Question

我有这段代码：

let task = session.dataTask(with: request as URLRequest, completionHandler: {
        (
        data, response, error) in

        guard let _:Data = data, let _:URLResponse = response  , error == nil else {
            print("error")
            return
        }

        let dataString = NSString(data: data!, encoding: String.Encoding.utf8.rawValue)
        result = dataString as? String ?? ""
        print("Data received is: " + result)

        if (result == "failed") {
            displayAlertMessage(userMessage: "Your credentials are incorrect. Please check your email and password.") //ERROR
            //ERROR ^
            print("Cannot login.")
        } else {

            // Store the userID for local use
            let userID = result
            UserDefaults.standard.set(userID, forKey:"userID")
            UserDefaults.standard.synchronize()

            // Since login is successful, proceed to Prime page
            DispatchQueue.main.async() {
                self.performSegue(withIdentifier: "goToPrimePage", sender: self)
            }
            print("Can login.")
        }
    })

错误一直告诉我要添加自己。到那个错误行。但在添加self后，程序崩溃并显示消息

由于未捕获的异常终止应用程序＆＃39; NSInternalInconsistencyException＆＃39;，原因：＆＃39; - [UIKeyboardTaskQueue waitUntilAllTasksAreFinished]只能从主线程调用。＆＃39;

我对swift很新，所以我可能不理解很多使用的术语。

Answer 1

添加self并确保在向用户显示任何警告消息之前跳回主线程。

DispatchQueue.main.async() {
    self.displayAlertMessage(userMessage: "Your credentials are incorrect. Please check your email and password.")
}

Answer 2

参考Rob对已删除解决方案的评论，但这有效：

DispatchQueue.main.async() {
    self.displayAlertMessage(userMessage: "Your credentials are incorrect. Please check your email and password.")
}

不知道如何或为什么，谢谢“弥迦”。

在闭包中调用方法需要明确的自我

2 个答案: