Handler

发送message：在工作线程给主线程发送消息

• sendMessage(Message message)
• sendEmptyMessage(int what)

处理Message：在主线程执行时，方法会被回调，建立通信基础

• handleMessage(Message msg)
  使用它来发送message和处理message

Message

工作线程与主线程的发送的消息
Message通过属性what arg1 arg2传递整型数据
setData(Bundle bundle)加载对象型数据
Message.obtain(Handler hander)
当looper将消息取出交还给另外的handler

一、发送一个空的Message，传递一个轻量的数据；使用what标识

1、继承Handler，在Activity中写一个内部类，接收消息,在这里更新UI

class MyHandler2 extends Handler{
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        textView.setText(msg.what+" ");   
 }}

2 、定义MyHandler2对象,一般为Activity的成员变量

MyHandler2 handler2=new MyHandler2();

3、在工作线程中，使用MyHandler2给UI线程发送消息

使用sendEmptyMessage(),参数为int值，传递轻量参数

 public void onClick(View view){
        new Thread(new Runnable() {
            @Override
            public void run() {
                while(i<100){
                    i++;
                    handler2.sendEmptyMessage(i);
                    try {
                        Thread.sleep(80);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }

效果图

    public class HandlerActivity_12_08 extends AppCompatActivity {
    TextView textView;
    MyHandler2 handler2=new MyHandler2();
    int i=0;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_handler_activity_12_08);
        textView= (TextView) findViewById(R.id.tvHandler_08);
    }
    public void onClick(View view){
        new Thread(new Runnable() {
            @Override
            public void run() {
                while(i<100){
                    i++;
                    handler2.sendEmptyMessage(i);
                    try {
                        Thread.sleep(80);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }).start();
    }
    class MyHandler2 extends Handler{
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            textView.setText(msg.what+" ");
        }
    }
}