PendingIntent中requestCode的应用

@Override
public void onUpdate(Context context, AppWidgetManager appWidgetManager,
int[] appWidgetIds) {
//
RemoteViews views=new RemoteViews(context.getPackageName(), R.layout.widget_layout);

Intent upIntent=new Intent(context, MyPlayService.class);
upIntent.putExtra("command", Command.UP);

Intent startIntent=new Intent(context, MyPlayService.class);
startIntent.putExtra("command", Command.START);

Intent pauseIntent=new Intent(context, MyPlayService.class);
pauseIntent.putExtra("command", Command.PAUSE);

Intent stopIntent=new Intent(context, MyPlayService.class);
stopIntent.putExtra("command", Command.STOP);

Intent nextIntent=new Intent(context, MyPlayService.class);
nextIntent.putExtra("command", Command.NEXT);

Log.i(TAG, "---Intent's content---");
Log.i(TAG, "upIntent--->"+upIntent);
Log.i(TAG, "startIntent--->"+startIntent);
Log.i(TAG, "pauseIntent--->"+pauseIntent);
Log.i(TAG, "stopIntent--->"+stopIntent);
Log.i(TAG, "nextIntent--->"+nextIntent);

PendingIntent upPending=PendingIntent.getService(context, 0, upIntent, 0);
PendingIntent startPending=PendingIntent.getService(context, 0, startIntent, 0);
PendingIntent pausePending=PendingIntent.getService(context, 0, pauseIntent, 0);
PendingIntent stopPending=PendingIntent.getService(context, 0, stopIntent, 0);
PendingIntent nextPending=PendingIntent.getService(context, 0, nextIntent, 0);

views.setOnClickPendingIntent(R.id.btn_up, upPending);
views.setOnClickPendingIntent(R.id.btn_start, startPending);
views.setOnClickPendingIntent(R.id.btn_pause, pausePending);
views.setOnClickPendingIntent(R.id.btn_stop, stopPending);
views.setOnClickPendingIntent(R.id.btn_next, nextPending);

for(int i=0; i<appWidgetIds.length; i++){
appWidgetManager.updateAppWidget(appWidgetIds[i], views);
}

super.onUpdate(context, appWidgetManager, appWidgetIds);
}

然后我在MyPlayService类中的onCommand方法里打印收到的command,发现无论按哪一个按钮，LogCat输出地command都是同一个值。
这和我的预期是不一样的。通过多次查找，发现问题发生在生成PendingIntent对象时，把requestCode都设为同一个值了，这就导致了上述现象。
把requestCode设为不同的值即可消除上述现象。
[code]PendingIntent upPending=PendingIntent.getService(context, 0, upIntent, 0);
PendingIntent startPending=PendingIntent.getService(context, 1, startIntent, 0);
PendingIntent pausePending=PendingIntent.getService(context, 2, pauseIntent, 0);
PendingIntent stopPending=PendingIntent.getService(context, 3, stopIntent, 0);
PendingIntent nextPending=PendingIntent.getService(context, 4, nextIntent, 0);