【ios】收到系统内存警告时，应如何释放内存

- (void)didReceiveMemoryWarning
{
    [super didReceiveMemoryWarning];

    if (_userInfoViewCtl != nil && [_userInfoViewCtl isViewLoaded]) {
        if (_userInfoViewCtl.view.window == nil) {
            self.userInfoViewCtl = nil;
        }
    }
}

-(KEUserInfoViewController *) userInfoViewCtl
{
    if (!_userInfoViewCtl) {
        _userInfoViewCtl = [[KEUserInfoViewController alloc] init];
    }
    return _userInfoViewCtl;
}