setColor(Color.CYAN);
            g.fillOval(0, 0, getWidth(), 500);
        }

        @Override
        public Dimension getPreferredScrollableViewportSize() {
            //return super.getPreferredSize();
            return new Dimension(100, m_Height);
        }

        @Override
        public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) {
            // TODO Auto-generated method stub
            return 10;
        }

        @Override
        public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) {
            return 20;
        }

        @Override
        public boolean getScrollableTracksViewportWidth() {
            return true;
        }

        @Override
        public boolean getScrollableTracksViewportHeight() {
            return false;
        }

    }

    public static class ShrinkGrow extends JPanel {
        public ShrinkGrow(final JComponent component, final JSplitPane split) {
            JButton grow = new JButton("+++");
            JButton shrink = new JButton("---");
            add(grow);
            add(shrink);

            grow.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    Dimension oldSize = component.getPreferredSize();
                    Dimension newSize = new Dimension(oldSize.width, oldSize.height + 10);
                    component.setPreferredSize(newSize);
                    component.setSize(newSize);
                }
            });
            shrink.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    Dimension oldSize = component.getPreferredSize();
                    Dimension newSize = new Dimension(oldSize.width, oldSize.height - 10);
                    component.setPreferredSize(newSize);
                    component.setSize(newSize);
                }
            });
        }
    }

    public static void main(String[] args) {
        JFrame window = new JFrame();

        JPanel mainView = new JPanel();
        JPanel top = new JPanel();
        top.setLayout(new BoxLayout(top, BoxLayout.Y_AXIS));
        JPanel bottom = new JPanel();
        bottom.setLayout(new BoxLayout(bottom, BoxLayout.Y_AXIS));

        final JSplitPane rightSplit = new JSplitPane(JSplitPane.VERTICAL_SPLIT);

        JPanel topContent = new MyScrollable(200);
        JPanel topFixed = new ShrinkGrow(topContent, rightSplit);
        topFixed.setLayout(new BoxLayout(topFixed, BoxLayout.X_AXIS));

        JScrollPane topFlexible = new JScrollPane(topContent);
        topFlexible.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED);
        topFlexible.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);

        JPanel bottomContent = new MyScrollable(300);
        JPanel bottomFixed = new ShrinkGrow(bottomContent, rightSplit);
        bottomFixed.setLayout(new BoxLayout(bottomFixed, BoxLayout.X_AXIS));

        JScrollPane bottomFlexible = new JScrollPane(bottomContent);
        bottomFlexible.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_AS_NEEDED);
        bottomFlexible.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);

        mainView.setBackground(Color.red);
        topFixed.setBackground(Color.green);
        topContent.setBackground(Color.green.darker());
        bottomFixed.setBackground(Color.blue);
        bottomContent.setBackground(Color.blue.darker());

        mainView.setMinimumSize(new Dimension(100, 100));
        mainView.setPreferredSize(new Dimension(400, 300));
        mainView.setMaximumSize(new Dimension(10000, 10000));

        topFixed.setMinimumSize(new Dimension(topFixed.getMinimumSize().width, 30));
        topFixed.setPreferredSize(new Dimension(topFixed.getPreferredSize().width, 30));
        topFixed.setMaximumSize(new Dimension(topFixed.getMaximumSize().width, 30));

        bottomFixed.setMinimumSize(new Dimension(bottomFixed.getMinimumSize().width, 40));
        bottomFixed.setPreferredSize(new Dimension(bottomFixed.getPreferredSize().width, 40));
        bottomFixed.setMaximumSize(new Dimension(bottomFixed.getMaximumSize().width, 40));

        topContent.setPreferredSize(new Dimension(100, 500));
        bottomContent.setPreferredSize(new Dimension(100, 400));

        top.add(topFixed);
        top.add(topFlexible);
        bottom.add(bottomFixed);
        bottom.add(bottomFlexible);
        rightSplit.setLeftComponent(top);
        rightSplit.setRightComponent(bottom);

        rightSplit.setMinimumSize(new Dimension(0, 0));

        final JSplitPane mainSplit = new MySplitPane(JSplitPane.HORIZONTAL_SPLIT, mainView, rightSplit);

        window.add(mainSplit);
        window.pack();
        window.setVisible(true);
    }
}

Answer 1

Add a MouseListener to the JSplitPane Divider to detect when the divider is being dragged. When dragged, respond to the property change events. Sample:

https://community.oracle.com/thread/1352161?start=0&tstart=0

SplitPaneUI spui = splitPane.getUI();
    if (spui instanceof BasicSplitPaneUI) {
      // Setting a mouse listener directly on split pane does not work, because no events are being received.
      ((BasicSplitPaneUI) spui).getDivider().addMouseListener(new MouseAdapter() {
        public void mouseClicked(MouseEvent e) {

Answer 2

...unless the divider is dragged far enough right in which case the right most component will have zero width.

To re-display the right component the user can then drag the divider far enough to the left.

sounds like all you have to do is disable the splitPane to disable dragging,

then setOneTouchExpandable() to true. you may need to remove one of the 'expandable'

buttons to disable expanding the wrong way

Answer 3

Not sure if possible to catch dragging event, but for sure you can catch propertyChange event. Catching events after you move a JSplitPane‘s divider can be made possible through the PropertyChangeListener JSplitPane class. Make sure you supply the DIVIDER_LOCATION_PROPERTY as the parameter so that this listener will listent to modified divider location events. If you do not supply this as the first parameter in the addPropertyChangeListener() method, you can always place a conditional statement if the PropertyChangeEvent‘s getPropertyName() method returns dividerLocation as the value.

jSplitPane1.addPropertyChangeListener(JSplitPane.DIVIDER_LOCATION_PROPERTY, new PropertyChangeListener() {
@Override
public void propertyChange(PropertyChangeEvent pce) {
    // do here
}
});