plik

Języki Programowania

Graficzny interfejs użytkownika

GUI Principles



GUI

– Graphical User Interface



GUI’s are a good target for OO design



GUI’s main elements



Components

: GUI building blocks.



buttons, menus, sliders, etc.



Layout

: arranging components to

form a usable GUI.



using layout managers.



Events

: reacting to user input.



button presses, menu selections, etc.

 There are some tools for convenient GUI-based design



JBuilder, Eclipse, NetBeans

Java GUI classes



AWT

(Abstract Window Toolkit) (java.awt.*)

 pierwszy szkielet GUI dla Javy (Java 1.1)


pewne uzależnienia o implementacji języka



problemy implementacji na różnych platformach



Swing

(javax.swing.*)

 kolejne GUI wprowadzone od wersji Java 1.2
 zawiera cechy AWT i dodatkowe rozszerzenia


poprawione komponenty (bez uzależnienia się od implementacji)



mechanizmy do zmiany GUI w czasie działania programu



SWT

(Standard Widget Toolkit; from Eclipse)

AWT and Swing

AWT

was the original platform-dependent layer of

Java to build GUI’s.

Swing

(platform independent layer) was added later.

Swing is part of JFC (

Java Framework Collection

Event-driven programming

- sterowanie zdarzeniami

 GUIs are

event-driven programs

: external events cause

methods to be executed



Components (komponenty)

: objects we create which

have a screen presence (e.g. controls, window panes),
and with which the user interacts (e.g. buttons).



Events (zdarzenia)

: when a user interacts with a

component, java creates an event object (which records
the source)



Listeners

(„słuchacze”)

: Objects we create which

respond to events. A listener has a handler method,
which Java invokes when the event occurs.

Container (window) with
component (button)

All this for one button click ...

user

user clicks
button

event object
is generated

ae:ActionEvent

event is
queued
for action

Listener objects

... do something

pętla obsługi

zdarzeń

: remove from

queue, invoke

handlers in

registered

listeners

... which requires:

 In the program:

 write a class that creates a window and a

JButton

, adds the

JButton to the window, makes the window visible

 write listener classes (implements

ActionListener

) with handler

method (ActionPerformed)

 create listener objects and register them with the JButton

 At runtime:

 user clicks the button
 Java creates the ActionEvent object
 Java adds object to a queue of events
 Java repeatedly



takes object from queue



identifies their listeners



invokes each listener's handler with event as input

A first GUI ...

import

java.awt.*;

import

java.awt.event.*;

import

javax.swing.*;

public

class

SimplePanel

extends

JPanel {

private

JButton btn;

public

SimplePanel() {

super

();

btn =

new

JButton("Click me!");

add(btn);
ActionListener lstnr =

new

SimpleButtonListener();

btn.addActionListener(lstnr);
}

import AWT, AWT.event
and Swing packages

call to JPanel constructor

create a button

add it to the panel

create a listener

public

static

void

main(String[] args) {

JFrame frm =

new

JFrame("A simple GUI");

Container contentPane = frm.getContentPane();
JPanel pnl =

new

SimplePanel();

  contentPane.add(pnl);
  frm.setBounds(100, 300, 400, 200);
  frm.setVisible(true);
}

}

SimplePanel continued

create a frame

get a handle on it

create a panel

add panel to frame

position it on screen

make it visible!

SimpleButtonListener

import

java.awt.event.*;

public class

SimpleButtonListener

implements

ActionListener {

private

int

count;

public

SimpleButtonListener() {

}

public

void

actionPerformed(ActionEvent ae) {

count++;
System.out.println(count);
}
}

tell Java it
is a Listener

state what happens
when the button is
pressed

That’s it ...

try do it in BlueJ yourself

you can also use JDK ...

no changes in source code needed

after 10 clicks

Components in the GUI

 the GUI needs 2

JButto

, a subclass of

JPanel

and



javax.swing.JTextField



allows display / entry / edit of a line of text



constructor specifies initial value (and number of columns)



has methods

setText(...), getText(...),

etc.



javax.swing.JLabel



allows display of text / images



user cannot edit them



constructor supplies initial text



has methods

setText(...), getText(...),

etc.

JFrame

JPanel (in the ContentPane
of the JFrame)

JButton

JTextField

JLabel

Components in the GUI

GUI Containers

 some components are

containers



can have other components added to them

 JPanel

is a container

– it has

JButton

s added to it



a container can have other containers added to it

 JFrame

is a container

– it has a

JPanel

added to it (via its

content pane)

 (in fact, in Swing, all components are containers)

1. The Window Listener

 we mentioned that we could associate a listener with the

JFrame

 the WindowListener interface specifies 7 methods, which

respond to changes in a window's state:

 windowActivated(...)

: window is set to be active

 windowClosed(...)

: window is closed by program

 windowClosing(...)

: window closed by user

 windowDeactivated(...)

: window is no longer active

 windowDeiconified(...)

: window is restored to normal

 windowIconified(...)

: window is minimised

 windowOpened(...)

: window opened for first time

2. Using WindowAdapter

 instead of laboriously typing default methods for the

WindowListener

, we can instead inherit from

WindowAdapter



implements

WindowListener



supplies 7 default methods

 all we need to do is override the particular methods we

want

Good news for GUI developers



Even simple GUI seems to be very complicated to
develop in Java



Fortunetely, we have a number of IDEs (

Integrated

Development Environments

) to do it using a mouse and

„drag and pop” method

 JBuilder (from

Borland

)

 JCreator
 Eclipse
 NetBeans (

Sun Microsystems

)

NetBeans