LargeTitles UIScrollView does not support multiple observers implementing _scrollViewWillEndDraggingWithVelocity:targetContentOffset

问题:

I have implemented large titles in my app with the following code:

if #available(iOS 11.0, *) {             navigationController?.navigationBar.prefersLargeTitles = true             navigationItem.largeTitleDisplayMode = .always         } else {             // Fallback on earlier versions         } }  func scrollViewDidScroll(_ scrollView: UIScrollView) {     if scrollView.contentOffset.y <= 0 {         if #available(iOS 11.0, *) {             self.navigationItem.largeTitleDisplayMode = .always         } else {             // Fallback on earlier versions         }     } else {         if #available(iOS 11.0, *) {             self.navigationItem.largeTitleDisplayMode = .never         } else {             // Fallback on earlier versions         }     }     self.navigationController?.navigationBar.setNeedsLayout()     self.view.setNeedsLayout()     UIView.animate(withDuration: 0.01, animations: {         self.navigationController?.navigationBar.layoutIfNeeded()         self.view.layoutIfNeeded()     }) } 

I am able to successfully toggle between views on a tabbar but when I push a view ontop of the tabbar controller and then pop it off using this code:

_ = self.navigationController?.popViewController(animated: true) 

I get this crash when I toggle between views on the tabbar again: Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'ERROR: UIScrollView does not support multiple observers implementing _scrollViewWillEndDraggingWithVelocity:targetContentOffset:'

回答1:

I've the same problem and I fixed it by removing this line from AppDelegate:

UINavigationBar.appearance().prefersLargeTitles = true 

and handle prefersLargeTitles inside viewDidLoad in certain UIViewController

回答2:

The problem happened when the tableview was still scrolling when I went to another view. I fixed the problem by setting a bool in the scrollViewDidScroll that disables any scrolling when the segue is started.

    func scrollViewDidScroll(_ scrollView: UIScrollView) {         if viewIsVisible {             if scrollView.contentOffset.y <= 0 {                 if #available(iOS 11.0, *) {                     self.navigationItem.largeTitleDisplayMode = .always                 } else {                     // Fallback on earlier versions                 }             } else {                 if #available(iOS 11.0, *) {                     self.navigationItem.largeTitleDisplayMode = .never                 } else {                     // Fallback on earlier versions                 }             }             self.navigationController?.navigationBar.setNeedsLayout()             self.view.setNeedsLayout()             UIView.animate(withDuration: 0.01, animations: {                 self.navigationController?.navigationBar.layoutIfNeeded()                 self.view.layoutIfNeeded()             })         }     }      override func prepare(for segue: UIStoryboardSegue, sender: Any?) {         self.viewIsVisible = false } 

文章来源: LargeTitles UIScrollView does not support multiple observers implementing _scrollViewWillEndDraggingWithVelocity:targetContentOffset