Lecture 19 Swing Control Programming Lecturer Prof Jim

Lecture 19 – Swing Control Programming Lecturer: Prof Jim Warren

Overview • • • Range of controls ‘hello worlds’ revisited Model v. view Tree control Customising controls

Components of a Window • Windows XP Window Components 1 -3

Swing Widgets Top-Level Containers General-Purpose Containers JPanel JFrame JScroll. Pane JDialog JSplit. Pane JTabbed. Pane JButton JCombobox JCheckbox JList JRadio. Button and Button. Group Menu JLabel 4

More Swing Widgets JFile. Chooser JTree JTable JColor. Chooser 5

Another ‘hello world’ import javax. swing. JFrame; import javax. swing. JLabel; import javax. swing. JButton; import javax. swing. JPanel; import javax. swing. JLabel; import javax. swing. JMenu. Bar; import javax. swing. JMenu. Item; import java. awt. event. Action. Event; import java. awt. event. Action. Listener; import java. awt. Border. Layout; Can also use “*” but nice to know what you’ve got Extend the root class to be a JFrame, and have it provide our button event handler public class Hello. World. Swing extends JFrame implements Action. Listener { JLabel label; public static void main(String[] args) { Hello. World. Swing frame=new Hello. World. Swing(args. length>0 ? args[0] : "Hello World"); } public Hello. World. Swing(String myhello) {. . Put the main action in the constructor

. . public Hello. World. Swing(String myhello) { label = new JLabel(myhello); get. Content. Pane(). add(label, Border. Layout. CENTER); label. set. Horizontal. Alignment(JLabel. CENTER); JButton b 0 = new JButton("Nothing"); b 0. set. Action. Command("click"); b 0. add. Action. Listener(this); JButton b 1 = new JButton("Close"); b 1. set. Action. Command("closewindow"); b 1. add. Action. Listener(this); get. Root. Pane(). set. Default. Button(b 1); JPanel bp = new JPanel(); get. Content. Pane(). add(bp, Border. Layout. PAGE_END); bp. add(b 0); bp. add(b 1); . . Border. Layout is default layout manager – more on these next lecture Different user-defined command names for the different button; both go to the action. Listener on our main object (‘this’) Make a JPanel to contain the buttons; put it at the ‘end’ of the main content pane

. . bp. add(b 1); set. Default. Close. Operation(JFrame. EXIT_ON_CLOSE); set. Size(250, 150); Centres frame relative to set. Location. Relative. To(null); whole screen final JMenu menu = new JMenu("File"); final JMenu. Item item 1 = new JMenu. Item("Exit"); item 1. add. Action. Listener(this); menu. add(item 1); JMenu. Bar menubar = new JMenu. Bar(); menubar. add(menu); set. JMenu. Bar(menubar); } set. Visible(true); public void action. Performed(Action. Event e) { if (e. get. Action. Command() == "closewindow") { set. Visible(false); dispose(); } else label. set. Text("Click!"); }; Change label’s data } Provide the method for button presses, sense the action command run the appropriate code

A ‘hello world’ applet The Java: import javax. swing. *; import java. awt. *; public class Hello. World. Applet extends JApplet { public void init() { get. Content. Pane(). add(new JLabel("Hello world!!")); } Start the action in the applet’s init method } The HTML: <applet code="Hello. World. Applet" width="100" height="30"></applet>

Separation of Model and View • Use different classes for Model and View: – Model: the data that is presented by a widget – View: the actual presentation on the screen • The data of a GUI component may be represented using several model objects, e. g. for – Displayed data (e. g. list items in JList: List. Model) – Widget state (e. g. selections in JList: List. Selection. Model) • Advantages – Data independent of views, e. g. can be displayed in several views – Model concept is integrated with event concept: changes of the model trigger well-defined events 10

List Model Example … list. Model = new Default. List. Model(); list. Model. add. Element("Alan Sommerer"); … list = new JList(list. Model); … public void action. Performed( Action. Event e) { int index = list. get. Selected. Index(); list. Model. remove(index); } … 11

Tree example private JTree tree; . . . public Tree. Demo() {. . . Default. Mutable. Tree. Node top = new Default. Mutable. Tree. Node("The Java Series"); create. Nodes(top); Give the root node to a JTree to tree = new JTree(top); display, and give the JTree to. . . JScroll. Pane tree. View = new JScroll. Pane(tree); a scroll pane to manage. . . private void create. Nodes(Default. Mutable. Tree. Node top) { Default. Mutable. Tree. Node category = null; Default. Mutable. Tree. Node book = null; category = new Default. Mutable. Tree. Node("Books for Java Programmers"); top. add(category); book = new Default. Mutable. Tree. Node(new Book. Info ("The Java Tutorial: A Short Course on the Basics", "tutorial. html")); category. add(book);

About the tree controls • The data (‘model) is a bunch of tree nodes (Default. Mutable. Tree. Node) – Any tree node has a. add that lets you give it children – You can construct the node with either • A string – that’ll be the label of that node • Any object, as long as the object implements to. String • Any object if you then override the convert. Value. To. Text of the JTree that’ll be viewing it • Construct a JTree with the root Default. Mutable. Tree. Node as its parameter to render the user control Exampe from http: //java. sun. com/docs/books/tutorial/uiswing/components/tree. html

Back to the tree example • We create our custom Book. Info object (which implements to. String for the sake of the JTree) – It also defines a URL, which we’ll use when it’s selected by the user private class Book. Info { public String book. Name; public URL book. URL; public Book. Info(String book, String filename) { book. Name = book; book. URL = get. Class(). get. Resource(filename); if (book. URL == null) { System. err. println("Couldn't find file: "+ filename); } } } public String to. String() { return book. Name; }

Responding to action on the JTree //Where the tree is initialized: tree. get. Selection. Model(). set. Selection. Mode (Tree. Selection. Model. SINGLE_TREE_SELECTION); //Listen for when the selection changes. tree. add. Tree. Selection. Listener(this); . . . public void value. Changed(Tree. Selection. Event e) { //Returns the last path element of the selection. //This method is useful only when the selection model allows a single selection. Default. Mutable. Tree. Node node = (Default. Mutable. Tree. Node) tree. get. Last. Selected. Path. Component(); if (node == null) //Nothing is selected. return; } Object node. Info = node. get. User. Object(); if (node. is. Leaf()) { Book. Info book = (Book. Info)node. Info; display. URL(book. URL); } else { display. URL(help. URL); } Our leaf nodes are books (with URLs), so go ahead and display the selected URL content (in a separate pane)

Customising tree display • You can create a cell renderer and change the icons it uses for Leaf. Icon, Open. Icon and Closed. Icon Image. Icon leaf. Icon = create. Image. Icon("images/middle. gif"); if (leaf. Icon != null) { Default. Tree. Cell. Renderer renderer = new Default. Tree. Cell. Renderer(); renderer. set. Leaf. Icon(leaf. Icon); tree. set. Cell. Renderer(renderer); }

Drawing Your Own Components • • paint(): called by the system whenever drawing is necessary – Calls paint. Component(), paint. Border(), paint. Children() – Override paint. Component() for custom look repaint(): call it if you need to trigger redrawing of components – You can give "dirty region" as argument – Asynchronously calls paint() Transparency: component does not draw all pixels in its bounds – Underlying components may need to be redrawn (slower) – Use set. Opacity(): if true then you must draw all the component‘s pixels in paint. Component() (or screen garbage) Double Buffering: component (including children) is first drawn on offscreen bitmap, then off-screen bitmap is copied to screen – Reduces flickering – In Swing used by default 17

Circle. Paint Part 1 Custom Component public class Canvas extends JComponent { class Circle { float x, y, r; Color col; } java. util. Vector<Circle> circles = new java. util. Vector<Circle>(); Circle current; public Canvas() { set. Opaque(true); set. Background(Color. white); // add mouse listeners, see next slides… } public void paint. Component(Graphics g) // see next slides… } { } 18

Circle. Paint Part 2 Event Listeners add. Mouse. Listener(new Mouse. Adapter() { public void mouse. Pressed(Mouse. Event e) { current = new Circle(); current. x = e. get. X(); current. y = e. get. Y(); current. col = Circle. Paint. color. Chooser. get. Color(); } public void mouse. Released(Mouse. Event e) { if(current!=null) circles. add(current); } public void mouse. Exited(Mouse. Event e) { current = null; } }); add. Mouse. Motion. Listener(new Mouse. Motion. Adapter() { public void mouse. Dragged(Mouse. Event e) { if(current==null) return; current. r = (float)Math. sqrt( (e. get. X() - current. x) * (e. get. X() - current. x) + (e. get. Y() - current. y) * (e. get. Y() - current. y)); repaint(); } 19 });

Circle. Paint Part 3 Paint Method public void paint. Component(Graphics g) { g. clear. Rect(0, 0, this. get. Width(), this. get. Height()); for(Circle c : circles) { g. set. Color(c. col); ((Graphics 2 D)g). fill((Shape)new java. awt. geom. Ellipse 2 D. Float( c. x-c. r, c. y-c. r, 2*c. r)); } if(current!=null) { g. set. Color(current. col); ((Graphics 2 D)g). fill((Shape)new java. awt. geom. Ellipse 2 D. Float( current. x-current. r, current. y-current. r, 2*current. r)); } } 20

Circle. Paint Part 4 Main Class public class Circle. Paint { public static JColor. Chooser color. Chooser = new JColor. Chooser(); public static void main(String[] args) { JFrame frame 1 = new JFrame("Choose the Color"); frame 1. set. Size(450, 260); frame 1. set. Default. Close. Operation( JFrame. EXIT_ON_CLOSE); frame 1. get. Content. Pane(). add(color. Chooser); frame 1. set. Visible(true); JFrame frame 2 = new JFrame("Draw Circles Here"); frame 2. set. Size(300, 300); frame 2. get. Content. Pane(). add(new Canvas()); frame 2. set. Visible(true); } } 21

Summary • Swing provides a host of familiar components (aka ‘widgets’) • You can override their default behaviours to achieve customisation • Writing action listeners (interfaces and adapters) provides interesting dynamic capabilities