Question

我正在使用我的SignUpViewController创建一个帐户，当用户使用不符合密码规范的密码注册一个帐户时，该程序应发出警报。出于某种原因，我不断得到：

由于未捕获的异常'NSInternalInconsistencyException'而终止应用程序，原因：'-[UIKeyboardTaskQueue waitUntilAllTasksAreFinished]只能从主线程调用。'

如何返回主线程，以便程序仅发出警报？

这是该视图控制器的代码：

@IBAction func signupPressed(_ sender: Any) {
     // Get a reference to the user pool
    let userPool = AppDelegate.defaultUserPool()
    // Collect all of the attributes that should be included in the signup call
        let emailAttribute = AWSCognitoIdentityUserAttributeType(name: "email", value: self.email.text!)
        let firstNameAttribute = AWSCognitoIdentityUserAttributeType(name: "given_name", value: self.firstName.text!)
        let lastNameAttribute = AWSCognitoIdentityUserAttributeType(name: "family_name", value: self.lastName.text!)
        let birthdayAttribute = AWSCognitoIdentityUserAttributeType(name: "birthdate", value: self.birthday.text!)
    // Actually make the signup call passing in those attributes

        userPool.signUp(UUID().uuidString, password: self.password.text!, userAttributes: [emailAttribute, firstNameAttribute, lastNameAttribute, birthdayAttribute], validationData: nil)
        .continueWith { (response) -> Any? in
            if response.error != nil {
                // Error in the signup process
                let alert = UIAlertController(title: "Error", message: response.error?.localizedDescription, preferredStyle: .alert)
                alert.addAction(UIAlertAction(title: "OK", style: .default, handler:nil))
                self.present(alert, animated: true, completion: nil)
            } else {
                self.user = response.result!.user
                // Does user need verification?
                if (response.result?.userConfirmed?.intValue != AWSCognitoIdentityUserStatus.confirmed.rawValue) {
                    // User needs confirmation, so we need to proceed to the verify view controller
                    DispatchQueue.main.async {
                        self.performSegue(withIdentifier: "VerifySegue", sender: self)
                    }
                } else {
                    // User signed up but does not need verification
                    DispatchQueue.main.async {
                        self.presentingViewController?.dismiss(animated: true, completion: nil)
                    }
                }
            }
            return nil
    }
}

Answer 1

这也是主线程工作

DispatchQueue.main.async { 
    let alert = UIAlertController(title: "Error", message: response.error?.localizedDescription, preferredStyle: .alert)
    alert.addAction(UIAlertAction(title: "OK", style: .default, handler:nil))
    self.present(alert, animated: true, completion: nil)
}

如果所有事情都需要在main中完成，那么您只能用1 DispatchQueue.main.async包围响应

Answer 2

在闭包中，如果错误不是nil，您是否可以像下面那样更新代码并重试：

if response.error != nil {
            // Error in the signup process

            DispatchQueue.main.async {
                let alert = UIAlertController(title: "Error", message: response.error?.localizedDescription, preferredStyle: .alert)
                alert.addAction(UIAlertAction(title: "OK", style: .default, handler:nil))
                self.present(alert, animated: true, completion: nil)    
            }
        }

Answer 3

只写

self.present(alert, animated: true, completion: nil)

在Dispatch.main.async内部，就像您对其他脚本所做的一样

DispatchQueue.main.async {
                        self.present(alert, animated: true, completion: nil)
                    }

Answer 4

您已经在整理视图控制器并使用DispatchQueue.main.async执行segue。您还应该执行此操作以显示UIAlertController。您最好将整个方法主体编组到主线程。

Answer 5

与DispatchQueue.main.async一起，我们可以添加[weak self]支票以避免保留周期，例如

DispatchQueue.main.async { [weak self] in
    self?.present(alert, animated: true, completion: nil)
}

如何在Xcode中重新回到主线程？

5 个答案: