Swing Hacks

Spin Open a Detail Pane #39

Chapter 5, Windows, Dialogs, and Frames

|

203

HACK

The Invisible Man

This hack is fairly simple and relies on one fact: you can add a component to

a layout and alternately make it visible and invisible. Its position relative to

other components is preserved when it’s invisible, but it takes up no

onscreen space. So, a spin-open container consists of three components:

• The top component, which is always visible

• The spinner

• The bottom component, whose visibility can be set by clicking on the

spinner

The layout of these three is pretty straightforward, as seen in Example 5-6,

which lists the

MoreInfoPanel class but omits an inner class (for now).

Example 5-6. Laying out the three panel components

public class MoreInfoPanel extends JPanel {

public Component topComponent;

protected SpinWidget spinWidget;

public Component bottomComponent;

public static final int SPIN_WIDGET_HEIGHT = 14;

public MoreInfoPanel (Component tc, Component mic) {

topComponent = tc;

spinWidget = new SpinWidget( );

bottomComponent = mic;

doMyLayout( );

}

protected void doMyLayout( ) {

setLayout (new BoxLayout (this, BoxLayout.Y_AXIS));

add (topComponent);

add (spinWidget);

add (bottomComponent);

resetBottomVisibility( );

}

protected void resetBottomVisibility( ) {

if ((bottomComponent == null) ||

(spinWidget == null))

return;

bottomComponent.setVisible (spinWidget.isOpen( ));

revalidate( );

if (isShowing( )) {

Container ancestor = getTopLevelAncestor( );

if ((ancestor != null) && (ancestor instanceof Window))

((Window) ancestor).pack( );

204

|

Chapter 5, Windows, Dialogs, and Frames

#39 Spin Open a Detail Pane

HACK

The constructor simply assigns the top and bottom Components to local vari-

ables, creates a

SpinWidget (see Example 5-7), and calls doMyLayout( ). The

latter method puts the components into a vertical

BoxLayout and calls the

convenience method

resetBottomVisibility( ).

resetBottomVisibility( ) is responsible for setting the visibility of the bot-

tom component based on whether the

SpinWidget is currently open or

closed. It then finds and re-

pack( )s its parent Window, so that if the bottom

component is wider than the top, the enclosing window will resize to fit the

now-visible contents. Of course, this behavior might not be appropriate in

some cases: you might put a

MoreInfoPanel in a complex GUI and not want

to re-

pack( ) the parent Window. Imagine an IDE in which you browse items

in a list or tree on the left, and show varying levels of detail on the right with

nested

MoreInfoPanels. The right pane might want to get sizing-related

events when its child

MoreInfoPanels change sizes, but it wouldn’t be appro-

priate for them to try to resize the entire

JFrame. This might call for hacking

the hack to set up an event-listener system, so that you could deliver sizing-

related events to a specific parent.

Now for the

SpinWidget, shown in Example 5-7. I wrote this as a custom

JPanel that draws the triangles with graphics primitives. This has the advan-

tage of being self-contained, but if you’d rather just use a

JButton with hand-

drawn triangle GIFs, go for it.

repaint( );

}

}

public void showBottom (boolean b) {

spinWidget.setOpen (b);

}

public boolean isBottomShowing ( ) {

return spinWidget.isOpen( );

}

// See below for SpinWidget inner class

}

Example 5-7. Inner class spin triangle

public class SpinWidget extends JPanel {

boolean open;

Dimension mySize = new Dimension (SPIN_WIDGET_HEIGHT,

SPIN_WIDGET_HEIGHT);

final int HALF_HEIGHT = SPIN_WIDGET_HEIGHT / 2;

int[] openXPoints =

{ 1, HALF_HEIGHT, SPIN_WIDGET_HEIGHT-1};

Example 5-6. Laying out the three panel components (continued)

Spin Open a Detail Pane #39

Chapter 5, Windows, Dialogs, and Frames

|

205

HACK

As you can see, the code does some work to create the points for the two tri-

angle polygons, which are used in the

paint( ) method. Other than that, it’s

a simple state machine with two

boolean states: when it gets a click, it

switches states. The call to

setOpen( ) calls the enclosing class’s

resetButtonVisibility( ), which will make the bottom component visible.

int[] openYPoints =

{ HALF_HEIGHT, SPIN_WIDGET_HEIGHT-1, HALF_HEIGHT};

int[] closedXPoints =

{ 1, 1, HALF_HEIGHT};

int[] closedYPoints =

{ 1, SPIN_WIDGET_HEIGHT-1, HALF_HEIGHT };

Polygon openTriangle =

new Polygon (openXPoints, openYPoints, 3);

Polygon closedTriangle =

new Polygon (closedXPoints, closedYPoints, 3);

public SpinWidget( ) {

setOpen (false);

addMouseListener (new MouseAdapter( ) {

public void mouseClicked (MouseEvent e) {

handleClick( );

}

});

}

public void handleClick( ) {

setOpen (! isOpen( ));

}

public boolean isOpen( ) {

return open;

}

public void setOpen (boolean o) {

open = o;

resetBottomVisibility( );

}

public Dimension getMinimumSize( ) { return mySize; }

public Dimension getPreferredSize( ) { return mySize; }

// don't override update( ), get the default clear

public void paint (Graphics g) {

if (isOpen( ))

g.fillPolygon (openTriangle);

else

g.fillPolygon (closedTriangle);

}

}

Example 5-7. Inner class spin triangle (continued)