Swing Hacks

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Chapter 8, Rendering

#58 Block a Window Without a Modal Dialog

HACK

// create the right-click glass pane.

Component rc = new RightClickGlassPane(frame.getContentPane( ),popup);

// set as glasspane and make it visible

frame.setGlassPane(rc);

rc.setVisible(true);

// pack and show the frame

frame.pack( );

frame.setSize(400,200);

frame.show( );

}

While most of this is boilerplate, be sure to notice the call to rc.setVisible().

This is where the glass pane is turned on. If the glass pane is not visible, then

your code won’t ever receive events and work its magic.

This hack only demonstrates intercepting a mouse click, but it could be used

for any other type of event capturing, such as remapping one key to another,

recording mouse events, blocking mouse events

[Hack #58], or creating com-

pletely synthetic events to fool the program.

H A C K

#58

Block a Window Without a Modal Dialog Hack #58

Block the input in a single window during long operations without stopping

your entire application.

Since the dawn of GUIs, most toolkits have had the concept of a modal dia-

log box. This is a small window that restricts input to itself, blocking access

to the rest of the program (or entire operating system in some cases). Modal

windows often produce the desired effect, but sometimes you need a win-

dow that can block itself without blocking access to the whole application.

The most common use for such a window is a long running process, like ren-

dering frames of a movie or waiting for the network to respond. In this case,

you would like to let the user still interact with the rest of the application but

block the one window that represents the work in progress. Swing doesn’t

provide a modal window like this, but since when has that stopped us?

Blocking Basics

To block a window, you could disable the components within it, but then

you would need to recursively find each component and disable it manu-

ally. This is a big headache, and would make for a very ugly window (all

those grayed-out components). All you really want to do is capture all input

to the window and block that. Swing provides a great way to do this: the

glass pane. The glass pane sits on top of all other components in a window,

making it the perfect place to implement blocking behavior.

Block a Window Without a Modal Dialog #58

Chapter 8, Rendering

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297

HACK

Since you want your glass pane to be transparent, it’s best to start with a

plain

JComponent that doesn’t draw anything. Example 8-3 defines a

WindowBlocker

class that extends

JComponent

and implements the

MouseInputListener

(a compound interface that combines the

MouseListener

and

MouseMotionListener

).

So far, the code is pretty simple. The

WindowBlocker catches all mouse events

and does nothing, sending the events to that great bit bucket in the sky.

When the user presses the mouse, the computer will beep, indicating that

the window is busy. The component still won’t actually receive events

because it is invisible by default. When you are ready to start blocking

events, you should make the component visible. That’s where the

block( )

method comes in:

private Cursor old_cursor;

public void block( ) {

old_cursor = getCursor( );

setCursor(Cursor.getPredefinedCursor(Cursor.WAIT_CURSOR));

setVisible(true);

}

public void unBlock( ) {

setCursor(old_cursor);

setVisible(false);

}

Example 8-3. Listening for mouse events

public class WindowBlocker extends JComponent

implements MouseInputListener {

public WindowBlocker( ) {

addMouseListener(this);

addMouseMotionListener(this);

}

public void mouseMoved(MouseEvent e) {

}

public void mouseDragged(MouseEvent e) {

}

public void mouseClicked(MouseEvent e) {

}

public void mouseEntered(MouseEvent e) {

}

public void mouseExited(MouseEvent e) {

}

public void mousePressed(MouseEvent e) {

Toolkit.getDefaultToolkit().beep( );

}

public void mouseReleased(MouseEvent e) {

}