Android_Back键再按一次退出程序

主要思路：在Activity中覆写Activity的onKeyDown方法

    private long exitTime = 0;    public boolean onKeyDown(int keyCode, KeyEvent event) {        if (keyCode == KeyEvent.KEYCODE_BACK) {            if ((System.currentTimeMillis() - exitTime) > 2000) {                Toast.makeText(this,getResources().getString(R.string.tips_exit),0).show();;                exitTime = System.currentTimeMillis();            } else {                Intent intent = new Intent(Intent.ACTION_MAIN);                intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);                intent.addCategory(Intent.CATEGORY_HOME);                startActivity(intent);            }            return true;        }        return super.onKeyDown(keyCode, event);    }