iOS 创建VC时赋值大坑

需求是创建一个VC，创建后赋值参数，然后VC内部方法将利用此VC初始化时被赋值的全局变量作为参数进行网络请求，初始化如下：

1- (FlightDomesticFreeViewController *)freeDomesticFlightViewController
2{
3  if (_freeDomesticFlightViewController) {
4       return _freeDomesticFlightViewController;
5    }
6   _freeDomesticFlightViewController = [[TNBoss3FlightDomesticFreeViewController alloc] init];
7   _freeDomesticFlightViewController.adultNum = self.adultNum;
8   _freeDomesticFlightViewController.childNum = self.childNum;
9   _freeDomesticFlightViewController.currentSeqNum = 1;
10  _freeDomesticFlightViewController.baseSinglePriceArray = self.baseSinglePriceArray;
11  _freeDomesticFlightViewController.basePackagePrice = self.basePackagePrice;
12   _freeDomesticFlightViewController.productInfo = self.freeFlightInfoDict[PRODUCT_INFO];
13   _freeDomesticFlightViewController.selectedFlights = self.freeFlightInfoDict[SELECT_FLIGHT];
14    _freeDomesticFlightViewController.departureCityCode = self.freeFlightInfoDict[DEPARTURE_CITY_CODE];
15   _freeDomesticFlightViewController.backCityCode = self.freeFlightInfoDict[BACK_CITY_CODE];
16   _freeDomesticFlightViewController.queryFlight = self.queryFlight;
17   _freeDomesticFlightViewController.bookCity = self.bookCity;
18   _freeDomesticFlightViewController.delegate = self;
19   _freeDomesticFlightViewController.isChangeOrder = self.isChangeOrder;
20   _freeDomesticFlightViewController.view.frame = self.freeContentView.bounds;
21   _freeDomesticFlightViewController.journeyId = self.baseInfo.journeyId;
22   [_freeContentView addSubview:_freeDomesticFlightViewController.view];
    
23   [self addChildViewController:_freeDomesticFlightViewController];
24    return _freeDomesticFlightViewController;
}

然后测试告诉我入参没有journeyId这个字段，后来经过反复断点调试，发现20行执行完以后便会调入VC的内部方法，进行网络请求，而此时21行journeyId还未赋值，所以导致入参此字段为空。原因就是因为20行执行后，VC的viewDidLoad会执行，也就是开始执行VC的内部方法，故这种初始化属性方式不可在设置frame方法后，也就是将21行代码放在20行之前，便可避免这种低级错误。