Event Handling of MIDlet

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Event Handling of MIDlet

• Yin-Hsong Hsu
• Oct. 2003

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Agenda

• Life Cycle of MIDlet
• Input Interface of Physical Machine
• Event Handling of MIDlet

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(No Transcript)
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Program Structure of MIDlet

• Your MIDlets must inherit from class
  javax.microedition.midlet.MIDlet
• Abstract methods in class MIDlet
• startApp() signals the MIDlet that it has
  entered the Active state
• pauseApp() signals the MIDlet to stop and enter
  the Pause state
• destroyApp() signals the MIDlet to terminate
  and enter the Destroyed state

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Life Cycle of MIDlets
The methods are called by Java Application
Manager
Constructor New myMIDlet()
Pause
startApp()
destroyApp()
pauseApp()
Active
Destroyed
destroyApp()
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• MIDlet can also change its own state by
  signaling Java Application Manager

Pause
notifyDestroyed()
resumeRequest()
notifyPause()
Active
Destroyed
notifyDestroyed()
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Basic Operating Procedure
JAM call startApp()
MIDlet entering Active state
Get the Display object
Set current screen to display
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import javax.microedition.midlet.  public class
HelloMIDlet extends MIDlet implements
CommandListener public HelloMIDlet()
display Display.getDisplay(this)
public void startApp()
display.setCurrent(myForm)
public void pauseApp() public void
destroyApp(boolean unconditional)
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Input Interface in Physical Machines

• Different machines behaves differently
• Programmers does not have to worry about this
• KVM handles the differences and mappings

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Control Key
Navigation Key
Touch Panel On LCD Screen
Soft Button
Alphanumeric Key
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Event Handling

• Event
• Event Handler
• Callback method
• Interfaces in Java

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Interface in Java

• What Are Interfaces?
• An interface is a collection of method
  definitions (without implementations) and
  constant values
• Defining an Interface
• Implementing an Interface
• Using an Interface as a Type

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What Are Interfaces?

• Useful for
• Capturing similarities between unrelated classes
  without forcing a class relationship
• Declaring methods that one or more classes are
  expected to implement
• Revealing an object's programming interface
  without revealing its class
• Interfaces do not provide multiple Inheritance
• Differences from multiple inheritance
• You cannot inherit variables from an interface
• You cannot inherit method implementations from an
  interface.
• The interface hierarchy is independent of a the
  class hierarchy. This is not true for multiple
  inheritance

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Defining an Interface

• The interface declaration  
•   public interface InterfaceName extends 
  listOfSuperInterfaces . . .
• The interface body
• All constant values defined in an interface are
  implicitly public, static, and final
• All methods declared in an interface are
  implicitly public and abstract
• Interfaces and their methods are implicitly
  abstract

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Implementing an Interface

• A class that implement the interface
• A class declares all of the interfaces that it
  implements in its class declaration
• A class implements one or more interfaces use the
  key word implements followed by a comma-delimited
  list of the interfaces implemented by your class

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Using an Interface as a Type

• You can use interface names anywhere you'd use
  any primitive data type name or any other
  reference data type name
• An example

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interface CellAble     void draw()     void
toString()     void toFloat()
class MyCell implements CellAble     void
draw()       ...     void toString()
... void toFloat() ...
class Row     private CellAble contents
            . . .     void setAt(CellAble ca,
int index)             ca.draw()        
...         ca.toString()         ...    

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Types of Event Handling for MIDlet

• High-level event handling
• Most general events
• Low-level event handling
• Key pressed, or touch screen
• Event handling for painting event
• Runnables run() method

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Handling High Level Events

• Two high-level event handling interfaces in
  MIDlet
• CommandListener
• For Command in javax.microedition.lcdui
• commandAction(Command c, Displayable d)
• ItemStateListener
• For state changed, such as Item in
  javax.microedition.lcdui
• itemStateChanged(Item item)
• CommandListener
• An example HLEventMIDlet.java

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• Steps of event handling
• Register event handler
• Event occurs
• Event listener is notified, and then the event
  handler is invoked
• Unicast mechanism
• Only one listener can be registered to an event
  source at the same time

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public HLEventMIDlet() display
Display.getDisplay(this) exitCommand new
Command("Exit", Command.SCREEN,1) info1Command
new Command("Info1", Command.SCREEN,2) info2Co
mmand new Command("Info2", Command.SCREEN,2)
3 commands
public void startApp() TextBox t new
TextBox("Hello MIDlet", "Test string", 256,
0) t.addCommand(exitCommand) t.addCommand(info
2Command) t.addCommand(info1Command) t.setCom
mandListener(this) display.setCurrent(t)
Add 3 commands
Set command listener
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implements the interface
public class HLEventMIDlet extends MIDlet
implements CommandListener public
void commandAction(Command c, Displayable s)
if (c exitCommand)
notifyDestroyed() else if (c info1Command)
notifyDestroyed()
Handling the event
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• Running the MIDlet using different phone
  emulators
• Three commands, how about 2 commands? 4 commands?
• new Command("Exit", Command.SCREEN,1)

Label to be displayed on screen
Command type
Command priority
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• Label of the command
• Command types
• Command.BACK, Command.CANCEL, Command.EXIT,
  Command.HELP, Command.ITEM, Command.OK,
  Command.SCREEN, Command.STOP
• Priority of the command

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• Another example ListEventMIDlet.java

public void startApp() List l new
List("Test Item",Choice.IMPLICIT)
l.setCommandListener(this) l.append("Test
1",null) l.append("Test 2",null)
l.addCommand(exitCommand)
display.setCurrent(l)
public void commandAction() if (c
exitCommand) notifyDestroyed() else
List tmp (List) s switch(tmp.getSelectedI
ndex()) case 0 display.setCurrent(new
TextBox("Test1","Test1",256,0))
break case 1 display.setCurrent(new
TextBox("Test2","Test2",256,0))
break
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ItemStateListener

• Implements ItenStateListener
• setItemStateListener()
• ItemStateChanged()
• An example TFEventMIDlet.java

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public void startApp() Form f new
Form("Form") TextField tf new
TextField("Input","Origin",25,TextField.ANY)
f.append(tf) f.setItemStateListener(this)
display.setCurrent(f)
public class TFEventMIDlet extends MIDlet
implements ItemStateListener . public
void itemStateChanged(Item item)
TextField tmp (TextField) item
tmp.setString("Changed")
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Low-Level Event Handling

• Class Canvas
• Derived from class Displayable
• Command is allowed
• ItemState is not allowed
• Two kinds of low-level events
• Key events
• Pointer events

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• Key Event
• keyPressed(int keyCode)
• keyReleaseed(int keyCode)
• keyRepeated(int keyCode)
• keyCode
• KEY_NUM0, KEY_NUM1, KEY_NUM2, , KEY_NUM9,
  KEY_STAR, KEY_POUND
• An example LLEventMIDlet.java

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class MyCanvas extends Canvas String action
"" public void paint(Graphics g)
//???? g.setColor(255,255,255)
g.fillRect(0,0,getWidth(),getHeight())
g.setColor(0,0,0) if(hasRepeatEvents())
//?????????? g.drawString("Repeat",10,10,0)
else g.drawString("NonRepeat",10,10,0)
g.drawString(action,10,20,0)
protected void keyPressed(int keyCode)
action KP (char)keycode repaint()
protected void keyReleased(int keyCode) .
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• Game Design -- Key code
• Not all phone has the same key placement
• May cause problems in games
• Abstract key map for games
• UP, DOWN, LEFT, RIGHT, FIRE, GAME_A, GAME_B,
  GAME_C, GAME_D
• getGameAction(keyCode)
• Convert KeyCode to its corresponding GameCode
• getKeyCode(gameCode)
• Convert GameCode to its corresponding KeyCode

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• Pointer Event
• pointerPressed(int x, int y)
• pointerReleased(int x, int y)
• pointerDragged(int x, int y)
• hasPointerEvents() to check whether touch screen
  is supported
• An example TouchEventMIDlet.java

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if(hasPointerEvents()) g.drawString("Point",10,
10,0) else g.drawString("NonPoint",10,10,0)

protected void pointerPressed(int x,int y)
action "x" x "" "y" y
repaint() protected void pointerReleased(int
x,int y) action "x" x "" "y" y
repaint() protected void pointerDragged(int
x,int y) action "x" x "" "y" y
repaint()
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More Examples

• An Example Using Class Date
• DateExample.java
• Two listeners
• Class Date
• Selecting different display format
• Displaying date

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TextBox1
TextBox2
SetDateType DisplayDate Exit
SetUSAType SetNormalType Exit

• Set date format
• Set string to TextBox1
• Set current to TextBox1

1.Get date 2.Prepare string 3.Set string to
TextBox1
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• Random Number Generation
• RanGen2.java
• Class Random supports different methods in J2SE
  and MIDP

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• Lottery Using Random Number
• Lottery.java
• Application Properties
• Get Application Property
• Set Application Property
• String v.s. StringBuffer

Form
StringItem
More Exit