ios - 将 JSON 数据导出到文本字段时出现问题

Question

我正在使用 JSONDecoder 协议(protocol)从数据库获取一些数据。

以下代码的所有内容均按预期工作，但我无法将 car.driver_name 导出到名为 contacttextField 的文本字段

我尝试设置 self.contacttextField = car.driver_name 但结果不佳。由于某种原因，解码后的 JSON 中的文本大约需要一分钟才能显示出来，调试器会显示:

10  Foundation                          0x00000001d67a8908 <redacted> + 740
11  Foundation                          0x00000001d689ecec <redacted> + 272
12  libdispatch.dylib                   0x0000000102a436f0 _dispatch_call_block_and_release + 24
13  libdispatch.dylib                   0x0000000102a44c74 _dispatch_client_callout + 16
14  libdispatch.dylib                   0x0000000102a47ffc _dispatch_continuation_pop + 524
15  libdispatch.dylib                   0x0000000102a47458 _dispatch_async_redirect_invoke + 628
16  libdispatch.dylib                   0x0000000102a55dc8 _dispatch_root_queue_drain + 372
17  libdispatch.dylib                   0x0000000102a567ac _dispatch_worker_thread2 + 156
18  libsystem_pthread.dylib             0x00000001d5a591b4 _pthread_wqthread + 464
19  libsystem_pthread.dylib             0x00000001d5a5bcd4 start_wqthread + 4

以下是我正在使用的代码:

struct FacilityInfo: Decodable {
    let driver_name: String
}

class infoViewController: UIViewController {
    @IBOutlet weak var usernameTextField: UITextField!

    override func viewDidLoad() {
        super.viewDidLoad()

        let url = URL(string: "https://example.com/example/test.php")!

        let task = URLSession.shared.dataTask(with: url) { data, response, error in
            // ensure there is no error for this HTTP response
            guard error == nil else {
                print ("error: \(error!)")
                return
            }

            // ensure there is data returned from this HTTP response
            guard let data = data else {
                print("No data")
                return
            }

            // Parse JSON into array of Car struct using JSONDecoder

            guard let cars = try? JSONDecoder().decode([FacilityInfo].self, from: data) else {
                print("Error: Couldn't decode data into cars array")
                return
            }

            for car in cars {
                print("car name is \(car.driver_name)")
                self.usernameTextField.text = cars.driver_name
            }
        }

        task.resume()

Answer 1

URLSession.dataTask 在后台线程上执行其闭包，但所有 UI 更新都需要从主线程进行。因此，您需要在主线程上执行对 usernameTextField.text 的调用。

...
guard let cars = try? JSONDecoder().decode([FacilityInfo].self, from: data), let firstCar = cars.first else {
    print("Error: Couldn't decode data into cars array")
    return
}
DispatchQueue.main.async {
    self.usernameTextField.text = firstCar.driver_name
}

另请记住，cars 是一个数组，因此您应该访问其元素之一，该元素具有 driver_name 属性，并将其分配给文本字段的 文本 属性。例如，我已分配第一个元素的值，但可以更改该值以满足您的要求。

您还应该遵守 Swift 命名约定，即变量名称采用小驼峰命名法 (driverName)。