Outline. More on the Swing API Graphics: double buffering and timers Model - View - Controller paradigm Applets

Transcription

1 Advanced Swing

2 Outline More on the Swing API Graphics: double buffering and timers Model - View - Controller paradigm Applets

3 Using menus Frame menus add a menu bar to the frame (JMenuBar) add menus to the menu bar (JMenu) add items to each menu (JMenuItem) implement ActionListener to handle users' choices Contextual menus JPopupMenu displayed at user's request in any place

4 Dialog windows Useful to display an information, an error, a warning or to require some input JDialog custom dialogs JOptionPane standard dialogs As long as the window is not closed, the application is blocked the dialog window is modal

5 Listener vs. Adapter Example: the MouseListener interface public void mouseentered(mouseevent e); public void mouseexited(mouseevent e) public void mousepressed(mouseevent e); public void mousereleased(mouseevent e); public void mouseclicked(mouseevent e); Any class that implements MouseListener has to define all its methods, although it may not use all of them Solution: java.awt.event.mouseadapter implements MouseListener by defining an empty block for each method any class that extends MouseAdapter can redefine only the useful methods Similar pattern for: WindowListener / WindowAdapter, MouseMotionListener / MouseMotionAdapter, KeyListener / KeyAdapter

6 Keyboard events requestfocus()indicates which component is concerned by a key press (ex: a JFrame) typically requested immediatly after the window opening KeyListener interface handles keystokes (KeyEvent) when the focus is in the targeted component: public void keypressed(keyevent evt); public void keyreleased(keyevent evt); public void keytyped(keyevent evt);

7 Composed keystrokes Associations of keys ("ctrl", "shift", "alt" + X) or keys with mouse buttons ("right click", "left click" + X) All keys are identified by constants defined in KeyEvent: VK_R, VK_BACK_SPACE, VK_TAB, VK_COMMA, VK_F3, VK_ESCAPE, etc. which key? getkeycode(); KeyEvent provides several methods to determine the modifier keys used: isaltdown(), iscontroldown(), isshiftdown(); getmodifiersex();

8 Font settings Font - represents fonts, which are used to render text in a visible way: getsize(); FontMetrics - information about the rendering of a particular font on a particular screen getheight(), getleading(), getascent(), getdescent();

9 Working with images java.awt.image abstracts the notion of bitmapped pictures (GIF, JPEG, etc.) Displaying an image: create an Image object draw it in a graphical context JAI (Java Advanced Imaging) for additional functionalities

10 Working with images Creating an Image object: try { Image taz = javax.imageio.imageio.read(new File("taz.jpg")); Image stewie = javax.imageio.imageio.read(new URL("http//link.to/pic/)); } catch(ioexception exc) {exc.printstacktrace()}; Drawing the image: g.drawimage(taz, 0, 0, this); g.drawimage(taz, 0, 200, 100, 100, this); g.drawimage(taz, 200, 0, 200, 400, Color.yellow, this); General format: boolean drawimage(image img, int x, int y, int width, int height, Color bgcolor, ImageObserver observer)

11 Double buffering Creates an in-memory drawing and then transfers it on the screen avoids the "flickering" effect Implemented by redefining the repaint() method, in order to avoid the whole drawing's deletion Swing has double buffering support built into the toolkit

12 How double buffering works public void repaint(graphics g) { } paint(g); public void paint(graphics g) { // Draw in memory on an Image object Image img = createimage(w, h); Graphics gmem = img.getgraphics(); // Make the drawing using gmem gmem.setcolor(...); gmem.filloval(...); // Transfer the drwing from the memory on the screen g.drawimage(img, 0, 0, this); gmem.dispose(); } No need to do this explicitly in Swing!

13 javax.swing.timer class Generates events (ActionEvent) at some specified time intervals Useful for animations the content of the frame is redrawn at fixed time intervals Listeners (ActionListener) needed for the events Specify the delay between the events

14 javax.swing.timer class Constructor: javax.swing.timer t = new javax.swing.timer(int ms, ActionListener doit); Usage (repaint a panel every second): javax.swing.timer t = new javax.swing.timer(1000, new ActionListener() { public void actionperformed(actionevent e) { }}); p.repaint(); Start the timer: t.start(); Stop the timer: t.stop(); Restart the timer: t.restart(); Additional methods: t.setrepeats(boolean flag); t.setinitialdelay(int initialdelay); t.isrunning();

15 Model-View-Controller Applications are generally complex so are their graphical interfaces Difficult to handle both application and GUI logic in one, big program Need to separate them handle them independently

16 Model-View-Controller The GUI class description of the graphical interface and its components the view The application class the data and the methods which describe the main functionality of the application the model The control class the set of listeners which announce the model when some events occur via the view the controller

17 Model-View-Controller the controller is a listener of the view component update Controller (Listener) the controller knows the view and the model direct association indirect association property update View (Observer) the view "observes" the model the view knows the model Model (Observable)

18 Programming with MVC Java provides some useful interfaces to map applications onto this model java.util.observer used by classes that want to be informed of changes in Observable objects update() - called whenever the observed object is changed. java.util.observable an observable object addobserver(observer o), notifyobservers(), setchanged()

19 Programming with MVC Swing provides a set of predefined models and corresponding "delegate" components Model classes data structures that can generate events when data are modified ex: DefaultButtonModel, DefaultListModel, DefaultTableModel, DefaultTreeModel Delegate components define the view (by extending JComponent) AND the control (by implementing the appropriate interfaces) ex: AbstractButton (implements ItemSelectable)

20 Using MVC with a list JList displays a list of values, on a column Data can be of any type and are not stored in the JList object String colors[] = {"red", "yellow", "blue"); JList list = new JList(colors); ListSelectionModel smodel = list.getselectionmodel(); smodel.addlistselectionlistener(new ListSelectionListener() { public void valuechanged(listselectionevent e) { // The event contains the change if (!e.getvalueisadjusting()) { System.out.println("Current selection:" + e.getfirstindex()); }} }); Or, without the model: JList list = new JList(colors); list.addlistselectionlistener(new ListSelectionListener() { public void valuechanged(listselectionevent e) { });

21 Using MVC with a list Vector colors = new Vector(); colors.add("red"); colors.add("blue"); JList list = new JList(colors); colors.add( green ); Modifying the initial vector's components doesn't reflect on the list use setlistdata(vector v); DefaultListModel model = new DefaultListModel(); model.addelement("red"); model.addelement("blue"); JList list = new JList(model); model.addelement("green"); Modifying the model's components automatically reflects on the list