UIViewController类别不适用于viewDidLoad

Question

I'm using a custom rootViewController, and am using the code below to access it from any UIViewController

@implementation UIViewController(CustomRootVC)

- (CustomRootVC*)customViewController
{
  UIViewController *parent = self;
  Class customClass = [CustomRootVC class];

  while ( nil != (parent = [parent parentViewController]) && ![parent customClass] )
  {
  }

  return (id)parent;
}

@end

If I call self.customViewController on viewDidLoad I get nil. If I call it on willAppear I get the reference I expect.

I'm guessing this is something to do with the order I add the view controllers to my view controller container (ie viewDidLoad is called before the view controller has been added to customViewController and so it isn't a parent), but I can't spot anything obvious. I add the view controllers as follows:

- (void)addViewController:(UIViewController*)controller toWrapper:(PLSliderView*)wrapper{
  [self addChildViewController:controller];
  [self addView:controller.view ToWrapper:wrapper];
  [self.viewControllers addObject:controller];
  [controller didMoveToParentViewController:self];
}

In particular, the issue seems to be with adding a new view controller and view as follows:

- (void)replaceTopOfStackWithViewController:(UIViewController *)newController animated:  (BOOL)animated {
  UIViewController *oldController = self.currentController;
  [self addChildViewController:newController];
  [self transitionFromViewController:oldController
                toViewController:newController
                        duration:1.0
                         options:UIViewAnimationOptionTransitionCrossDissolve
                      animations:nil
                      completion:^(BOOL finished) {                                    
                        [self.rightViewController didMoveToParentViewController:self];
                        [self removeViewController:oldController];
                        [self queryDimensions:@"REPLACE"];
                        [self.view setUserInteractionEnabled:YES];
                        self.currentController = newController
                      }];

}

Answer 1

this piece of code (parent = [parent parentViewController]) sets parent equal to self.parentViewController . If self does not have a parent view controller at the time this is called, it would return nil as expected.

more broadly, I'm not sure what you're trying to accomplish with this code, or why you need to use a category. it seems like that sort of behavior would make more sense in a UIViewController subclass.

Answer 2

在调用viewDidLoad时，尚未将视图控制器添加到视图控制器层次结构中，因此它没有父视图控制器，因此您的函数按预期返回nil。