עקרונות תכנות מונחה עצמים תרגול 4 - GUI

Outline  Introduction to GUI  Swing  Basic components  Event handling

CLI VS GUI

GUI applicationsCLI applications Reactive, interactiveTransactionalProgram Flow AsynchronousTextualInput GraphicalTextualOutput YesNoMultiTasking Remains activeExitAfter Execution

GUI programming challenges  Usability  Attractiveness  Multithreading  Incremental execution  Testing And The algorithm

Elements of GUI programming  Visualization of data: Model Widgets  Visualization of commands: Buttons, pop-ups  Responding of commands: Event handling  Graphical layout: Containers, panels, layout managers  Reactiveness: Using threads safely  Separation of concerns: OOP, good design, MVC

SWING  Java’s GUI framework (Java Foundation Classes)  Extension of an older framework – AWT  Provides:  Frames, dialogs, panels, toolbars..  Graphical control widgets, from buttons to tree controls  Thread-safe events dispatching  Rich-text editing  Pluggable Look-n’-feel(PLAF)  Other goodies (accessibility, text parsing..) Official Swing Tutorial

Swing Elements  Components - Graphical widgets  Containers -Components that contain sub-components  Layout - Arrangement of components inside containers  Events - Interaction with the user  Event listeners – Objects that responds to events asynchronously  Event dispatcher – A special thread that dispatches events and re-paints the GUI  Models - Objects that hold the data and handle events for components

Swing components - hierarchy  Each component is a Java class with a fairly extensive inheritency hierarchy: Object Component Container JComponent JPanel Window Frame JFrame javax.swing java.awt java.lang

Using Swing Components  Very simple, just create object from appropriate class – examples:  JButton but = new JButton();  JTextField text = new JTextField();  JTextArea text = new JTextArea();  JLabel lab = new JLabel();  Many more classes. Don’t need to know every one to get started.

Adding components  Once a component is created, it can be added to a container by calling the container’s add method: Container cp = getContentPane(); cp.add(new JButton(“cancel”)); cp.add(new JButton(“go”)); How these are laid out is determined by the layout manager (next lesson).

JFrame  A frame contains:  Title bar  Menu bar  Content pane  The content pane is a container that represent the main area of the frame.

Example 1 Hello.jar

Jhello World! public class Hello extends JFrame { public Hello(){ super("Title Bar"); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JButton click = new JButton("This is a button"); Container cp = getContentPane(); cp.add(click); pack(); setVisible(true); } public static void main(String args[]){ Hello frame = new Hello(); }

Event handling

Events and Listeners in Swing  Input from the user in Swing is represented by Events  Events come from a Source: a component or a model  Related kinds of inputs are grouped into Listener interfaces  A listener interface contains several messages that passes events to the receiver  Each message represent a different scenario of receiving this input from the user  An Event Listener is an object whose class implements a listener interface, so it can receive events  Attaching a listener of type X to a source is done by the call : source.addXListener(listener)

Example 2 Jumper.jar

Add Action Listener public class Jumper extends JFrame implements ActionListener{ public Jumper(){ super(“Jumper"); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); JButton btn = new JButton(“Catch me!"); btn.addActionListener(this); // source.addXListener(listener) Container cp = getContentPane(); cp.add(btn); pack(); setVisible(true); public void actionPerformed(ActionEvent e) { Random rand = new Random(); int x = rand.nextInt(300); int y = rand.nextInt(300); setLocation(x, y); }

The Event object  All event classes in Swing extends the EventObject class.  This class contains the method getSource( ) that returns the object which was the source of the event  Events sub-classes usually also contain data related to specific event.

Event Listener Example: Action Listener

Event Listener Example: Mouse Listener

Listening to an event

Example 3 Convertor.jar

public class Convertor extends JFrame implements ActionListener { private static double DOLLAR_RATE = 3.943; private JButton convertButton; private JButton resetButton; private JLabel resultLabel; private JTextField valueInput; private double value; public Convertor(){ super("Convertor"); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); value = 0; // Initiate label and text field. valueInput = new JTextField(); valueInput.setColumns(10); valueInput.setText( value + ""); resultLabel = new JLabel(value + " $ is "+ convert() + " Shekel"); // Create buttons convertButton = new JButton("Convert"); resetButton = new JButton("Reset");

// Add action listeners convertButton.addActionListener(this); resetButton.addActionListener(this); // Add all objects to Content Pane getContentPane().setLayout(new FlowLayout()); getContentPane().add(resetButton); getContentPane().add(valueInput); getContentPane().add(convertButton); getContentPane().add(resultLabel); pack(); setVisible(true); {

public void actionPerformed(ActionEvent e) { if (e.getSource().equals(convertButton)){ updateValue(); } if (e.getSource().equals(resetButton)){ setValue(0); } updateView(); { private void setValue(double v) { this.value = v; } private double convert() { return value*DOLLAR_RATE; { private void updateValue(){ this.value = Double.parseDouble(valueInput.getText()); } private void updateView(){ resultLabel.setText(value +" $ is " + convert() + " Shekel " ); valueInput.setText(value +""); pack(); {