Android Messaging Mechanism

Android Messaging Mechanism

Handler is a message processing mechanism provided in android. It is often used to send messages in sub-threads, and obtain and process messages in the main thread.

The basic mechanism is as follows:

Handler

• Process messages:

Handler h = new Handler(){
    
    
    @Override
    public void handlerMessage(Message msg) {
    
    
        // 对消息进行处理
        super.handlerMessage(msg);
        
    }
}

• Send a message:

  <handler>.sendMessage(Message msg)<handler>.sendEmptyMessage (int what)
  

  • what: message ID

Example:

package com.mingrisoft;

import android.app.Activity;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ProgressBar;
import android.widget.Toast;

public class MainActivity extends Activity {
    
    

    final int TIME = 60;    //定义时间长度

    final int TIMER_MSG = 0x001;    //定义消息代码

    private ProgressBar timer;    //声明水平进度条

    private int mProgressStatus = 0;    //定义完成进度

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    
    
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        timer = (ProgressBar) findViewById(R.id.timer);      //获取进度条组件
        handler.sendEmptyMessage(TIMER_MSG);    //发送消息，启动进度条
    }
    Handler handler = new Handler() {
    
    
        @Override
        public void handleMessage(Message msg) {
    
    
            //当前进度大于0
            if (TIME - mProgressStatus > 0) {
    
    
                mProgressStatus++;         //进度+1
                timer.setProgress(TIME - mProgressStatus);            //更新进度条的显示进度
                handler.sendEmptyMessageDelayed(TIMER_MSG, 1000);    //延迟一秒发送消息
            } else {
    
    
                Toast.makeText(MainActivity.this, "时间到！游戏结束！", Toast.LENGTH_SHORT).show();         //提示时间已到
            }
        }
    };

}

Message

Used in cooperation with Handler, Looperas a data carrier.

Message contains several basic attributes: int arg1,arg2, Object obj, Messenger replyTo, what, and these attributes can be used to store information without allocating new storage space.

• Obtaining Message objects: Through the following two methods, you can avoid allocating new objects and obtain objects from the global pool.
  • Message.obtain()
  • Handler.obtainMessage()

Looper

It is used to continuously pass the message loop to the Handler for the thread to process.

The basic steps:

Example:

class LooperThread extends Thread {
    
    
      public Handler mHandler;

      public void run() {
    
    
          Looper.prepare();// 1. 初始化Looper

          mHandler = new Handler(Looper.myLooper()) {
    
    
              public void handleMessage(Message msg) {
    
    
                  // process incoming messages here
              }
          };// 创建Handler

          Looper.loop();// d
      }
  }