1. Low Level UI Components
Event Handling
Cornelius Koo - 2005

2. Low Level
• 2 Kind of interaction between User and
Canvas :
1. Commands
2. Low Level Events

3. Commands  Canvas
• Canvas is a Displayable object.
• It can accept Commands.
• It can interact with CommandListener.
Example MIDlet : TestCommandCanvas.java

4. Key Codes

5. Key Code Methods
javax.microedition.lcdui.Canvas

6. Key Detection
• To do a low level event handling, we must
detect keys and pointers.
• This Detection process is implemented
through key code methods overriding.

7. protected void keyPressed(int
keyCode) {
if (keyCode == KEY_NUM1)
...
else if (keyCode == KEY_NUM2)
...
}

8. Game Action
• A set of constant to facilitate event
handling for game appication.

10. Game Action Constants

12. Example MIDlet : TestGameAction.java

13. Converter Methods
• public int getGameAction(int
keyCode)
• public String getKeyName(int
keyCode)
• public int getKeyCode(int
gameAction)
Example MIDlet : TestLowLevelEvent.java

14. Reference
• Core J2ME Technology and MIDP. John
W. Muchow. Prentice Hall PTR, 2002.
• Enterprise J2ME: Developing Mobile
Java Applications. Michael Juntao Yuan.
Prentice Hall PTR, 2003.
• J2ME in A Nutshell. Kim Topley. Oreilly,
2002.