Swing Hacks

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Chapter 1, Basic JComponents

#10 Building a Drop-Down Menu Button

HACK

With the code so far, you can show the pop-up window. To close it, you

must listen for ancestor events to find out when something above the drop-

down in the component tree has changed. They all just call

hidePopup( )

to

safely turn it off:

public void ancestorAdded(AncestorEvent event){

hidePopup( );

}

public void ancestorRemoved(AncestorEvent event){

hidePopup( );

}

public void ancestorMoved(AncestorEvent event){

if (event.getSource( ) != popup) {

hidePopup( );

}

}

public void hidePopup( ) {

if(popup != null && popup.isVisible( )) {

popup.setVisible(false);

}

}

Adding a Color Selection Panel

With the DropDownComponent finished, you can finally build something with

it. For this hack, I’ve chosen a color selector. This is a small widget that lets

the user pick one of 12 standard colors without having to open up a full

color chooser. Most word processors and spreadsheets have a component

like this, so there’s no reason for Swing not to have one, too.

ColorSelectionPanel, shown in Example 1-22, is just a JPanel with a 4 × 3

grid of buttons. Each button represents one of the most common 10 colors,

plus black and white. When a color button is clicked, it will call

selectColor( ) to fire off a color selection event.

Example 1-22. A color selection panel to be used in the drop-down component

public class ColorSelectionPanel extends JPanel ...