Android倒计时的几种方式

方法一：使用Handler+Runnable

public class CountDownActivity extends AppCompatActivity {    private static final String TAG = "CountDownActivity";    @Override    protected void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.activity_count_down);        testCountDown();    }    private void testCountDown() {        Log.e(TAG, "testCountDown: start  currentTimeMillis = "+System.currentTimeMillis() );        countDownHandler.postDelayed(countDownRunnable,3000);    }    Handler countDownHandler = new Handler();    Runnable countDownRunnable = new Runnable() {        @Override        public void run() {            Toast.makeText(context,"时间到",Toast.LENGTH_LONG).show();            Log.e(TAG, "testCountDown: end  currentTimeMillis = "+System.currentTimeMillis() );        }    };    @Override    protected void onDestroy() {        super.onDestroy();        if(countDownHandler != null)        {            //移除回调，避免内存泄漏            countDownHandler.removeCallbacks(countDownRunnable);        }    }}

相差10毫秒左右

方法二： Timer+TimerTask

    private void testCountDown() {        final Timer timer = new Timer();        TimerTask timerTask = new TimerTask() {            @Override            public void run() {                Log.e(TAG, "testCountDown: end  currentTimeMillis = "+System.currentTimeMillis() );                Log.e(TAG, "run: "+Thread.currentThread() );                timer.cancel();//                Toast.makeText(context,"时间到",Toast.LENGTH_LONG).show(); //time线程不能改变UI//                startActivity(MainActivity.class);//不能更新UI，但是可以启动activity            }        };        Log.e(TAG, "testCountDown: start  currentTimeMillis = "+System.currentTimeMillis() );        timer.schedule(timerTask,3000);    }

`虽然相差0毫秒，但是Timer并不能保证准时执行任务的，需要看前面的任务有没有执行完。

方法三：CountDownTimer

    private void testCountDown(){        CountDownTimer countDownTimer = new CountDownTimer(3000,1000) {            @Override            public void onTick(long millisUntilFinished) {                Log.e(TAG, "onTick: "+ millisUntilFinished);            }            @Override            public void onFinish() {                Log.e(TAG, "onFinish: " );            }        };        countDownTimer.start();//        countDownTimer.cancel();    }

这个还不错

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