iOS Swift 只有 运行 应用程序的主线程错误

Question

我是 swift 的新手，我有一个登录页面，它获取用户凭据并检查它是否是正确的凭据。我认为 return JSON 中的响应如果它是正确的凭据，那么我会尝试转到新的 ViewController 。当我尝试转到新的视图控制器时出现此错误，我关闭它，所以我不知道为什么会遇到这个问题。这是我的代码

func LoginClosure(completion:@escaping (Bool) ->Void) {
    var check = 0
    let url:URL = URL(string:ConnectionString+"login")!

    if submitEmail == nil || submitPassword == nil {
        submitEmail = email.text!
        submitPassword = password.text!
    }

    let session = URLSession.shared
    var request = URLRequest(url: url)
    request.httpMethod = "POST"
    let parameter = "Email=\(submitEmail!)&password=\(submitPassword!)"
    request.httpBody = parameter.data(using: String.Encoding.utf8)
    DispatchQueue.main.async {
        session.dataTask(with:request, completionHandler: { (data, response, error) in
            if error != nil {
                // print(error)
            } else {
                do {
                    let parsedData = try JSONSerialization.jsonObject(with: data!, options: .allowFragments) as? [String:Any]

                    if let Streams = parsedData?["Profile"] as? [AnyObject]  {
                        // check for misspelled words
                        for Stream in Streams {
                            if let rr = Stream["result"] as? Bool {
                                self.result = rr
                            } else {
                                self.result = true
                            }

                            if let id = Stream["id"] as? Int {
                                self.defaults.setValue(id, forKey: "my_id")
                                // Success
                                MYID = id
                                completion(true)
                                return
                            }
                        }

                        if check == 0 {
                            // Bad credentials
                            completion(false)
                        }
                    }
                } catch let error as NSError {
                    print(error)
                }
            }
        }).resume()
    }
}

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Only run on the main thread!'

此行出现该错误：

let next = self.storyboard?.instantiateViewController(withIdentifier: "AccountC") as! AccountC
self.present(next, animated: true, completion: nil)

Answer 1

As per apple standards, you have to perform UI activity in the main queue only.

只需在 main queue 中调用您的闭包，如下所示。

DispatchQueue.main.async {
    completion(true)
}

您也可以在 main queue 中仅执行 UI 更改，如下所示。

DispatchQueue.main.async {
    let next = self.storyboard?.instantiateViewController(withIdentifier: "AccountC") as! AccountC
    self.present(next, animated: true, completion: nil)
}

@rmaddy 感谢您的宝贵建议。

Answer 2

在你的代码中，我看到你在主队列中发起了网络调用。这确保了数据任务的创建和启动将在主线程上执行。但它不保证完成闭包也会在主线程上被调用。

因此我建议从 DispatchQueue.main.async 块中删除网络调用。然后请在DispatchQueue.main.async block中执行执行UI更新的代码如下。

DispatchQueue.main.async {    
    let next = self.storyboard?.instantiateViewController(withIdentifier: "AccountC") as! AccountC
    self.present(next, animated: true, completion: nil)
}