baselistmidlet.java

索爱的多媒体例程,包括播放音乐,视频等

/*
 * @(#)BaseListMidlet.java	1.2 03/01/22
 *
 * Copyright (c) 2000-2003 Sun Microsystems, Inc. All rights reserved. 
 * PROPRIETARY/CONFIDENTIAL
 * Use is subject to license terms
 */

package example.mmademo;

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

/**
 * A base class for MIDLets that provide a list as display.
 * A history of displayed pages is maintained, to provide
 * user flow with automatic <i>back</i> functionality.
 *
 * @author Florian Bomers
 * @version 1.5
 */
public abstract class BaseListMidlet extends MIDlet implements CommandListener {

    // often needed commands. 
    // their functionality is provided in this class
    // but child class has to add it to the list in fillList
    protected Command exitCommand = new Command("Exit", Command.EXIT, 1);
    protected Command backCommand = new Command("Back", Command.BACK, 1);
    protected Command playCommand = new Command("Play", Command.ITEM, 1);
    protected Command selectCommand = new Command("Select", Command.ITEM, 1);

    private List list;
    private Stack history;
    
    private Displayable currDisplayable; // default: null

    public BaseListMidlet(String title) {
        history = new Stack();
        list = new List(title, Choice.IMPLICIT);
        list.setCommandListener(this);
        fillList(list);
    }
    
    /**
     * displays the last page that was displayed
     */
    public Displayable goBack() {
    	Displayable d;
	if (Utils.DEBUG) {
	    Utils.debugOut("before goBack: ("+history.size()+" elements)");
	    for (int i=history.size()-1; i>=0; i--) {
		Utils.debugOut("   "+i+": "+history.elementAt(i).toString());
	    }
	}
    	if (!history.empty()) {
	    d = (Displayable) history.pop();
	    Utils.debugOut("History: "+history.size()+" elements.");
    	} else {
    	    exit();
    	    return null;
	}
	return replaceCurrent(d);
    }

    /**
     * displays the given page. The current one is added to the history.
     */
    public Displayable go(Displayable d) {
    	Displayable curr = getCurrentDisplayable();
    	if (curr != null) {
	    history.push(curr);
	}
	if (Utils.DEBUG) {
	    Utils.debugOut("after go: ("+history.size()+" elements)");
	    for (int i=history.size()-1; i>=0; i--) {
		Utils.debugOut("   "+i+": "+history.elementAt(i).toString());
	    }
	}
    	return replaceCurrent(d);
    }

    /**
     * Replaces current displaying page with
     * the given one. The current page is not added
     * to the history.
     */
    public Displayable replaceCurrent(Displayable d) {
        getDisplay().setCurrent(d);
        if (! (d instanceof Alert)) {
	    // Alerts come back automatically
	    currDisplayable = d;
        }
	Utils.debugOut("SetCurrent: "+d.toString());
        return d;
    }   
    
    public Displayable getCurrentDisplayable() {
    	//return getDisplay().getCurrent();
    	return currDisplayable;
    } 	
    
    protected List getList() {
    	return list;
    }
    
    protected Display getDisplay() {
    	return Display.getDisplay(this);
    }

    /**
     * Child classes must implement this to insert
     * the displayed list items and commands.
     */
    protected abstract void fillList(List list);

    /**
     * Child classes must implement this in response to
     * a selection in the list
     */
    protected abstract void selectCommand(int index);


    public void startApp() {
        history.setSize(0);
        go(getList());
    }

    public void pauseApp() {}

    public void destroyApp(boolean unconditional) {
    }
    
    /**
     * Actively finish this MIDlet
     */
    public void exit() {
	destroyApp(false);
	notifyDestroyed();
    }

    /*
     * Respond to commands, including exit
     * On the exit command, cleanup and notify that the MIDlet has
     * been destroyed.
     */
    public void commandAction(Command c, Displayable s) {
        if (c == exitCommand) {
	    exit();
	} 
	else if (c == backCommand) {
	    goBack();
	}
	else if ((s == list && c == List.SELECT_COMMAND) || c == playCommand || c == selectCommand) {
	    selectCommand(getList().getSelectedIndex());
        }
    }

}