Android 通信机制Message、Handler 的用法

Android中提供了通信机制，Message、Handler 等，Message用于在子线程中传递数据，Handler用于发送数据到主线程中，

下面介绍基于Message、Handler的计时器

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

public class TimeActivity extends AppCompatActivity {
    private TextView tv;                //布局中用于显示计时数字
    private Button time;               //布局中设置Button，用于开始计时
    private int a=100;
    private Handler handler =new Handler(){
        @Override
        public void handleMessage(Message msg) {
            super.handleMessage(msg);
            tv.setText(srt+msg.what + "");
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_time);
        tv= (TextView) findViewById(R.id.tv);
        time= (Button) findViewById(R.id.time);
        tv.setText("100");
        time.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                new Thread(new time()).start();  //调用time类

            }
        });

    }

     public class time implements Runnable{

        @Override
        public void run() {
            int i=100;
            while(i>=0){
                try {
                  Thread.sleep(200);                //延时0.5秒
                } catch (InterruptedException e) {
                  e.printStackTrace();
                }
                  i--;
                  handler.sendEmptyMessage(i);   //Handler方法
             }
           }
      }
}