Handler实践三种效果之倒计时的实现代码

代码如下：

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

import java.lang.ref.WeakReference;

public class MainActivity extends AppCompatActivity {

/**
 * 倒计时标记handle code
 */
public  static  final  int COUNTDOWN_TIME_CODE = 100001;
/**
 * 倒计时间隔
 */
public  static  final  int  DELAY_MILLIS = 1000;
/**
 * 倒计时最大值
 */
public  static  final  int  MAX_COUNT = 10;


private TextView mCountdownTimeTextView;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //得到控件
    mCountdownTimeTextView= (TextView)findViewById(R.id.countdownTimeTextView);

    //创建了一个handler
    //这个handler是静态的不会发生内存泄漏，因为我们传入的activity是弱引用，引用完就就会回收掉，
    
    CountdownTimeHandler handler = new CountdownTimeHandler(this);

    //新建了一个message
    Message message = Message.obtain();
    message.what = COUNTDOWN_TIME_CODE;
    message.arg1 = MAX_COUNT;

    //第一次发送这个message
    handler.sendMessageDelayed(message,DELAY_MILLIS);

}

public  static  class  CountdownTimeHandler extends Handler{
      static  final  int  MIN_COUNT = 0;
    final WeakReference<MainActivity> mWeakReference;

     CountdownTimeHandler(MainActivity activity){
        mWeakReference = new WeakReference<> (activity );
    }

    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);
        //获取当前activity的
        MainActivity activity =mWeakReference.get();

        switch (msg.what){
            case COUNTDOWN_TIME_CODE:
                int value = msg.arg1;
                activity.mCountdownTimeTextView.setText(String.valueOf(value --));

                 //循环发的消息控制
                if (value >= MIN_COUNT) {
                    Message message = Message.obtain();
                    message.what = COUNTDOWN_TIME_CODE;
                    message.arg1 = value;
                    sendMessageDelayed(message, DELAY_MILLIS);
                }

                break;
        }
    }
}
}