Handling Mouse Events
Event-Driven Programming
Approccio standard per programmare GUI
In contrapposizione al polling offre:
-
Maggiore flessibilità
Minor spreco di risorse
In Java 
Handling Mouse Events
Un oggetto può essere notificato dell’occorrenza di un evento registrandosi
come event listener implementando l’apposita interfaccia.
Ogni Swing Component è un event source e può avere più EventListener in
ascolto
L’occorrenza di un evento chiama la rispettivo metodo dell’EventListener.
(es. mouse clicked  MouseListener.mouseClicked() )
User clicks a button, presses Return
while typing in a text field, or chooses
a menu item
ActionListener
User closes a frame (main window)
WindowListener
User presses a mouse button while
the cursor is over a component
MouseListener
User moves the mouse over a
component
MouseMotionListener
Component becomes visible
ComponentListener
Table or list selection changes
ListSelectionListener
Handling Mouse Events
MouseEvents
(il puntatore entra o esce da un componente,
l’utente preme un bottone)
MouseListener
(Eventi che richiedono il tracciamento del
movimento del cursore)
MouseMotionListener
(MouseWheelEvents  MouseWheelListener)
Handling Mouse Events
MouseListener Interface
Method
Purpose
mouseClicked(MouseEvent)
Called just after the user clicks the listened-to component.
mouseEntered(MouseEvent)
Called just after the cursor enters the bounds of the listened-to component.
mouseExited(MouseEvent)
Called just after the cursor exits the bounds of the listened-to component.
mousePressed(MouseEvent)
Called just after the user presses a mouse button while the cursor is over the listened-to
component.
mouseReleased(MouseEvent)
Called just after the user releases a mouse button after a mouse press over the listened-to
component.
MouseMotionListener Interface
Method
Purpose
mouseDragged(MouseEvent)
Called in response to the user moving the mouse while holding a mouse button down. This
event is fired by the component that fired the most recent mouse-pressed event, even
if the cursor is no longer over that component.
mouseMoved(MouseEvent)
Called in response to the user moving the mouse with no mouse buttons pressed. This event
is fired by the component that's currently under the cursor.
Handling Mouse Events
MouseEvent Class
Method
Purpose
int getClickCount()
Return the number of quick, consecutive clicks the user has made (including this event). For
example, returns 2 for a double click.
int getX()
int getY()
Point getPoint()
Return the (x,y) position at which the event occurred, relative to the component that fired the
event.
int getButton()
Return which mouse button, if any, has changed state. One of the following constants is
returned: NOBUTTON, BUTTON1, BUTTON2, or BUTTON3. Introduced in release 1.4.
boolean isPopupTrigger()
Return true if the mouse event should cause a popup menu to appear. Because popup triggers
are platform dependent, if your program uses popup menus, you should call
isPopupTrigger for all mouse-pressed and mouse-released events fired by components
over which the popup can appear. See Bringing Up a Popup Menu for more information
about popup menus.
String getMouseModifiersText(int)
Return a String describing the modifier keys and mouse buttons that were active during the
event, such as "Shift", or "Ctrl+Shift". These strings can be localized using the
awt.properties file. Introduced in release 1.4.
Handling Mouse Events
Implementando le Interfacce MouseListener e
MouseMotionListener si è costretti ad implementare tutti
i metodi
Spesso ci interessano solo alcuni eventi (pochi metodi)
Classi Adapter
(estendono le interfacce e danno una imlementazione di default dei
metodi)
MouseAdapter mplements MouseListener
MouseMotionAdapter implements MouseMotionListener
MouseInputadapter implements MouseInputListener and MouseMotionListener
Handling Mouse Events
Esempio: MouseXY
Handling Mouse Events
Esempio: MouseXY
class MouseXY extends Frame implements WindowListener, MouseListener
{
public MouseXY(String text) {
super(text);
addWindowListener(this);
addMouseListener(this);
}
public void mouseClicked(MouseEvent event) {}
public void mouseEntered(MouseEvent event) {}
public void mouseExited(MouseEvent event) {}
public void mouseReleased(MouseEvent event) {}
…….
Handling Mouse Events
Esempio: MouseXY
public void mousePressed(MouseEvent event) {
int xCoord = event.getX();
int yCoord = event.getY();
Graphics g = getGraphics();
g.drawString("+ [" + String.valueOf(xCoord) + "," +
String.valueOf(yCoord) + "]",
xCoord,yCoord);
}
Handling Mouse Events
Esempio: MouseXY
public void
public void
public void
public void
public void
public void
public void
windowClosed(WindowEvent event) {}
windowDeiconified(WindowEvent event) {}
windowIconified(WindowEvent event) {}
windowActivated(WindowEvent event) {}
windowDeactivated(WindowEvent event) {}
windowOpened(WindowEvent event) {}
windowClosing(WindowEvent event) { System.exit(0); }
public static void main(String[] args) {
MouseXY screen = new MouseXY("Mouse example");
screen.setSize(400,300);
screen.setVisible(true);
}
}
Handling Mouse Events
Esempio: MousePainter
Handling Mouse Events
Esempio: MousePainter
public class MousePainter extends JFrame{
private int xValue = -10, yValue = -10;
boolean rubber = false;
Label label;
Button toolButton;
public MousePainter () {
super("Mouse Painter Example");
label = new Label("Drag mouse to paint");
toolButton = new Button("Use Rubber");
toolButton.addMouseListener(
new MouseInputAdapter () {
public void mouseClicked(MouseEvent e){
if (e.getButton() == 1) {
String newLabel = rubber ?
"Use rubber" :
"Use pen";
toolButton.setLabel(newLabel);
rubber = rubber ? false : true;
}
}
}
);
Handling Mouse Events
Esempio: MousePainter
getContentPane().add(toolButton,BorderLayout.NORTH);
getContentPane().add(label,BorderLayout.SOUTH);
setSize(350,350);
addMouseMotionListener (
new MouseMotionAdapter () {
public void mouseDragged(MouseEvent e){
xValue = e.getX();
yValue = e.getY();
repaint();
}
}
);
show();
};
Handling Mouse Events
Esempio: MousePainter
public void paint(Graphics g) {
if (rubber) {
g.clearRect(xValue,yValue,15,15);
} else {
g.fillOval(xValue,yValue,3,3);
};
};
public static void main(String[] args){
MousePainter app = new MousePainter();
app.addWindowListener(
new WindowAdapter() {
public void windowClosing(WindowEvent e){
System.exit(0);
}
}
);
}
}
Handling Mouse Events
Esempio: MousePainter
addMouseListener (
new MouseInputAdapter () {
public void mouseDragged(MouseEvent e){
xValue = e.getX();
yValue = e.getY();
repaint();
}
public void mouseClicked(MouseEvent e){
if (e.getComponent().equals(toolButton)) {
String newLabel = rubber ? "Use rubber" : "Use pen";
toolButton.setLabel(newLabel);
rubber = rubber ? false : true;
}
}
}
);