点击两次back键后再退出程序，既简单又好用
点击两次back后再退出程序，有时候会对用户体验有好处，下面是一种十分简单的方法
12345678910111213
private long exitTime = 0;@Overridepublic boolean onKeyDown(int keyCode, KeyEvent event) { ExitApp(); return false;}public void ExitApp() { if ((System.currentTimeMillis() - exitTime) > 2000) { Toast.makeText(BackAppActivity.this, "再按一次退出程序", Toast.LENGTH_SHORT).show(); exitTime = System.currentTimeMillis(); } else { finish( ......