Handler

Handler主要用于接受子线程发送的数据, 并用此数据配合主线程更新UI，因为更新UI只能在主线程中进行。

Handler作为线程通讯工具类。用于传递消息。它有两个队列：

• 消息队列使用sendMessage和HandleMessage的组合来发送和处理消息。
• 线程队列类似一段代码，或者说一个方法的委托，用户传递方法。使用post,postDelayed 添加委托，使用 removeCallbacks移除委托。

下例给出两个个简单用法：

• 采用Thread：

public class MainActivity extends Activity {

    private TextView mTextView;

    

    private Handler handler = new Handler() {

         

        @Override

        public void handleMessage(Message msg) {

            // 接收消息并且去更新UI线程上的控件内容

            if (msg.what == 0) {

                mTextView.setText(String.valueOf(msg.obj));

            }

            super.handleMessage(msg);

        }

    };

    

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        

        mTextView = (TextView) findViewById(R.id.text);

        

        new Thread() {

            @Override

            public void run() {

                try {

                    for (int i = 0; i < 100; i++) {

                        Thread.sleep(500);

                        Message msg = new Message();

                        msg.what = 0;

                        msg.obj = "更新后的值：" + i;

                        handler.sendMessage(msg);//向主线程的handler发消息

                    }

                } catch (InterruptedException e) {

                    e.printStackTrace();

                }

            }

        }.start();

    }

}

•  采用runable 和 postDealy:

public class MainActivity extends Activity {

    private static final String TAG_ACTIVITY = "MainActivity";

    private static int tick = 0;

    private TextView mTextView;

    private Button mbutton;

    

    private Handler handler = new Handler() {

         

        @Override

        public void handleMessage(Message msg) {

            // 接收消息并且去更新UI线程上的控件内容

            super.handleMessage(msg);

            if (msg.arg1 == 0) {

                mTextView.setText(String.valueOf(msg.obj));

            }

            

            //重新把线程加入线程队列,延迟1000ms

            handler.postDelayed(updateThread,1000);

        }

    };

    

    Runnable updateThread = new Runnable(){

        

        @Override

        public void run() {

              

            Message msg = handler.obtainMessage();

            msg.arg1 = 0;

            msg.obj = "更新后的值" + tick++;

                      

            if(10 == tick){

                //移除该线程

                handler.removeCallbacks(updateThread);

                return;

            }

            

            handler.sendMessage(msg);//向主线程的handler发消息

            Log.i(TAG_ACTIVITY, String.valueOf(msg.obj)); 

        }

    };

    

    @Override

    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        

        mTextView = (TextView) findViewById(R.id.text);

        mbutton   = (Button) findViewById(R.id.button1);

        

        mbutton.setOnClickListener(new View.OnClickListener() {

            

            @Override

            public void onClick(View v) {

                 //把线程加入线程队列

                 handler.post(updateThread);                

            }

        });

    }

}