mainmenu.java

J2ME平台上经典的stoSwatch系统。系统架构清晰

package stopwatch;

import javax.microedition.lcdui.*;

public class MainMenu extends List implements CommandListener {
  // These are our menu choices that will be in our List.
  private static final String[] MENU_CHOICES = new String[2];
  static {
    MENU_CHOICES[0] = "Run StopWatch";
    MENU_CHOICES[1] = "Options";
  };

  // StopWatch screen.  (the screen that displays the actual stopwatch time).
  private StopWatchDisplay stopWatchDisplay = new StopWatchDisplay(this);

  // Options screen to allow user to set preferences.
  private Options optionsScreen = new Options(this);

  public MainMenu() {
    //super("StopWatch Menu", List.IMPLICIT);
    // Create a new List containing our defined menu choices.  We will title
    // our list "StopWatch Menu".
    super("StopWatch Menu",  // List title.
          List.IMPLICIT,     // List type.
          MENU_CHOICES,      // Our defined array of menu choices.
          null);             // Images.  (we're not including any images).



    try {
      jbInit();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }

  private void jbInit() throws Exception {
    // Set up this Displayable to listen to command events
    setCommandListener(this);
    // add the Exit command
    addCommand(new Command("Exit", Command.EXIT, 1));
  }

  /**
   * <p>Handle command events.</p>
   * @param command      a Command object identifying the command
   * @param displayable  the Displayable on which this event has occurred
   */
  public void commandAction(Command command, Displayable displayable) {
    // First, get the type of command that was just received.
    int commandType = command.getCommandType();

    // Now perform an action based on the type of command received.
    if (commandType == Command.EXIT) {
      // We just received the EXIT command (user just pressed EXIT), so quit
      // the MIDlet.
      StopWatch.quitApp();
    }

    else {
      // User must have selected one of the menu items.  Find out what is
      // selected and display the appropriate screen.
      String selectedItem = getString(getSelectedIndex());

      if (selectedItem.equals(MENU_CHOICES[0])) {
        // Show the StopWatch screen.
        Display.getDisplay(StopWatch.instance).setCurrent(stopWatchDisplay);
      }  else if (selectedItem.equals(MENU_CHOICES[1])) {
        // Show the Options screen.
        Display.getDisplay(StopWatch.instance).setCurrent(optionsScreen);
      }

    }

  }

  /**
    * <p>Retrieves the selected display format from the options screen.</p>
    * @return time display format
    */
   public int getDisplayFormat() {
     return optionsScreen.getDisplayFormat();
   }

   /**
    * <p>Sets the selected display format in the options screen.</p>
    * @param format  time display format
    */
   public void setDisplayFormat(int format) {
     optionsScreen.setDisplayFormat(format);
   }


  /**
    * <p>Releases references.  Used when quitting the MIDlet to make sure that
    * all variable references are null.</p>
    */
   void destroy() {
     optionsScreen = null;
     stopWatchDisplay.destroy();
     stopWatchDisplay = null;
   }


}