Swing Hacks

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Chapter 2, Lists and Combos

#20 Create a Collections-Aware JComboBox

HACK

The MapComboBoxModel accepts a collection in its constructor—this time a

Map—saving it for later reference. To maintain the order of the keys, the class

uses a

List called index. The constructor calls buildIndex( ) to populate the

List with the Map’s set of keys, and then sets the selected item—just like in

the

List version. getElementAt( ) uses the index to get the display values and

getSize( ) uses the size of the Map itself.

actionPerformed( ) is different from the List version and calls buildIndex( )

before fireUpdate( ). This ensures that the index is always in sync with the

underlying map and that the

JComboBox reflects that. There is no implemen-

tation of

fireUpdate( ) or managing the listeners because the parent class,

ListComboBoxModel, takes care of those.

index = new ArrayList( );

buildIndex( );

if(index.size( ) > 0) {

selected = index.get(0);

}

}

protected void buildIndex( ) {

index = new ArrayList(map_data.keySet( ));

}

public Object getElementAt(int i) {

return index.get(i);

}

public int getSize( ) {

return map_data.size( );

}

public void actionPerformed(ActionEvent evt) {

if(evt.getActionCommand( ).equals("update")) {

buildIndex( );

fireUpdate( );

}

}

public Object getValue(Object selectedItem) {

return map_data.get(selectedItem);

}

public Object getValue(int selectedItem) {

return getValue(index.get(selectedItem)); ...