检查后仍然出现“尝试在已经呈现时呈现”？

Posted 2023-03-12

【中文标题】检查后仍然出现“尝试在已经呈现时呈现”？

【英文标题】："Attempt to present while already presenting" still appearing after checks?

【发布时间】：2017-05-27 23:44:08

【问题描述】：

 let appDelegate = UIKit.UIApplication.shared.delegate!

        if let tabBarController = appDelegate.window??.rootViewController as? UITabBarController 
            let storyboard = UIStoryboard.init(name: "Main", bundle: nil)
            let signInVC   = storyboard.instantiateViewController(withIdentifier: "SignInVC") as! SignInVC

            guard !signInVC.isBeingPresented else 
                log.warning("Attempt to present sign in sheet when it is already showing")
                return
            

            signInVC.modalPresentationStyle = UIModalPresentationStyle.formSheet

            tabBarController.present(signInVC, animated: true, completion: nil)
        

尽管出现了signInVC，但此代码可以多次调用。我已经添加了这个检查：

 guard !signInVC.isBeingPresented else 
     log.warning("Attempt to present sign in sheet when it is already showing")
     return
 

但它似乎并没有阻止这个错误：

Warning: Attempt to present <App.SignInVC: 0x101f2f280>  on <UITabBarController: 0x101e05880> which is already presenting <App.SignInVC: 0x101f4e4c0>

【参考方案1】：

您的guard 不是有效支票。 isBeingPresented 正在一个尚未呈现的全新视图控制器实例上被调用。所以isBeingPresented 永远是false。除此之外，该属性只能在视图控制器的 view[Will|Did]Appear 方法中使用。

你要检查的是tabBarController是否已经呈现了另一个视图控制器。

最后，只有在应该显示的情况下才创建和设置登录视图控制器。

let appDelegate = UIKit.UIApplication.shared.delegate!

if let tabBarController = appDelegate.window?.rootViewController as? UITabBarController 
    if tabBarController.presentedViewController == nil 
        let storyboard = UIStoryboard.init(name: "Main", bundle: nil)
        let signInVC   = storyboard.instantiateViewController(withIdentifier: "SignInVC") as! SignInVC
        signInVC.modalPresentationStyle = UIModalPresentationStyle.formSheet

        tabBarController.present(signInVC, animated: true, completion: nil)
    

【讨论】：

这是否解决了您的问题或者您仍有问题？