android handler和message的常用方法

1.

    private class AsyncServiceHandler extends Handler {

        AsyncServiceHandler(android.os.Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(Message msg) {
                          ...........................................
                     case WifiManager.ENABLE_TRAFFIC_STATS_POLL: {
                          ...........................................

}

private AsyncServiceHandler mAsyncServiceHandler;

mAsyncServiceHandler = new AsyncServiceHandler(wifiThread.getLooper());

Message msg;

 msg = Message.obtain(mAsyncServiceHandler, WifiManager.ENABLE_TRAFFIC_STATS_POLL, 0, 0);

msg.sendToTarget();

這裡Message.obtain表示obtain Message object from the global pool, 第一個參數表示發送的handler目標，第二個為what, 第三個為arg1, 第四個為arg2,看函數原型就知道了：

    public static Message obtain(Handler h, int what, int arg1, int arg2) {
        Message m = obtain();
        m.target = h;
        m.what = what;
        m.arg1 = arg1;
        m.arg2 = arg2;

        return m;
    }
最後調用msg.sendToTarget()將訊息發送到AsyncServiceHandler中，AsyncServiceHandler繼承並重寫handleMessage方法，在handleMessage中根據switch處理接收到的訊息

2.

 Handler mhandler = new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            int what = msg.what;

            switch(what){

                case 2:

                          String shortFileNames = msg.getData().getString("packagename");

                           ........................自己的處理方法............................

            }

};

Message msg = mhandler.obtainMessage();
Bundle b = new Bundle();// 存放資料
msg.what = 2;
b.putString("packagename", shortfileNames.get(i));
msg.setData(b);
mhandler.sendMessage(msg); // 向Handler發送訊息,更新UI

原理和上面1其實是一樣的，也是從訊息池中擷取message,這樣不用新new一個，可以節省資源，new Bundle()用來存放資料，然後mhandler.sendMessage將訊息發送到Handler中