Android更新UI的常用方法

Android开发中经常使用后台线程做些耗时的工作，任务完成后可以通过以下4种方法来更新ui界面。对应的函数功能说明附上，以做备份。

1、Activity.runOnUiThread(Runnable action)

Runs the specified action on the UI thread. If the current thread is the UI
     * thread, then the action is executed immediately. If the current thread is
     * not the UI thread, the action is posted to the event queue of the UI thread.

2、View.post(Runnable action)

 Causes the Runnable to be added to the message queue.
     * The runnable will be run on the user interface thread.

类似的方法包括View.postDelayed(Runnable action, long delayMillis)来延时触发ui事件

3、Handler.sendMessage(Message msg)

Pushes a message onto the end of the message queue after all pending messages
     * before the current time. It will be received in {@link #handleMessage},
     * in the thread attached to this handler.

注意，Handler必须在ui线程中初始化（Handler handler = new Handler()），或者调用Handler mainHandler = new Handler(Looper.getMainLooper())

Message创建时，推荐使用以下方法，提高创建效率：

Message msg = mainHandler.obtainMessage();
Message mst = Message.obtain();

//Message的参数解析如下
msg.what = 1000;  //消息标识。每个handler有各自的命名空间，可以不必担心冲突
msg.arg1=2;   //存放整形数据，如果携带数据简单，优先使用arg1和arg2，比Bundle更节省内存。
msg.arg2=3;   //存放整形数据

Bundle bundle=new Bundle();
bundle.putString("dd","adfasd");
bundle.putInt("love",5);
msg.setData(bundle);

msg.obj=“test”;   //用来存放Object类型的任意对象。使用messenger跨进程传消息时，需要实现Parcelable接口

发送消息的其他方法：
1）sendEmptyMessage(int what); //发送设置了what消息标志的空消息
2）sendEmptyMessageAtTime(int what, long uptimeMillis); //定时发送空消息
3）sendEmptyMessageDelayed(int what, long delayMillis); //延时发送空消息
4）sendMessageAtTime(Message msg, long uptimeMillis); //定时发送消息
5）sendMessageDelayed(Message msg, long delayMillis); //延时发送消息
6）sendMessageAtFrontOfQueue(Message msg); //最先处理消息（慎用）

4、Handler.post(Runnable r)

Causes the Runnable r to be added to the message queue.
        * The runnable will be run on the thread to which this handler is attached. 

注意，Handler必须在ui线程中初始化（Handler handler = new Handler()），或者调用Handler mainHandler = new Handler(Looper.getMainLooper())
类似的方法还有：
1）postAtTime(Runnable r, long uptimeMillis); //在某一时刻发送消息
2）postAtDelayed(Runnable r, long delayMillis); //延迟delayMillis毫秒再发送消息