[german]Bei der recherche nach den MIDlet-States erstellte ich folgendes Programm. Vielleicht ist es für Andere ((Kommentare willkommen)) hilfreich. Außerdem fand ich folgende Dinge heraus:

• Nokia 6300 (Symbian Series 40) kennt keinen pausierten Status für MIDlets
• SonyEricsson K800i kann MIDlets pausieren (aus dem MIDlet und auch aus dem Telefon)
• Wenn das K800i das MIDlet in den Hintergrund packt, werden weder pauseApp() noch startApp() aufgerufen – das Midlet läuft also vollständig im Hintergrund.
• K800i kann nur dann wirklich pausieren, wenn man in der pauseApp() das currentDisplay auf null setzt (display.setCurrent(null);). Ein einfaches Aufrufen von notifyPaused() funktioniert nicht.
• Suns Wireless Toolkit reagiert auf pauseApp() und notifyPaused() gleichermaßen.

[/german]
[english]While exploring the MIDlet-States i created the following program. Maybe it is useful ((Comments welcome *hint*)) for others. In writing the program the following peculiarities were found:

• Nokia 6300 (Symbian Series 40) apparently does not know a paused-state
• SonyEricsson K800i can pause MIDlets (either from the MIDlet itself or by the phone’s request)
• If the telephone sets the midlet to paused state neither pauseApp() nor startApp() are called. Therefore the MIDlet runs the same way as if it was not paused.
• K800i can only pause the MIDlet if you set the current display to null inside pauseApp() (display.setCurrent(null);). Simply calling notifyPaused won’t do the trick.
• Suns Wireless Toolkit reacts to pauseApp() and notifyPaused().

[/english]

Download

Source-Files and compiled MIDlet as a zip-file (4KB)

StateChanges.java

import java.util.Timer;
import javax.microedition.lcdui.*;
import javax.microedition.midlet.*;

/**
 * DEMO-Midlet to try State-Changes initiated by AMS and User-interaction
 * Feel free to use and modify this.
 * @author http://amenthes.de
 * @link http://amenthes.de/
 * This is free code. Use, Change and redistribute it to your liking.
 */
public class StateChanges extends MIDlet implements CommandListener {
	// all my commands
	public static final Command PAUSEAPP = new Command("pauseApp",Command.SCREEN,40);
	public static final Command NOTIFYPAUSE = new Command("notifyPause",Command.SCREEN,40);
	public static final Command DESTROYAPP = new Command("destroyApp",Command.EXIT,40);
	public static final Command NOTIFYDESTROYED = new Command("notifyDestroyed",Command.EXIT,40);
	public static final Command STARTAPP = new Command("startApp",Command.ITEM,40);
	public static final Command RESUMEREQUEST = new Command("resumeRequest",Command.ITEM,40);

	// other stuff
	private Display display;
	private TextBox tb = new TextBox("State-Changes","",2000,TextField.ANY);
	private Timer timer = new Timer();

	protected static StateChanges sc = null;

	public StateChanges() {
		sc = this;
		display = Display.getDisplay(this);
		tb.addCommand(PAUSEAPP);
		tb.addCommand(NOTIFYPAUSE);
		tb.addCommand(DESTROYAPP);
		tb.addCommand(NOTIFYDESTROYED);
		tb.addCommand(STARTAPP);
		tb.addCommand(RESUMEREQUEST);
		tb.setCommandListener(this);
	}

	/*
	 * destroyApp, pauseApp and startApp are the abstract methods of MIDlet.
	 * They are called by your device (cellphone, for example). You can also
	 * call them in your application (as we do here with the commands)
	 *
	 * These functions should _prepare_ the state-change.
	 */
	protected void destroyApp(boolean unconditional) throws MIDletStateChangeException {
		addLine("destroyApp(" + unconditional + ") was called");
	}
	protected void pauseApp() {
		addLine("pauseApp was called");
		timer.schedule(new ResumeTask(this), 5000);
		display.setCurrent(null);
	}
	protected void startApp() throws MIDletStateChangeException {
		display.setCurrent(tb);
		addLine("startApp was called");
	}

	/*
	 * As you can see we prepare the state-change before actually notifying the AMS.
	 * you will see a difference in behaviour when calling the different
	 */
	public void commandAction(Command c, Displayable d) {
		if (c == PAUSEAPP) {
			pauseApp();
			notifyPaused();
		} else if (c == NOTIFYPAUSE) {
			notifyPaused();
		} else if (c == DESTROYAPP) {
			try{destroyApp(false);} catch (MIDletStateChangeException unhandled) {}
			notifyDestroyed();
		} else if (c == NOTIFYDESTROYED) {
			notifyDestroyed();
		} else if (c == STARTAPP) {
			try { startApp(); } catch (MIDletStateChangeException unhandled) {}
		} else if (c == RESUMEREQUEST) {
			resumeRequest();
		}
	}

	/**
	 * This function will give you output in two forms: on your Console (if you are running an emulator) and on the device's screen.
	 * @param line What text should be displayed?
	 */
	private void addLine(String line) {
		System.out.println(line);
		String current = tb.getString();
		tb.setString(current + "\n" + line);
	}
}

ResumeTask.java

import java.util.TimerTask;
import javax.microedition.midlet.MIDlet;

public class ResumeTask extends TimerTask {
	private MIDlet midlet;
	public ResumeTask(MIDlet parentMidlet) {
		super();
		midlet = parentMidlet;
	}
	public void run() {
		midlet.resumeRequest();
	}
}