ios - 检查后是否仍显示“在演示时尝试演示”？

 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，但可以多次调用此代码。我已经添加了此支票：

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

但这似乎并不能阻止这个错误：

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

最佳答案

您的guard不是有效支票。isBeingPresented正在一个全新的视图控制器实例上调用，该实例尚未呈现。因此isBeingPresented将始终是false。此外，该属性只能在视图控制器的view[Will|Did]Appear方法中使用。
您要检查的是tabBarController是否已经提供了另一个视图控制器。
最后，只创建和设置登录视图控制器（如果应该显示）。

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)
    }
}

关于ios - 检查后是否仍显示“在演示时尝试演示”？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/44222543/