Swing Tip: JSplitPane with zero-size divider

Modern GUIs are becoming more and more minimalistic. Most controls (e.g. text fields or buttons) nowadays use 1 pixel thin borders. Everybody is removing borders from scroll and split panes. Even the split pane divider is often reduced to 1 pixel (e.g. on Mac OS X since years or in current Mozilla Thunderbird).

But how to create a 1 pixel thin divider with JSplitPane?

First idea was of course to invoke splitPane.setDividerSize(1). This seems to work, but has the disadvantage that it is very hard for the user to hit that single pixel line to move the divider. What we need is a transparent divider that has a easy-to-hit width (e.g. 9 pixels) and is placed between and over the left and right split pane components.

zeros-size split divider

Thanks to Swing's flexible design, it is relative easy to implement this.

First we set the divider size to 1 and let the split pane layout manager do its work. The trick is now to override JSplitPane.layout() and modify the bounds of the divider (e.g. increase width and move left):

public class JSplitPaneWithZeroSizeDivider extends JSplitPane {
    private int dividerDragSize = 9;
    private int dividerDragOffset = 4;

    public JSplitPaneWithZeroSizeDivider() {
        setDividerSize( 1 );
        setContinuousLayout( true );
    }

    @Override
    public void layout() {
        super.layout();

        // increase divider width or height
        BasicSplitPaneDivider divider = ((BasicSplitPaneUI)getUI()).getDivider();
        Rectangle bounds = divider.getBounds();
        if( orientation == HORIZONTAL_SPLIT ) {
            bounds.x -= dividerDragOffset;
            bounds.width = dividerDragSize;
        } else {
            bounds.y -= dividerDragOffset;
            bounds.height = dividerDragSize;
        }
        divider.setBounds( bounds );
    }

Then we need our own UI delegate that creates our divider.

    @Override
    public void updateUI() {
        setUI( new SplitPaneWithZeroSizeDividerUI() );
        revalidate();
    }

    private class SplitPaneWithZeroSizeDividerUI extends BasicSplitPaneUI {
        @Override
        public BasicSplitPaneDivider createDefaultDivider() {
            return new ZeroSizeDivider( this );
        }
    }

And finally our divider, which draws the divider line and updates the drag locations.

    private class ZeroSizeDivider extends BasicSplitPaneDivider {
        public ZeroSizeDivider( BasicSplitPaneUI ui ) {
            super( ui );
            super.setBorder( null );
            setBackground( UIManager.getColor( "controlShadow" ) );
        }

        @Override
        public void setBorder( Border border ) {
            // ignore
        }

        @Override
        public void paint( Graphics g ) {
            g.setColor( getBackground() );
            if( orientation == HORIZONTAL_SPLIT )
                g.drawLine( dividerDragOffset, 0, dividerDragOffset, getHeight() - 1 );
            else
                g.drawLine( 0, dividerDragOffset, getWidth() - 1, dividerDragOffset );
        }

        @Override
        protected void dragDividerTo( int location ) {
            super.dragDividerTo( location + dividerDragOffset );
        }

        @Override
        protected void finishDraggingTo( int location ) {
            super.finishDraggingTo( location + dividerDragOffset );
        }
    }
}

That's it.

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Tested with Oracle/Sun Java 5, 6, and 7. Licensed under BSD-2-Clause with clause 2 removed.

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JFormDesigner 5.0.1 and 5.1 Beta 3

We've just released JFormDesigner 5.0.1 and 5.1 Beta 3.

JFormDesigner 5.0.1

This release fixes minor bugs and brings some minor improvements.

If you're running JFormDesigner in a Java 7 VM, it is recommened to update to this release because it fixes a NullPointerException when using TitledBorder and running JFormDesigner in a Java 7 VM.

See Change Log for details and download JFormDesigner 5.0.1.

JFormDesigner 5.1 Beta 3

Beta 3 Change Log:

  • Go to event handler method in Java editor.
  • All fixes from JFormDesigner 5.0.1.

Beta 2 Change Log:

  • NetBeans: Project specific options.
  • Palette: Display multiple items per row if there is enough room.
  • Palette: New option "Item Names" in context menu to show only item icons.
  • NetBeans: fixed too dark background of panels, palette, headers, etc on Mac.
  • NetBeans: bug fixes.
  • Fixed NullPointerException when using TitledBorder and running
    JFormDesigner in a Java 7 VM.

Please give it a try, download it and report bugs. Thanks.

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JFormDesigner 5.1 Beta; NetBeans plug-in

Finally, the first build of the JFormDesigner plug-in for NetBeans is available now as part of JFormDesigner 5.1 Beta.

NetBeans plug-in

Major new features and improvements:

  • NetBeans plug-in.
  • JGoodies Forms 1.4 support.
  • New JFDML persistence format for .jfd form files. This is a compact, easy-to-merge and fast-to-load format.

Please have a look at the change log for a complete list of changes.

Please give it a try, download it and report bugs. Thanks.

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