Android开发中Looper.prepare()和Looper.loop()

　　public void handleMessage(Message msg) {

　　if (DEBUG_MESSAGES) Slog.v(TAG, ">>> handling: " + codeToString(msg.what));

　　switch (msg.what) {

　　case LAUNCH_ACTIVITY: {

　　Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityStart");

　　final ActivityClientRecord r = (ActivityClientRecord) msg.obj;

　　r.packageInfo = getPackageInfoNoCheck(r.activityInfo.applicationInfo, r.compatInfo);

　　handleLaunchActivity(r, null);

　　Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

　　}

　　break;

　　case RELAUNCH_ACTIVITY: {

　　Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityRestart");

　　ActivityClientRecord r = (ActivityClientRecord) msg.obj;

　　handleRelaunchActivity(r);

　　Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

　　}

　　break;

　　case PAUSE_ACTIVITY:

　　Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");

　　handlePauseActivity((IBinder) msg.obj, false, (msg.arg1 & 1) != 0, msg.arg2, (msg.arg1 & 2) != 0);

　　maybeSnapshot();

　　Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

　　break;

　　case PAUSE_ACTIVITY_FINISHING:

　　Trace.traceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER, "activityPause");

　　handlePauseActivity((IBinder) msg.obj, true, (msg.arg1 & 1) != 0, msg.arg2, (msg.arg1 & 1) != 0);

　　Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);

　　break;

　　...........

　　}

　　}