Handler

一、work线程向main线程发送数据（work线程发数据，main线程处理数据）

public class MainActivity extends Activity {
   
    private Button button;
    private TextView textView;
    private Handler handler;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button)this.findViewById(R.id.button1);
        textView = (TextView)this.findViewById(R.id.textView1);

        handler = new MyHandler();
        button.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View arg0) {
                  new Thread(){
                    @Override
                    public void run() {
                        super.run();
                        Thread.currentThread().getName();//获取当前线程的名字
                        Message msg = Message.obtain();
                        String s = "hello handler";
                        msg.obj = s;
                        handler.sendMessage(msg);
                    }
                           
                  }.start();    
            }
        });
    }
     
    public class MyHandler extends Handler{
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            String s = (String)msg.obj;
            textView.setText(s);
            
        }    
    }

}

　二、main线程向work线程发送数据（main线程发数据，work线程处理数据）

public class MainActivity extends Activity {

    private Button button;
    private TextView textView;
    private Handler handler;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button = (Button)this.findViewById(R.id.button);
        textView = (TextView)this.findViewById(R.id.textview);
        
        button.setOnClickListener(new OnClickListener() {
            
            @Override
            public void onClick(View v) {
                Message msg = Message.obtain();
                msg.obj = "handler2";
                handler.sendMessage(msg);
            }
        });
        new Thread(){

            @Override
            public void run() {
                super.run();
                Looper.prepare();//第一步
                handler = new Handler(){//第二步
                    @Override
                    public void handleMessage(Message msg) {
                        super.handleMessage(msg);
                        String s = (String) msg.obj;
                        System.out.println(s);        
                    }
                    
                    
                };
                Looper.loop();//第三步
            }
        }.start();    
        
    }
}

三、Handler、Looper、MessageQueue的工作原理　

handler可以在任意线程发送消息

一个线程可以有多个Handler，但是只能有一个Looper！