Swing Hacks

Add a Filter History #14

Chapter 2, Lists and Combos

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63

HACK

H A C K

#14

Add a Filter History

Hack #14

Remember previous searches and research with one click.

Chances are good that if you’ve searched for something once, it’s important

enough that you might well search for it again. In Apple’s Safari browser, a

search widget at the upper right has a little magnifying glass that remembers

your last 10 searches. Click the magnifying glass and a pop up appears with

the previous searches. Select one and it populates the field and does the

search immediately.

Here’s an implementation of the same idea, grafted onto the previous hack.

In other words, this remembers previous filters. It doesn’t remember every

keystroke—why bother remembering the searches “J” and “Jo” when you’re

really just interested in “Joe”—and only adds a search term to the filter

when the user presses return.

In the previous hack, you just needed to have a text field and a

JList. Now a

JButton needs to be attached to the text field, so the two are bundled

together in the inner class

FilterField. This class is responsible for:

• Telling the model to refilter on each keystroke in the

JTextField, as

before.

• Remembering the

JTextField’s contents as a saved search anytime the

Return or Enter key is pressed.

• Catching clicks on the

JButton and popping up a menu with previous

searches.

• Populating the

JTextField with a previous search when one is selected

from the list. It doesn’t need to explicitly tell the model to refilter

because changing the text area will fire a

DocumentEvent that is already

accounted for by the

JTextField’s DocumentListener.

Example 2-5 shows the new

FilterField class.

Example 2-5. List filtering component with text field and history button

class FilterField extends JComponent

implements DocumentListener, ActionListener {

LinkedList prevSearches;

JTextField textField;

JButton prevSearchButton;

JPopupMenu prevSearchMenu;

public FilterField (int width) {

super( );

setLayout(new BorderLayout( ));

textField = new JTextField (width);

textField.getDocument( ).addDocumentListener (this);

textField.addActionListener (this);

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Chapter 2, Lists and Combos

#14 Add a Filter History

HACK

Notice how this version of the class uses a MouseListener on the JButton

instead of an ActionListener. Either will work, but the MouseEvent provides

the location of the mouse click as a

Point in the JButton’s coordinate space,

which is useful for showing the pop-up menu at the exact point of the

mouse click. There is an

ActionListener implementation, but it’s for the

JTextField so that when the user presses the Return key, the filter text is

saved to the

JPopupMenu (and, if there are more than 10 items, the oldest

saved search is removed).

prevSearchButton =

new JButton (new ImageIcon ("mag-glass.png"));

prevSearchButton.setBorder(null);

prevSearchButton.addMouseListener (new MouseAdapter( ) {

public void mousePressed (MouseEvent me) {

popMenu (me.getX(), me.getY( ));

}

});

add (prevSearchButton, BorderLayout.WEST);

add (textField, BorderLayout.CENTER);

prevSearches = new LinkedList ( );

}

public void popMenu (int x, int y) {

prevSearchMenu = new JPopupMenu( );

Iterator it = prevSearches.iterator( );

while (it.hasNext( ))

prevSearchMenu.add (

new PrevSearchAction(it.next().toString( )));

prevSearchMenu.show (prevSearchButton, x, y);

}

public void actionPerformed (ActionEvent e) {

// called on return/enter, adds term to prevSearches

if (e.getSource( ) == textField) {

prevSearches.addFirst (textField.getText( ));

if (prevSearches.size( ) > 10)

prevSearches.removeLast( );

}

}

public void changedUpdate (DocumentEvent e) {

((FilterModel)getModel()).refilter( );

}

public void insertUpdate (DocumentEvent e) {

((FilterModel)getModel()).refilter( );

}

public void removeUpdate (DocumentEvent e) {

((FilterModel)getModel()).refilter( );

}

}

Example 2-5. List filtering component with text field and history button (continued)

Add a Filter History #14

Chapter 2, Lists and Combos

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65

HACK

The items in the JPopupMenu are instances of PrevSearchAction, which sub-

classes Swing’s

Action. This is convenient because they provide a String rep-

resentation to be shown in the pop-up menu, yet get an

actionPerformed( )

when their menu item is selected, which gives them a chance to reset the fil-

ter text. Here’s what the

PrevSearchAction

inner class looks like:

class PrevSearchAction extends AbstractAction {

String term;

public PrevSearchAction (String s) {

term = s;

putValue (Action.NAME, term);

}

public String toString( ) { return term; }

public void actionPerformed (ActionEvent e) {

getFilterField( ).textField.setText (term);

}

}

When a previous search is recalled, it looks like Figure 2-4.

And when the mouse clicks on one of the menu items, the field is populated

and the list is filtered. Figure 2-5 shows the result.

Figure 2-4. Pop-up menu with previous searches

Figure 2-5. List filtered by pop-up selection