Question

我必须使用以下代码从数据库中获取一堆图像，其中url是一个数组，具有指向Firebase存储上图像的链接。

func downloadFromServer(url: [String], imageNumber: Int){
    for i in url{
    let i = URL(string: i)
        print("I" , i)
        URLSession.shared.dataTask(with: i!) { data, response, error in
         guard
             let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200,
             let data = data, error == nil,
             let image = UIImage(data: data)

             else { return }
            print("Here", image)
         DispatchQueue.main.async() {
                print("Appended")
                imageArrayWatch.append(image)
                //imageArr.append(image)


         }
         }.resume()
    }

}

我希望我的应用程序在从数据库中获取图像时显示加载屏幕。但是，当我尝试像这样在视图控制器中调用showSpinner时

self.showSpinner(onView: self.view)
downloadFromServer(url: imageName)
self.removeSpinner()

显示和删除微调功能仅显示加载屏幕。这是行不通的，因为在从数据库中获取所有图像之前，我的downloadFromServer函数已经退出，我只能看到加载屏幕一秒钟。在将所有图像都附加到mageArrayWatch数组时，如何使加载屏幕完成？

Answer 1

您需要一个调度组

var imageArrayWatch = [UIImage]()

func downloadFromServer(url: [String], imageNumber: Int){
    let g = DispatchGroup()      ////// 1
    for i in url{
    let i = URL(string: i)
        print("I" , i)
        g.enter()         ////// 2
        URLSession.shared.dataTask(with: i!) { data, response, error in
         guard
             let httpURLResponse = response as? HTTPURLResponse, httpURLResponse.statusCode == 200,
             let data = data, error == nil,
             let image = UIImage(data: data)

            else {  g.leave() ;   return }   ////// 3
            print("Here", image)
         DispatchQueue.main.async() {
                print("Appended")
            self.imageArrayWatch.append(image)
            g.leave()    ////// 4
         }
         }.resume()
    }

    g.notify(queue: .main) {       ////// 5

        // stop loading here

    }
}

从Firebase下载图像时正在加载屏幕

1 个答案: