handler的使用如何实现Android计时与倒计时的几种方法

方法一

Timer与TimerTask（Java实现）

public class timerTask extends Activity{

    private int recLen = 11;
    private TextView txtView;
    Timer timer = new Timer();

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);

        setContentView(R.layout.timertask);
        txtView = (TextView)findViewById(R.id.txttime);

        timer.schedule(task, 1000, 1000);       // timeTask
    }

    TimerTask task = new TimerTask() {
        @Override
        public void run() {

            runOnUiThread(new Runnable() {      // UI thread
                @Override
                public void run() {
                    recLen--;
                    txtView.setText(""+recLen);
                    if(recLen < 0){
                        timer.cancel();
                        txtView.setVisibility(View.GONE);
                    }
                }
            });
        }
    };
}

方法二

TimerTask与Handler（不用Timer的改进型）

public class timerTask extends Activity{
    private int recLen = 11;
    private TextView txtView;
    Timer timer = new Timer();

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);

        setContentView(R.layout.timertask);
        txtView = (TextView)findViewById(R.id.txttime);

        timer.schedule(task, 1000, 1000);       // timeTask
    }

    final Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg){
            switch (msg.what) {
            case 1:
                txtView.setText(""+recLen);
                if(recLen < 0){
                    timer.cancel();
                    txtView.setVisibility(View.GONE);
                }
            }
        }
    };

    TimerTask task = new TimerTask() {
        @Override
        public void run() {
            recLen--;
            Message message = new Message();
            message.what = 1;
            handler.sendMessage(message);
        }
    };
}

方法三

Handler与Message（不用TimerTask）

public class timerTask extends Activity{
    private int recLen = 11;
    private TextView txtView;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.timertask);
        txtView = (TextView)findViewById(R.id.txttime);

        Message message = handler.obtainMessage(1);     // Message
        handler.sendMessageDelayed(message, 1000);
    }

    final Handler handler = new Handler(){

        public void handleMessage(Message msg){         // handle message
            switch (msg.what) {
            case 1:
                recLen--;
                txtView.setText("" + recLen);

                if(recLen > 0){
                    Message message = handler.obtainMessage(1);
                    handler.sendMessageDelayed(message, 1000);      // send message
                }else{
                    txtView.setVisibility(View.GONE);
                }
            }

            super.handleMessage(msg);
        }
    };
}

方法四

Handler与Thread（不占用UI线程）

public class timerTask extends Activity{
    private int recLen = 0;
    private TextView txtView;

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);

        setContentView(R.layout.timertask);
        txtView = (TextView)findViewById(R.id.txttime);

        new Thread(new MyThread()).start();         // start thread
    }

    final Handler handler = new Handler(){          // handle
        public void handleMessage(Message msg){
            switch (msg.what) {
            case 1:
                recLen++;
                txtView.setText("" + recLen);
            }
            super.handleMessage(msg);
        }
    };

    public class MyThread implements Runnable{      // thread
        @Override
        public void run(){
            while(true){
                try{
                    Thread.sleep(1000);     // sleep 1000ms
                    Message message = new Message();
                    message.what = 1;
                    handler.sendMessage(message);
                }catch (Exception e) {
                }
            }
        }
    }
}

方法五

Handler与Runnable（最简单型）

public class timerTask extends Activity{
    private int recLen = 0;
    private TextView txtView;

    public void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);

        setContentView(R.layout.timertask);
        txtView = (TextView)findViewById(R.id.txttime);

        handler.postDelayed(runnable, 1000);
    }

    Handler handler = new Handler();
    Runnable runnable = new Runnable() {
        @Override
        public void run() {
            recLen++;
            txtView.setText("" + recLen);
            handler.postDelayed(this, 1000);
        }
    };
}

计时与倒计时

方法1，方法2和方法3，都是倒计时

方法4，方法5，都是计时

计时和倒计时，都可使用上述方法实现（代码稍加改动）

UI线程比较

方法1，方法2和方法3，都是在UI线程实现的计时；

方法4和方法5，是另开Runnable线程实现计时

实现方式比较

方法1，采用的是Java实现，即Timer和TimerTask方式；

其它四种方法，都采用了Handler消息处理

推荐使用

如果对UI线程交互要求不很高，可以选择方法2和方法3

如果考虑到UI线程阻塞，严重影响到用户体验，推荐使用方法4，另起线程单独用于计时和其它的逻辑处理

方法5，综合了前几种方法的优点，是最简的