iOS视图层次结构，用于设置自动布局约束

Question

What is the closest ancestor to self.navigationController.navigationBar and a subview of self.view in a view controller so I can add the constraint to that ancestor?

self.searchBar = [[UISearchBar alloc] initWithFrame:CGRectZero];
[self.searchBar setTranslatesAutoresizingMaskIntoConstraints:NO];
[self.view addSubview:self.searchBar];

NSLayoutConstraint* cn = [NSLayoutConstraint constraintWithItem:self.searchBar  
attribute:NSLayoutAttributeTop relatedBy:NSLayoutRelationEqual 
toItem:self.navigationController.navigationBar attribute:NSLayoutAttributeBottom 
multiplier:1.0 constant:0];

I tried doing

[self.view addConstraint:cn];
[self.navigationController.view addConstraint:cn];

but both times I get the error, "Does the constraint reference something from outside the subtree of the view? That's illegal."

Can someone explain the view hierarchy of a view controller in relation to the navigationController?

Thanks!

Answer 1

The view tree looks like this:

So, navigationController.view is the closest ancestor of the navigation bar and your view. I'm not sure why that didn't work. Where did you put that code?