Swift 如果执行嵌套异步调用，函数将运行两次，否则将运行一次。需要帮助预先确定何时会发生这种情况

func-handleGetAllPhotoURLs从下面的一行调用，我已经确认代码行只在有断点的情况下执行一次

_ = FlickrClient.getAllPhotoURLs(currentPin: self.currentPin, fetchCount: fetchCount, completion: self.handleGetAllPhotoURLs(pin:urls:error:))

根据我的print语句的输出，该函数运行两次，因为如果url.count非零，它将打印两行输出。但是，如果urls.count为零，那么我只得到一条声明“urls.count-->0”的打印语句

handleGetAllPhotoURLs-->urls.count-->0//始终打印此行

handleGetAllPhotoURLs-->urls.count-->21//仅当URL参数不为空时才打印此行

func handleGetAllPhotoURLs(pin: Pin, urls: [URL], error: Error?){
    print("handleGetAllPhotoURLs ---> urls.count  ---> \(urls.count)")

    let backgroundContext: NSManagedObjectContext! = dataController.backGroundContext
    if let error = error {
        print("func mapView(_ mapView: MKMapView, didSelect... \n\(error)")
        return
    }

    let pinId = pin.objectID
    backgroundContext.perform {
        let backgroundPin = backgroundContext.object(with: pinId) as! Pin
        backgroundPin.urlCount = Int32(urls.count)
        try? backgroundContext.save()
    }

    for (index, currentURL) in urls.enumerated() {
        URLSession.shared.dataTask(with: currentURL, completionHandler: { (imageData, response, error) in
            guard let imageData = imageData else {return}
            connectPhotoAndPin(dataController: self.dataController, currentPin:  pin , data: imageData, urlString: currentURL.absoluteString, index: index)
        }).resume()
    }
}

此外，我有一个UILabel，它只在URL.count为零时显示自己，我只想在URL为空时显示它

现在，如果URL不是空的，应用程序会很快刷新空消息标签。这对我来说很有意义，因为print语句显示URL数组暂时为空

当URL.count为非零时，是否有办法避免向用户闪烁空消息UILabel

编辑：根据请求在下面添加代码。调用下面的函数以在完成处理程序中获取[URL]。然后将完成处理程序输入到： func handleGetAllPhotoURLs（pin:pin，URL:[URL]，错误：错误？

---

在

do

块中，调用

completion

两次。请看更正

do {
    let temp = try JSONDecoder().decode(PhotosSearch.self, from: dataObject)
    if temp.photos.photo.isEmpty == false {
       temp.photos.photo.forEach{
        let tempDict = [$0.id : $0.secret]
        array_photoID_secret.append(tempDict)

        let photoURL = FlickrClient.Endpoints.getOnePicture($0.id, $0.secret)
        let photoURLString = photoURL.toString
        array_URLString.append(photoURLString)

        getPhotoURL(photoID: $0.id, secret: $0.secret, completion: { (urlString, error) in
            guard let urlString = urlString else {return}
            array_URLString2.append(urlString)
            array_photo_URLs.append(URL(string: urlString)!)
            count = count + 1
            if count == temp.photos.photo.count {
                completion(currentPin, array_photo_URLs, nil)
            }
        })
      }
    } else {
        completion(currentPin, [], nil)
    }
    return
}

---

函数的内容不影响函数被调用的次数。我们必须看看你是如何调用这个方法的。进行编辑，希望能提供更多信息。类func getAllPhotoURLs（）返回一个完成处理程序，该处理程序随后进入func handleGetAllPhotoURLs（）。如果还有什么我能帮忙的，请告诉我。非常感谢。我找错地方了。我不知道我回来了两次。

do {
    let temp = try JSONDecoder().decode(PhotosSearch.self, from: dataObject)
    if temp.photos.photo.isEmpty == false {
       temp.photos.photo.forEach{
        let tempDict = [$0.id : $0.secret]
        array_photoID_secret.append(tempDict)

        let photoURL = FlickrClient.Endpoints.getOnePicture($0.id, $0.secret)
        let photoURLString = photoURL.toString
        array_URLString.append(photoURLString)

        getPhotoURL(photoID: $0.id, secret: $0.secret, completion: { (urlString, error) in
            guard let urlString = urlString else {return}
            array_URLString2.append(urlString)
            array_photo_URLs.append(URL(string: urlString)!)
            count = count + 1
            if count == temp.photos.photo.count {
                completion(currentPin, array_photo_URLs, nil)
            }
        })
      }
    } else {
        completion(currentPin, [], nil)
    }
    return
}