ios - 执行某些说明后无法从一个 View 转到另一个 View

Question

我的应用程序的一部分有这个实现:

为什么当我点击“cerca per ISBN”按钮时，它会转到 tableView，而不执行我编写的说明？

这是我点击的“cerca per ISBN”按钮的代码:

@IBAction func ISBNButtonClick(_ sender: Any) {

    let libro = Libro.text! as String

    if Libro.text!.isEmpty  {

        //Alert per segnalare i campi mancanti, oltre a caselle rosse

        var myAlert = UIAlertController(title:"Attenzione\n", message:"Inserire il codice ISBN", preferredStyle:UIAlertControllerStyle.alert);

        let okAction = UIAlertAction(title:"Ok", style:UIAlertActionStyle.default){ action in }

        myAlert.addAction(okAction);
        self.present(myAlert, animated:true, completion:nil);

        // placeholder rosso se la text è vuota

        Libro.attributedPlaceholder = NSAttributedString(string:"Digita qui...", attributes: [NSForegroundColorAttributeName: UIColor.red])

        //se tutti i campi obbligatori sono stati inseriti, proseguo ad altri controlli
    }else{
        if(isNumeric(string: libro)){
            if((libro.characters.count) < 13 || (libro.characters.count) > 13){

                //Alert per segnalare l'ISBN più corto di 13 numeri

                var myAlert = UIAlertController(title:"Attenzione\n", message:"L'ISBN deve essere di 13 cifre", preferredStyle:UIAlertControllerStyle.alert);

                let okAction = UIAlertAction(title:"Ok", style:UIAlertActionStyle.default){ action in }

                myAlert.addAction(okAction);
                self.present(myAlert, animated:true, completion:nil);
            }else{
                //inviare dati al server
                let myUrl = NSURL(string:"http://chuadiv.ddns.net/easytoschool/fetch_book_detailed.php");

                let request = NSMutableURLRequest(url:myUrl as! URL);
                request.httpMethod = "POST";
                let postString = "name=\(libro)&mail=\(UserDefaults.standard.object(forKey: "userEmail") as? String)";
                request.httpBody = postString.data(using: String.Encoding.utf8);

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

                    if error != nil{
                        print("error=\(error)")
                        return
                    }

                    var err: NSError?

                    do{
                        var json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? NSArray


                        if let parseJSON: NSArray = json{

                            for index in 0...parseJSON.count-1 {

                                print("ciao")
                                let libro = parseJSON[index] as! [String:Any]
                                print("\n\n",index,":\n")

                                let book = resultCell.init(bookId: libro["id"] as! String,bookName: libro["name"] as! String,bookAuthor: libro["author"] as! String,bookSchool: libro["school"] as! String,bookPrice: libro["price"] as! String,bookStatus: libro["status"] as! String,bookISBN: libro["isbn"] as! String,bookType: libro["type"] as! String,bookIdSeller: libro["idSeller"] as! String,bookNameSeller: libro["nameSeller"] as! String,bookSurnameSeller: libro["surnameSeller"] as! String)

                                book.printBook();

                                HomeViewController.booksArray.append(book)
                            }

                        }
                    }catch{
                        print("error=\(error)")
                        return
                    }
                }
                task.resume();

                performSegue(withIdentifier: "homeToListBook", sender: self)

            }
        }else{
            var myAlert = UIAlertController(title:"Attenzione\n", message:"Inserire solo numeri per la ricerca attraverso codice ISBN", preferredStyle:UIAlertControllerStyle.alert);

            let okAction = UIAlertAction(title:"Ok", style:UIAlertActionStyle.default){ action in }

            myAlert.addAction(okAction);
            self.present(myAlert, animated:true, completion:nil);
        }
    }
}

我希望当我按下按钮时它会设置我的数组并在它进入 tableView 后，但我不能

Answer 1

问题是 dataTask 的完成 block 将调用 async，因此它将稍后调用，并且您当前正在其完成 block 之外执行 segue。因此，您需要做的是在 Main 线程上的 dataTask 完成 block 内调用 performSegue 。还可以使用 URL 和 URLRequest 而不是 NSURL 和 NS(Mutable)URLRequest

let myUrl = URL(string:"http://chuadiv.ddns.net/easytoschool/fetch_book_detailed.php")

let request = URLRequest(url:myUrl!)
request.httpMethod = "POST";
let postString = "name=\(libro)&mail=\(UserDefaults.standard.string(forKey: "userEmail")!)"
request.httpBody = postString.data(using: .utf8)
let task = URLSession.shared.dataTask(with: request as URLRequest){
    data, response, error in

    if error != nil{
        print("error=\(error)")
        return
    }

    var err: NSError?

    do{
        var json = try JSONSerialization.jsonObject(with: data!, options: .mutableContainers) as? [[String:Any]]


        if let parseJSON = json {                
            for libro in in parseJSON {                                        
                let book = resultCell.init(bookId: libro["id"] as! String,bookName: libro["name"] as! String,bookAuthor: libro["author"] as! String,bookSchool: libro["school"] as! String,bookPrice: libro["price"] as! String,bookStatus: libro["status"] as! String,bookISBN: libro["isbn"] as! String,bookType: libro["type"] as! String,bookIdSeller: libro["idSeller"] as! String,bookNameSeller: libro["nameSeller"] as! String,bookSurnameSeller: libro["surnameSeller"] as! String)

                book.printBook();

                HomeViewController.booksArray.append(book)
            }

            //Perform segue now
            DispatchQueue.main.async {
                performSegue(withIdentifier: "homeToListBook", sender: self)
            }                
        }
    }catch{
        print("error=\(error)")
        return
    }
}
task.resume()

注意:在 Swift 中使用 Swift native 类型数组和字典，而不是 NSArray 和 NSDictionary。