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13 Low Level UI Event Handling


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13 Low Level UI Event Handling

  1. 1. Low Level UI Components Event Handling Cornelius Koo - 2005
  2. 2. Low Level• 2 Kind of interaction between User and Canvas : 1. Commands 2. Low Level Events
  3. 3. Commands  Canvas• Canvas is a Displayable object.• It can accept Commands.• It can interact with CommandListener. Example MIDlet :
  4. 4. Key Codes
  5. 5. Key Code Methodsjavax.microedition.lcdui.Canvas
  6. 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. 7. protected void keyPressed(int keyCode) { if (keyCode == KEY_NUM1) ... else if (keyCode == KEY_NUM2) ...}
  8. 8. Game Action• A set of constant to facilitate event handling for game appication.
  9. 9. Game Action Constants
  10. 10. Example MIDlet :
  11. 11. Converter Methods• public int getGameAction(int keyCode)• public String getKeyName(int keyCode)• public int getKeyCode(int gameAction) Example MIDlet :
  12. 12. 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.