@SuppressLint("HandlerLeak")

    Handler handler = new Handler(){

        public void handleMessage(Message msg){

             switch (msg.what) {

             }

        }

    };

    boolean willExit = false;

    @Override

    public void onBackPressed() {

        // TODO Auto-generated method stub

        Runnable resetFlag = new Runnable() {

            @Override

            public void run() {

                // TODO Auto-generated method stub

                willExit = false;

            }

        };

        if(!willExit){

            Toast.makeText(this, "再按一次退出程序", Toast.LENGTH_SHORT).show();

            willExit = true;

            handler.postDelayed(resetFlag, 2*1000);

        }else{

            handler.removeCallbacks(resetFlag);

            finish();

        }

    }