lecture-07-gui and event handling

8/12/2019 Lecture-07-GUI and Event Handling

1/40


2/40

The Robert Gordon University K. Hui 2010-2011

Content GUI Programming

AWT & Swing Creating Frames Drawing in a Frame

Event Handling The Java Event Delegation Model Using Interfaces Using Adapter Classes


3/40


4/40


Problems of AWT implement the common features of native

window systems but not everything

more advanced graphical facilities have to be builtfrom AWT

heavy-weight components that rely on nativeimplementation

also inherits the bugs

look-and-feel is different on different platform


5/40


6/40


7/40


AWT & Swing Class HierarchyAWT & Swing are collections of

related classes

use OO relationship of:

composition

association inheritance


8/40


Packages Needed AWT Classes

in java.awtpackage

Swing Classes in javax.swingpackage

main packages/ classes to import java.awt.*

java.awt.event.* javax.swing.*

javax.swing.event.*

AWT

stuff

Swingstuff


9/40


The javax.swing.JFrame

Class the top-level window

a frame

can contain other graphic components

JFramehas some basic functionalities

usually define your own application-specificJFrameby inheritance

i.e. extends JFrame


10/40


Super Classes of JFrame

java.lang.Object

java.awt.Component

java.awt.Container

java.awt.Window

java.awt.Frame

javax.swing.JFrame

all UI components aresubclasses of Component

components

that cancontain/storeother

components

a heavy-weightinterface to

theunderlying

windowsystem

a windowwith title& border


11/40


The Simplest GUI Application contains 2 classes:

MyGuiFrame:a specialised frame

TestMyGuiFrame: usesMyGuiFrame

javax.swing.JFrame

MyGuiFrame

TestMyGuiFrame

main(argv:String[])


12/40


MyGuiFrame&TestMyGuiFrame

import javax.swing.*;

public class MyGuiFrame extends JFrame

{

} //end class MyGuiFrame

public class TestMyGuiFrame

{

public static void main(String argv[])

{

MyGuiFrame f=new MyGuiFrame();

f.setSize(200,200);f.setTitle("TestMyGuiFrame App");

f.setVisible(true);

} //end method main

} //end class TestMyGuiFrame

MyGuiFrame.java

TestMyGuiFrame.java

Create frameobject, setsize & title,then display

frame.


13/40


MyGuiFrame &

TestMyGuiFrame Version 2import javax.swing.*;

public class MyGuiFrame2 extends JFrame

{

public MyGuiFrame2()

{

this.setSize(200,200);

this.setTitle("TestMyGuiFrame App");

this.setVisible(true);

} //end constructor

} //end class MyGuiFrame2

public class TestMyGuiFrame2{


{

new MyGuiFrame2();

} //end method main

} //end class TestMyGuiFrame2

Having aconstructor.

Fix window size,

set title anddisplay frame assoon as frame

object is created.

Just create frameobject.


14/40


MyGuiFrame &

TestMyGuiFrame Version 3import javax.swing.*;public class MyGuiFrame3 extends JFrame

{

public MyGuiFrame3(int width,int height,String title)

{

this.setSize(width,height);this.setTitle(title);

this.setVisible(true);

} //end constructor

} //end class MyGuiFrame3

public class TestMyGuiFrame3{


{

new MyGuiFrame3(200,200,"TestMyGuiFrame App");

} //end method main

} //end class TestMyGuiFrame3

Constructorallows differentsizes & title. Stilldisplay frame by

default.

Create frame withgiven parameter

values.


15/40


Another Design have "main" defined in the frame class

make the frame class runnable

javax.swing.JFrame

MyGuiApp

main(argv:String[])


16/40


17/40


Details ofMyGuiApp

it is a subclass of JFrame

the constructor is implicit

it has a "main" the static/class-level method "main" creates an

instance ofMyGuiApp

it calls setSize(int,int)from java.awt.Component

setTitle(string)from java.awt.Frame

setVisible(boolean)from java.awt.Component


18/40


Questions

How do you know which UI component (class)to use?

How do you know which method to call to dowhat?

experience!

look at the API

some IDE have a built-in GUI builder

e.g. NetBeans

*** NOT in your assessment!


19/40


Drawing Graphics inside aJFrame

override the methodpublic void paint(Graphics g)

paint()is called whenever a re-painting ofthe frame is needed, including:

resize

move

obscured & revealed

the call topaint()is automatically done

by the system, not by you!


20/40


Drawing Text (Graphically) ina JFrameimport javax.swing.*;

import java.awt.*;

public class HelloWorldFrame extendsJFrame

{

public void paint(Graphics g)

{

super.paint(g);

g.setColor(Color.BLUE);g.drawString("Hello World!",75,100);

} //end method paint

// main method here

} //end class HelloWorldFrame

a very importantcall tothe superclass paint()

method


21/40


Drawing Text (Graphically) ina JFrame

overridepublic void paint(Graphics g)fromjava.awt.Container

need to call super.paint(g) Why? See the API!

the Graphicsobject allows you to:

set colour by: setColor()

set font by: setFont()

NB: Graphicsis an abstract class in java.awt


22/40


23/40


Java Event Delegation Model

events something happened

involve 3 kinds of object: event sources event listeners events

source listener

event


24/40


Event Sources

generates events(object)

usually existing GUI components

have methods to register eventlistenersto events

an event sourcenotifies allregistered event listenerswhen aneventoccurs


25/40


Event Listeners

objects that implements a listenerinterface

so that it qualifies to handle events respond to events

listen to/catch events

implement all (abstract) methods oflistener interface to handle the events customise these methods to change

listener objects behaviour


26/40


Different Kinds of Event action events

java.awt.event.ActionEvent

when a component is activiated (e.g. button)

adjustment events java.awt.AdjustmentEvent

when a scroll bar is moved

container events

java.awt.event.ContainerEvent when the content of a container is altered

focus events java.awt.event.FocusEvent

when a component gains/loses the keyboard focus


27/40


Different Kinds of Event(cont'd) window events

java.awt.WindowEvent

when a window is changed

key events java.awt.KeyEvent

when a key is pressed

mouse events java.awt.MouseEvent when the mouse is moved/clicked

all are subclasses of

java.awt.AWTEvent


28/40


To Handle Events in a GUI

1. create event source object usually a GUI component (e.g. a button)

2. create event listener object must implement a listener interface

must implement event handling method(s) in theevent listenerto handle the events(object)

3. register event listener objectas an eventlistener of event source objecton a type ofevent


29/40


TheWindowListener

Interface

defined in the java.awt.eventpackage

listen to window events

declare abstract methods:public void windowActivated(WindowEvent e)

public void windowClosing(WindowEvent e)

public void windowClosed(WindowEvent e)

public void windowDeactivated(WindowEvent e)

public void windowDeiconified(WindowEvent e)

public void windowIconified(WindowEvent e)

public void windowOpened(WindowEvent e)


30/40


Class Hierarchy of theCloseableHelloWorldFrame

javax.swing.JFrame

CloseableHelloWorld

main(argv:String[])

windowActivated(e:WindowEvent)windowClosing(e:WindowEvent)windowClosed(e:WindowEvent)

java.awt.event.WindowListener


31/40


A Closeable Frame

implement theWindowListenerinterface to handle window events

// import statementspublic class

CloseableHelloWorld extendsJFrame implements

WindowListener{

//methods here

}

make sure youknow what toimport


32/40


The Constructor

when a CloseableHelloWorld (alsoa JFrame) object is created,

addWindowListener(this)registers the object itself as its ownwindow event listener

public CloseableHelloWorld()

{

this.addWindowListener(this);

}


33/40


34/40


Adapter Classes

instead of having an object as itsown event listener, it can have a

dedicate object to handle theevents

extend the adapter classes java.awt.event.WindowAdapter


35/40


Class Hierarchy

javax.swing.JFrame

CloseableHelloWorld2

main(argv:String[])

java.awt.event.WindowAdapter

HelloWorldCloser

windowClosing(e:WindowEvent)


36/40


The HelloWorldCloser

Class

//import statements

public class HelloWorldCloserextends WindowAdapter

{public voidwindowClosing(WindowEvent e)

{

System.exit(0);

} //end method windowClosing

} //end class HelloWorldCloser

exit program

when this methodis invoked

event handler

for window-closing event


37/40


CloseableHelloWorld

Version 2

//import statements

public class CloseableHelloWorld2extends javax.swing.JFrame

{public CloseableHelloWorld2()

{

this.addWindowListener(newHelloWorldCloser());

}

//main, etc.

} //end class HellowWorldApp

Create event listenerobject & register it as

the event handler of thisevent source object.

In constructor

of frame,create and

register eventhandler object


38/40


Interface vs Adapter Classes

adapter class advantage:

empty methods already defined in thesuperclass (WindowAdapter)

only need to override methods youwant

don't have to implement all methods(as in an interface)


39/40


What now?

add UI components to the frame

e.g. buttons, menu items, etc.

How to respond when button ispressed?

components (e.g. buttons) generateevents

implement the appropriate event

handlers


40/40

K H i 2010 2011

Summary

develop GUI by extending JFrame

handling events involves the event source object the event object

the event listener/handler object

implement event handler by: implement interfaces

extending adapter classes

lecture-07-gui and event handling

Documents