再按一次后退键退出应用程序

long lastTouchBackTime = 0L;
long nowTime = 0L;
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
if (keyCode == KeyEvent.KEYCODE_BACK) {
nowTime = System.currentTimeMillis();
if (nowTime - lastTouchBackTime >= 2000) {
AndroidUtils.showAlertDialog("再按一次后退键退出应用程序", this);
lastTouchBackTime = nowTime;
} else {
finish();
System.exit(0);
}
}
return false;
}