Downloaded 16 times
![Example
• Create a listener object and register it with the button:
class BeeperFrame extends JFrame
{ public BeeperFrame()
{ …
button = new JButton("Click Me");
button.addActionListener(new
ClickListener());
}
}
• The driver class:
public class Beeper
{ public static void main(String[] args)
{ BeeperFrame frame = new BeeperFrame();
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.show();
}
} //Check out Beeper1.java (inner class)](https://image.slidesharecdn.com/09events-160928113037/85/09events-10-320.jpg)
More Related Content
09events
- 1. Topic 9: EventHandling Reading: Chapter 8 Advanced Programming Techniques
- 2. Objective and Outline •Objective: – Show how to write GUI programs that react to user actions. • Outline: – Java AWT event delegation model • An example – The AWT event hierarchy – Individual events • KeyEvents • MouseEvents – Special classes and interfaces for event handling • Adapter classes • The Action interface
- 3. Java AWT eventdelegation model Java automatically generates event objects when Mouse or button clicked Menu, checkbox, or text selected Keyboard typed Scrollbar adjusted ….. It is up to the programmer to decide whether to do anything or what to do when an event happens
- 4. • Event source: –An object that generates events • Listener: – Receives events and decides what to do Java AWT event delegation model Event Listener Event Source Event Object evt
- 5. Java AWT eventdelegation model • Notes – A listener must be registered with an event source in order to listen for events produced there. • An event source can have multiple listeners and vice versa – A listener class must implement a listener interface, which decides the response to an event.
- 6. Java AWT eventdelegation model Any objects of class that implements an appropriate listener interface class Listener implements ActionListener { … actionPerformed(Event evt) {…} } Has to register its own listeners Source.addActionL istener(Listener) Event Listener Event Source Event Object evt
- 7. Java AWT eventdelegation model • The event handling process: – When an event occurs, event source sends event objects to all registered listeners. – Listeners use information encapsulated in the event objects to determine what to do. Event Listener Event Source Event Object evt
- 8. Example • A buttonthat beeps when clicked (Beeper.java) – Create a GUI with one button class BeeperFrame extends JFrame { public BeeperFrame() { setSize( 300, 200); button = new JButton("Click Me"); getContentPane().add(button, BorderLayout.CENTER); } private JButton button; } Javax.swing.JButton has five constructors Java.awt.Container void add(Component) Adding button directly onto contentPane. Bad programming style.
- 9. Example • When abutton is clicked, an ActionEvent object is produced (java.awt.event.ActionEvent). • Listener for an ActionEvent: an object of a class that implements the ActionListener Interface • class ClickListener implements ActionListener { public void actionPerformed(ActionEvent e) { Toolkit.getDefaultToolkit().beep(); } }
- 10. Example • Create alistener object and register it with the button: class BeeperFrame extends JFrame { public BeeperFrame() { … button = new JButton("Click Me"); button.addActionListener(new ClickListener()); } } • The driver class: public class Beeper { public static void main(String[] args) { BeeperFrame frame = new BeeperFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.show(); } } //Check out Beeper1.java (inner class)
- 11. Outline • Outline: – JavaAWT event delegation model • Two examples – The AWT event hierarchy – Individual events • KeyEvents • MouseEvents – Special classes and interfaces for event handling • Adapter classes • The Action interface
- 12. The AWT EventHierarchy EventObject AWTEvent Component Event Item Event Action Event Adjustment Event Text Event Input Event Paint Event Container Event Focus Event Window Event Key Event Mouse Event java.util java.awt.event Programmer no need to worry about paint events ……. Swing has more event types Programmer can create new event types
- 13. 11 listener interfacesin java.awt.event ActionListener KeyListener AdjustmentListener MouseListener ComponentListener MouseMotionListener ContainerListener TextListener FocusListener WindowListener ItemListener The AWT Event Hierarchy
- 14. Semantic Events: Whatuser does ActionEvent (button click, menu selection) AdjustmentEvent (adjusting scroll bar) ItemEvent (selection from checkbox or list items) TextEvent (the contents of a text field or text area were changed) Additional events (like MenuEvent, ChangeEvent) can be found in javax.swing.event. They are associated with Swing components and easy to handle. Will discuss some in the next topic. The AWT Event Hierarchy
- 15. Low-Level Events: facilitatesemantic events ComponentEvent (component resized, moved, shown, or hidden) (A component is a user interface elements such as button, text field, scrollbar, panel, frame) ComponentEvent is the ancestor of all low-level event classes FocusEvent (component get focus) ContainerEvent (a component has been added or removed. Programmers no need to worry about it) (A container is a screen area or component that can contain components. E.g. window, panel) The AWT Event Hierarchy
- 16. Low-Level Events: facilitatessemantic events KeyEvent (key pressed or released) MouseEvent (mouse button pressed, released, moved, or dragged) WindowEvent (window activated, deactivated, iconified, deiconified, or closed) Will discuss KeyEvent and MouseEvent The AWT Event Hierarchy
- 17. Last Time • AWTevent delegation model – Event source: • What are inside an event class? • How to find out the types of events that a component generates? – Listener: • What are inside an listener class?
- 18. Creating a ResponsiveGUI • Set up GUI – Layout various components on the contenPane of top-level container • Decide which events to handle – Begin with design objectives: Functionalities of GUI – For each component, find out the events that it generates • Check API of component class and look for methods addXXXXListener – implies that the component produces events of type XXXEvent • Handle events – Write listener class • Check API of listener interface and decide which methods to override • Check API of event class so as to get information about events – Create listener object – Register listener object with event source
- 19. Objective and Outline •Objective: – Show how to write GUI programs that react to user actions. • Outline: – Java AWT event delegation model • An example – The AWT event hierarchy – Individual events • KeyEvents • MouseEvents – Special classes and interfaces for event handling • Adapter classes • The Action interface
- 20. • Focus – AGUI consists of many components. – Which component received keystrokes? • The component that has focus • Focus is gained or lost in response to user actions: – A component gains focus if the user clicks the mouse inside it. – Or TAB/SHIT-TAB key can be used to traverses components which can receive input focus KeyEvent
- 21. • Methods ofjava.awt.Component for managing focus – void requestFocus(): Moves focus to this component – boolean isFocusable(): Tells whether a component can be reached by using TAB or SHIFT- TAB – void transferFocus(): Transfer focus to the next component in the traversal order. KeyEvent
- 22. KeyEvent FocusEvent is generatedwhen a component gains focus or loses focus. Refer to textbook for how to handle focus events.
- 23. Java distinguishes betweencharacters and virtual key code – “A” and “a” have the same code VK_A – There is no VK_a !! – More examples: VK_COMMA, VK_PERIOD, VK_OPEN_BRACKET, VK_SHIFT ... KeyEvent
- 24. • KeyEvent objectsare generated by the component with focus when a key is pressed or released. – Typing “a” generates three KeyEvent objects • 2 Lower-level events – keyPressed VK_A (Virtual key code) – keyReleased VK_A (Virtual key code) • One higher-level event: keyTyped “a” – Only for keys that generate character input • Methods of java.awt.event.KeyEvent Class: – getKeyCode() to get back virtual key code. – getKeyChar() to get back the key character – …. KeyEvent
- 25. Methods in theKeyListener Interface: keyPressed(KeyEvent e) (what to do when VK_A pressed?) keyReleased(KeyEvent e) (what to do when VK_A released?) keyTyped(KeyEvent e) (what to do when “a” is typed?) e.getKeyCode() seems to give 0 within keyTyped Will illustrate with example KeyEvent
- 26. Example: Sketch.java Move witheither cursor keys or “h”, “j”, “k”, “l” keys Move faster when SHIFT is pressed KeyEvent
- 27. Setup: public SketchPanel extendsJPanel { public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; // draw all lines for (int i = 0; i < lines.size(); i++) g2.draw((Line2D)lines.get(i)); } public void add(int dx, int dy) .. // add line segement last (x, y) –-- (x+dx, y+dy) // calls repaint() private ArrayList lines private Point2D last; // last point KeyEvent
- 28. Getting focus andregister key listener public class SketchPanel { public SketchPanel() { … KeyHandler listener = new KeyHandler(); addKeyListener(listener); } public boolean isFocusable() { return true; } … } ..} KeyEvent We need this because by default a panel cannot get keyboard focus
- 29. Processing cursor keys: classKeyHandler implements KeyListener { public void keyPressed(KeyEvent event) { // set distance: whether shift is down int d; if (event.isShiftDown()) d = LARGE_INCREMENT; else d = SMALL_INCREMENT; // direction of move: what key is typed int keyCode = event.getKeyCode(); if (keyCode == KeyEvent.VK_LEFT) add(-d, 0); else if (keyCode == KeyEvent.VK_RIGHT) add(d, 0); else if (keyCode == KeyEvent.VK_UP) add(0, -d); else if (keyCode == KeyEvent.VK_DOWN) add(0, d); } KeyEvent Note: Can also use getModifiers of InputEvent or getKeyModifiers of KeyEvent to find out whether SHIFT is down
- 30. Typing keys “h”.“j”, “k”, “l”: public void keyTyped(KeyEvent event) { char keyChar = event.getKeyChar(); int d; // distance of move if (Character.isUpperCase(keyChar)) { d = LARGE_INCREMENT; keyChar = Character.toLowerCase(keyChar); } else d = SMALL_INCREMENT; // direction of move if (keyChar == 'h') add(-d, 0); else if (keyChar == 'l') add(d, 0); else if (keyChar == 'k') add(0, -d); else if (keyChar == 'j') add(0, d); } KeyEvent Note: Can also use getModifiers of InputEvent or getKeyModifiers of KeyEvent to find out whether upper case or lower case
- 31. Things to Try •Delete isFocusable() • getKeyCode within keyTyped • Modify example so that event source and listener are the same object • Make the listener class in Sketch.java an anonymous inner class.
- 32. Objective and Outline •Objective: – Show how to write GUI programs that react to user actions. • Outline: – Java AWT event delegation model • An example – The AWT event hierarchy – Individual events • KeyEvents • MouseEvents
- 33. MouseEvent • Just wantto know whether a button or menu is clicked? – No need to use mouse events explicitly. – Instead use ActionEvents generated by button or menu. • For drawing with mouse, mouse events are important.
- 34. • MouseEvent objectsgenerated by components where mouse cursor is located • Getting information about MouseEvents – int getX(), int getY() to get the x , y coordinates of mouse pointer. – Point getPoint() to get coordinates of mouse pointer as a Point object – int getClickCount() to get number of consecutive clicks. – int getModifiers() to find out, among other things, which mouse button is clicked. MouseEvent
- 35. • Two listenerinterfaces – MouseListener • mousePressed(MouseEvent evt) – Invoked when a mouse button has been pressed on a component. • mouseReleased(MouseEvent evt) – Invoked when a mouse button has been released on a component. • mouseClicked(MouseEvent evt) – Invoked when the mouse button has been clicked (pressed and released) on a component. • mouseEntered(MouseEvent e) Invoked when the mouse enters a component. • mouseExited(MouseEvent e) Invoked when the mouse exits a component. MouseEvent
- 36. • MouseMotionListener – mouseMoved(MouseEventevt) • API: Invoked when the mouse cursor has been moved onto a component but no buttons have been pushed. • Actual: invoked frequently while mouse is moving – mouseDragged(MouseEvent evt) • API: Invoked when a mouse button is pressed on a component and then dragged. • Actual: invoked frequently while mouse is being MouseEvent
- 37. MouseEvent MouseTest.java -- place,move, and erase squares Setup: class MousePanel extends JPanel { public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; // draw all squares for (int i = 0; i < squares.size(); i++) g2.draw((Rectangle2D)squares.get(i)); } private static final int SIDELENGTH = 10; private ArrayList squares; private Rectangle2D current; … }
- 38. MouseEvent MousePanel –Basic methods classMousePanel extends JPanel {… // Finds the first square containing a point. // Returns null when no square contains the point public Rectangle2D find(Point2D p){…} // Adds a square to collection public void add(Point2D p){…} // Removes a square to collection public void remove(Point2D p){…} …
- 39. MouseEvent MousePanel generates MouseEvents,which will be handled by MouseHandler and MouseMotionHandler class MousePanel extends JPanel { … public MousePanel() { squares = new ArrayList(); current = null; addMouseListener(new MouseHandler()); addMouseMotionListener( new MouseMotionHandler()); } … }
- 40. MouseEvent MouseHandler is aninner class of MousePanel class MousePanel extends Jpanel { private class MouseHandler implements MouseListener { public void mousePressed(MouseEvent event) { // add a new square if the cursor isn't inside a square current = find(event.getPoint()); if (current == null) add(event.getPoint()); } public void mouseClicked(MouseEvent event) { // remove the current square if double clicked current = find(event.getPoint()); if (current != null && event.getClickCount() >= 2) remove(current); …
- 41. A side note:Adapter classes class MouseHandler implements MouseListener { public void mousePressed(MouseEvent event) { ..} public void mouseClicked(MouseEvent event) {..} } • not needed – mouseReleased(MouseEvent evt) – mouseEntered(MouseEvent e) – mouseExited(MouseEvent e) • But we have to implement it anyway class MouseHandler implements MouseListener { public void mousePressed(MouseEvent event) { ..} public void mouseClicked(MouseEvent event) {..} public void mouse Released(MouseEvent event) {} // does nothing. No code Public void mouseEntered(MouseEvent e){} Public void mouseExited(MouseEvent e){} }
- 42. A side note:Adapter classes • Adaptor classes are introduced to save us from the trouble of providing empty methods – Example: • MouseAdapter is a class that consists of default implementation (do nothing) of all the three methods in MouseListener • Hence, the following is fine class MouseHandler extends MouseAdapter { public void mousePressed(MouseEvent event) { ..} public void mouseClicked(MouseEvent event) {..} } – No compiler error even though mouseReleased, mouseEntered, and mouseExited are not provided. – MouseHandler objects are MousListeners. • Most listener interfaces have adapter classes
- 43. MouseEvent Using adapter class,we now have: class MousePanel extends Jpanel { private class MouseHandler extends MouseAdapter { public void mousePressed(MouseEvent event) { // add a new square if the cursor isn't inside a square current = find(event.getPoint()); if (current == null) add(event.getPoint()); } public void mouseClicked(MouseEvent event) { // remove the current square if double clicked current = find(event.getPoint()); if (current != null && event.getClickCount() >= 2) remove(current);
- 44. MouseEvent MouseMotionHandler is alsoan inner class of MousePanel class MousePanel extends Jpanel { private class MouseMotionHandler implements MouseMotionListener { public void mouseMoved(MouseEvent event){…} public void mouseDragged(MouseEvent event) { if (current != null) { int x = event.getX(); int y = event.getY(); // drag the rectangle to center it at (x, y) current.setFrame(x - SIDELENGTH/2, y - SIDELENGTH/2, SIDELENGTH, SIDELENGTH); repaint(); } }
- 45. Objective and Outline •Objective: – Show how to write GUI programs that react to user actions. • Outline: – Java AWT event delegation model • An example – The AWT event hierarchy – Individual events • KeyEvents • MouseEvents
- 46. The Action Interface •Run ActionTest.java – One can change background color by doing one of the following: 1. Click on one of the buttons 2. Press a key : ctrl B = blue, ctrl Y = Yellow, ctrl R = red
- 47. The Action Interface Howto write the program? Do set up first class ActionPanel extends JPanel { public ActionPanel() { // add buttons for these actions add(new JButton(“Red”)); add(new JButton(“Blue”)); add(new JButton(“Yellow”)); } public void actionPerformed(ActionEvent event) { setBackground(…); repaint(); } }
- 48. The Action Interface •How to handle events? – Need a class to listen for ActionEvent from button Class Listener1 implements ActionListener { public void actionPerformed (ActionEvent e) { // action codes: change background colour } } – Also need a class to listen for KeyEvent from keystroke Class Listener2 implements KeyListener { public void keyPressed (ActionEvent e) { // action codes: change background colour } } Bad solution: “action codes” appear in two different places
- 49. The Action Interface •Better solution – Place “action codes” in one class, called action class – Associate objects of the action class to different event sources • This mechanism is provided in Swing, beyond the AWT event model. Event Soure 2 Event Source 1 Action Codes Action Class Object
- 50. The Action Interface •Next – How to write action classes? – How to associate action objects with event sources?
- 51. The Action Interface •The interface Javax.swing.Action introduced for specifying actions – Extends ActionListener • Has method: place for placing action codes void actionPerformed(ActionEvent evt) – Other methods for specifying features of the action: • setEnabled(boolean b), boolean isEnabled() • void putValue(String key, Object value) • Object getValue(String key) – (key value pairs can be used to store parameters necessary for carrying out the action, i.e. colour) • …
- 52. The Action Interface •Class AbstractAction is a default implementation of Action – The only abstract method is actionPerformed() • Instead of implementing Action, you can simply extending AbstractAction (similar to adapter class)
- 53. The Action Interface •Action class for our example: .class ColorAction extends AbstractAction { public ColorAction(String name, Icon icon, Color c) { putValue(Action.NAME, name); putValue(Action.SMALL_ICON, icon); putValue("Color", c); } public void actionPerformed(ActionEvent evt) { Color c = (Color)getValue("Color"); setBackground(c); repaint(); } } Action.NAME and Action.SMALL_ICON are used in display on buttons
- 54. The Action Interface •Make objects of the ColorAction Class Action blueAction = new ColorAction("Blue", new ImageIcon("blue-ball.gif"), Color.blue); Action yellowAction = new ColorAction("Yellow", new ImageIcon("yellow-ball.gif"), Color.yellow); Action redAction = new ColorAction("Red", new ImageIcon("red-ball.gif"), Color.red);
- 55. The Action Interface •Next – How to write action classes? – How to associate action objects with event sources?
- 56. The Action Interface •How do we associate the action objects with event sources? – The answer is easy for one event source: buttons • Associate those actions with buttons by invoke JButton constructor which takes an Action object • Add those buttons to this JPanel Class ActionPanel extends JPanel { add(new JButton(yellowAction)); add(new JButton(blueAction)); add(new JButton(redAction)); … }
- 57. The Action Interface •How do we associate the action objects with keystrokes? – InputMap provides a binding between an input event (currently only KeyStrokes are used) and an Object – ActionMap provides mappings from Objects to Actions – So, we have this solution InputMap imap = new InputMap(); imap.put(KeyStroke.getKeyStroke("ctrl Y"), "panel.yellow"); ActionMap amap = new ActionMap(); amap.put("panel.yellow", yellowAction);
- 58. The Action Interface •The solution on the previous slide does not work – We did not specify where the maps should take effect • We want them to take effect within ActionPanel and nowhere else. – How to create maps what take effect within ActionPanel?
- 59. The Action Interface •JComponent has method public final InputMap getInputMap(int condition) that returns the map used under each of the following conditions 1. JComponent.WHEN_FOCUSED When this component has keyboard focus 2. JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT When this component contains the component that has keyboard focus 3. JComponent.WHEN_IN_FOCUSED_WINDOW When this component is contained in the same window as the component that has keyboard focus
- 60. The Action Interface •JComponent has method public final ActionMap getActionMap() that returns the ActionMap used to determine what Action to fire for particular KeyStroke binding
- 61. The Action Interface •The correct solution: Class ActionPanel extends JPanel { InputMap imap = getInputMap( // since 1.3 JComponent.WHEN_ANCESTOR_OF_FOCUSED_COMPONENT); imap.put(KeyStroke.getKeyStroke("ctrl Y"), "panel.yellow"); ActionMap amap = getActionMap(); amap.put("panel.yellow", yellowAction); ….. }
- 62. The Action Interface Summary:To make action objects for multiple event sources 1. Make a class that extends the AbstractAction. 2. Make an object of that class. 3. Construct a button or menu item with that object. l The constructor will read the label text and icon from the action object.
- 63. The Action Interface 4.For action that can be triggered by keystrokes 1. Locate an appropriate component , such as a panel, within which you want the keystrokes to invoke actions. 2. Get the when_ancestor_of_focused_component input map of the component. – Make a KeyStroke object for the desired keystroke. – Make an action key object, such as a string that describes your action. – Add the pair(keystroke, action key ) into the input map. 1. Get the action map of the component. Add the pair (action key, action object) into the map.