创建加载图像/活动指示器，直到图像以swift显示在屏幕上

我想在从网站url下载图像时在屏幕上显示活动指示器，然后在图像中显示。图像这是我下面的代码。每次我下载图像时，它会立即打印状态，而活动指示器永远不会出现。我一直在网上搜索，但我还是不明白。请帮忙

 let mygroup = DispatchGroup()
 var activityIndicator = UIActivityIndicatorView()

func downloadpic(sender:UIButton){
    let catPictureURL = URL(string: addr)!

    // Creating a session object with the default configuration.
    // You can read more about it here https://developer.apple.com/reference/foundation/urlsessionconfiguration
    let session = URLSession(configuration: .default)

    // Define a download task. The download task will download the contents of the URL as a Data object and then you can do what you wish with that data.

    let downloadPicTask = session.dataTask(with: catPictureURL) { (data, response, error) in
        // The download has finished.
        if let e = error {
            print("Error downloading cat picture: \(e)")
        } else {
            // No errors found.
            // It would be weird if we didn't have a response, so check for that too.
            if let res = response as? HTTPURLResponse {
                // put loading screen here
                self.activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .white)
                self.activityIndicator.frame = CGRect(x: 0, y: 0, width: 46, height: 46)
                self.activityIndicator.startAnimating()
                self.mygroup.enter()
                print("downloading image")
                print("Downloaded cat picture with response code \(res.statusCode)")
                if let imageData = data {
                    // Finally convert that Data into an image and do what you wish with it.
                     self.images.image = UIImage(data: imageData)
                        self.mygroup.leave()
                        print("image already downloaded")
                        self.activityIndicator.stopAnimating()
                        self.activityIndicator.hidesWhenStopped = true


                    // Do something with your image.
                } else {
                    print("Couldn't get image: Image is nil")
                }
            } else {
                print("Couldn't get response code for some reason")
            }
        }
    }

    downloadPicTask.resume()
}

---

您遇到了这个问题，因为：

您没有将

活动指示器添加到任何视图中

您在

completionHandler

块中配置了

activityIndicator

让我们在

activityIndicator

中配置

viewDidLoad（）

方法：

self.activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .gray)
self.activityIndicator.frame = CGRect(x: 0, y: 0, width: 46, height: 46)
self.activityIndicator.hidesWhenStopped = true

view.addSubview(self.activityIndicator)

并在恢复

dataTask

self.activityIndicator.startAnimating()

然后，在

completionHandler

self.activityIndicator.stopAnimating()

最终代码：

let mygroup = DispatchGroup()
var activityIndicator = UIActivityIndicatorView()

override func viewDidLoad() {
    super.viewDidLoad()

    self.activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .gray)
    self.activityIndicator.frame = CGRect(x: 0, y: 0, width: 46, height: 46)
    self.activityIndicator.hidesWhenStopped = true

    view.addSubview(self.activityIndicator)
}

func downloadpic(sender: UIButton) {
    let catPictureURL = URL(string: addr)!

    // Creating a session object with the default configuration.
    // You can read more about it here https://developer.apple.com/reference/foundation/urlsessionconfiguration
    let session = URLSession(configuration: .default)

    // Define a download task. The download task will download the contents of the URL as a Data object and then you can do what you wish with that data.

    self.activityIndicator.startAnimating()

    let downloadPicTask = session.dataTask(with: catPictureURL) { (data, response, error) in
        // The download has finished.
        if let e = error {
            print("Error downloading cat picture: \(e)")
        } else {
            // No errors found.
            // It would be weird if we didn't have a response, so check for that too.
            if let res = response as? HTTPURLResponse {
                // put loading screen here

                self.mygroup.enter()
                print("downloading image")
                print("Downloaded cat picture with response code \(res.statusCode)")
                if let imageData = data {
                    // Finally convert that Data into an image and do what you wish with it.
                    self.images.image = UIImage(data: imageData)
                    self.mygroup.leave()
                    print("image already downloaded")
                    self.activityIndicator.stopAnimating()

                    // Do something with your image.
                } else {
                    print("Couldn't get image: Image is nil")
                }
            } else {
                print("Couldn't get response code for some reason")
            }
        }
    }

    downloadPicTask.resume()
}

结果

---

您遇到了这个问题，因为：

您没有将

活动指示器添加到任何视图中

您在

completionHandler

块中配置了

activityIndicator

让我们在

activityIndicator

中配置

viewDidLoad（）

方法：

self.activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .gray)
self.activityIndicator.frame = CGRect(x: 0, y: 0, width: 46, height: 46)
self.activityIndicator.hidesWhenStopped = true

view.addSubview(self.activityIndicator)

并在恢复

dataTask

self.activityIndicator.startAnimating()

然后，在

completionHandler

self.activityIndicator.stopAnimating()

最终代码：

let mygroup = DispatchGroup()
var activityIndicator = UIActivityIndicatorView()

override func viewDidLoad() {
    super.viewDidLoad()

    self.activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: .gray)
    self.activityIndicator.frame = CGRect(x: 0, y: 0, width: 46, height: 46)
    self.activityIndicator.hidesWhenStopped = true

    view.addSubview(self.activityIndicator)
}

func downloadpic(sender: UIButton) {
    let catPictureURL = URL(string: addr)!

    // Creating a session object with the default configuration.
    // You can read more about it here https://developer.apple.com/reference/foundation/urlsessionconfiguration
    let session = URLSession(configuration: .default)

    // Define a download task. The download task will download the contents of the URL as a Data object and then you can do what you wish with that data.

    self.activityIndicator.startAnimating()

    let downloadPicTask = session.dataTask(with: catPictureURL) { (data, response, error) in
        // The download has finished.
        if let e = error {
            print("Error downloading cat picture: \(e)")
        } else {
            // No errors found.
            // It would be weird if we didn't have a response, so check for that too.
            if let res = response as? HTTPURLResponse {
                // put loading screen here

                self.mygroup.enter()
                print("downloading image")
                print("Downloaded cat picture with response code \(res.statusCode)")
                if let imageData = data {
                    // Finally convert that Data into an image and do what you wish with it.
                    self.images.image = UIImage(data: imageData)
                    self.mygroup.leave()
                    print("image already downloaded")
                    self.activityIndicator.stopAnimating()

                    // Do something with your image.
                } else {
                    print("Couldn't get image: Image is nil")
                }
            } else {
                print("Couldn't get response code for some reason")
            }
        }
    }

    downloadPicTask.resume()
}

结果

---

我建议您使用类似AlamofireImage的库，并在UIImageView中选择自定义类

创建UIImageView的自定义类：

import Foundation
import UIKit
import AlamofireImage

class CustomImageView: UIImageView {

    func ImageViewLoading(mediaUrl: String) {
        guard let url = URL(string: mediaUrl) else { return }
        let activityIndicator = self.activityIndicator
        DispatchQueue.main.async {
            activityIndicator.startAnimating()
        }
        self.af.setImage(
            withURL: url,
            placeholderImage: nil,
            filter: nil,
            completion: { response in
                DispatchQueue.main.async {
                    activityIndicator.stopAnimating()
                    activityIndicator.removeFromSuperview()
                }
            }
        )
    }

    private var activityIndicator: UIActivityIndicatorView {
        let activityIndicator = UIActivityIndicatorView()
        activityIndicator.hidesWhenStopped = true
        activityIndicator.color = UIColor.black
        self.addSubview(activityIndicator)

        activityIndicator.translatesAutoresizingMaskIntoConstraints = false

        let centerX = NSLayoutConstraint(item: self,
                                         attribute: .centerX,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerX,
                                         multiplier: 1,
                                         constant: 0)
        let centerY = NSLayoutConstraint(item: self,
                                         attribute: .centerY,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerY,
                                         multiplier: 1,
                                         constant: 0)
        self.addConstraints([centerX, centerY])
        return activityIndicator
    }

}

@IBOutlet weak var photoImageViewWithLoading: CustomImageView!

photoImageViewWithLoading.ImageViewLoading(mediaUrl: mediaUrl!)

将此类用于UIImageView：

import Foundation
import UIKit
import AlamofireImage

class CustomImageView: UIImageView {

    func ImageViewLoading(mediaUrl: String) {
        guard let url = URL(string: mediaUrl) else { return }
        let activityIndicator = self.activityIndicator
        DispatchQueue.main.async {
            activityIndicator.startAnimating()
        }
        self.af.setImage(
            withURL: url,
            placeholderImage: nil,
            filter: nil,
            completion: { response in
                DispatchQueue.main.async {
                    activityIndicator.stopAnimating()
                    activityIndicator.removeFromSuperview()
                }
            }
        )
    }

    private var activityIndicator: UIActivityIndicatorView {
        let activityIndicator = UIActivityIndicatorView()
        activityIndicator.hidesWhenStopped = true
        activityIndicator.color = UIColor.black
        self.addSubview(activityIndicator)

        activityIndicator.translatesAutoresizingMaskIntoConstraints = false

        let centerX = NSLayoutConstraint(item: self,
                                         attribute: .centerX,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerX,
                                         multiplier: 1,
                                         constant: 0)
        let centerY = NSLayoutConstraint(item: self,
                                         attribute: .centerY,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerY,
                                         multiplier: 1,
                                         constant: 0)
        self.addConstraints([centerX, centerY])
        return activityIndicator
    }

}

@IBOutlet weak var photoImageViewWithLoading: CustomImageView!

photoImageViewWithLoading.ImageViewLoading(mediaUrl: mediaUrl!)

从url加载图像时，UIImageView将显示activityindicator

我有这个答案会帮助你的

---

注意：我使用Swift 5

我建议您使用类似AlamofireImage的库，并在UIImageView中选择自定义类

创建UIImageView的自定义类：

import Foundation
import UIKit
import AlamofireImage

class CustomImageView: UIImageView {

    func ImageViewLoading(mediaUrl: String) {
        guard let url = URL(string: mediaUrl) else { return }
        let activityIndicator = self.activityIndicator
        DispatchQueue.main.async {
            activityIndicator.startAnimating()
        }
        self.af.setImage(
            withURL: url,
            placeholderImage: nil,
            filter: nil,
            completion: { response in
                DispatchQueue.main.async {
                    activityIndicator.stopAnimating()
                    activityIndicator.removeFromSuperview()
                }
            }
        )
    }

    private var activityIndicator: UIActivityIndicatorView {
        let activityIndicator = UIActivityIndicatorView()
        activityIndicator.hidesWhenStopped = true
        activityIndicator.color = UIColor.black
        self.addSubview(activityIndicator)

        activityIndicator.translatesAutoresizingMaskIntoConstraints = false

        let centerX = NSLayoutConstraint(item: self,
                                         attribute: .centerX,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerX,
                                         multiplier: 1,
                                         constant: 0)
        let centerY = NSLayoutConstraint(item: self,
                                         attribute: .centerY,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerY,
                                         multiplier: 1,
                                         constant: 0)
        self.addConstraints([centerX, centerY])
        return activityIndicator
    }

}

@IBOutlet weak var photoImageViewWithLoading: CustomImageView!

photoImageViewWithLoading.ImageViewLoading(mediaUrl: mediaUrl!)

将此类用于UIImageView：

import Foundation
import UIKit
import AlamofireImage

class CustomImageView: UIImageView {

    func ImageViewLoading(mediaUrl: String) {
        guard let url = URL(string: mediaUrl) else { return }
        let activityIndicator = self.activityIndicator
        DispatchQueue.main.async {
            activityIndicator.startAnimating()
        }
        self.af.setImage(
            withURL: url,
            placeholderImage: nil,
            filter: nil,
            completion: { response in
                DispatchQueue.main.async {
                    activityIndicator.stopAnimating()
                    activityIndicator.removeFromSuperview()
                }
            }
        )
    }

    private var activityIndicator: UIActivityIndicatorView {
        let activityIndicator = UIActivityIndicatorView()
        activityIndicator.hidesWhenStopped = true
        activityIndicator.color = UIColor.black
        self.addSubview(activityIndicator)

        activityIndicator.translatesAutoresizingMaskIntoConstraints = false

        let centerX = NSLayoutConstraint(item: self,
                                         attribute: .centerX,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerX,
                                         multiplier: 1,
                                         constant: 0)
        let centerY = NSLayoutConstraint(item: self,
                                         attribute: .centerY,
                                         relatedBy: .equal,
                                         toItem: activityIndicator,
                                         attribute: .centerY,
                                         multiplier: 1,
                                         constant: 0)
        self.addConstraints([centerX, centerY])
        return activityIndicator
    }

}

@IBOutlet weak var photoImageViewWithLoading: CustomImageView!

photoImageViewWithLoading.ImageViewLoading(mediaUrl: mediaUrl!)

从url加载图像时，UIImageView将显示activityindicator

我有这个答案会帮助你的

---

注意：我使用Swift 5

我编写了一个使用SDWebImage的扩展。下面是我的代码，给出了一个很好的用户体验

import SDWebImage

extension UIImageView {    
    func imageURL(_ url: String) {
        let activityIndicator = UIActivityIndicatorView(style: .gray)
        activityIndicator.frame = CGRect(x: 0, y: 0, width: 64, height: 64)
        activityIndicator.hidesWhenStopped = true
        activityIndicator.startAnimating()
        activityIndicator.translatesAutoresizingMaskIntoConstraints = false
        
        activityIndicator.center = CGPoint(x: self.frame.size.width  / 2, y: self.frame.size.height / 2)
        
        self.addSubview(activityIndicator)
        
        //self.sd_setImage(with: URL(string: url), placeholderImage: UIImage(named: "placeholder.png"))
        self.sd_setImage(with: URL(string: url)) { (image, error, cacheType, url) in
            activityIndicator.stopAnimating()
        }
    }
}

---

我编写了一个使用SDWebImage的扩展。下面是我的代码，给出了一个很好的用户体验

import SDWebImage

extension UIImageView {    
    func imageURL(_ url: String) {
        let activityIndicator = UIActivityIndicatorView(style: .gray)
        activityIndicator.frame = CGRect(x: 0, y: 0, width: 64, height: 64)
        activityIndicator.hidesWhenStopped = true
        activityIndicator.startAnimating()
        activityIndicator.translatesAutoresizingMaskIntoConstraints = false
        
        activityIndicator.center = CGPoint(x: self.frame.size.width  / 2, y: self.frame.size.height / 2)
        
        self.addSubview(activityIndicator)
        
        //self.sd_setImage(with: URL(string: url), placeholderImage: UIImage(named: "placeholder.png"))
        self.sd_setImage(with: URL(string: url)) { (image, error, cacheType, url) in
            activityIndicator.stopAnimating()
        }
    }
}

---

我已经看到了活动指示器，但我没有将其包含在上面，因为问题是活动指示器启动后立即停止。我试图做的是在图像仍在下载时显示活动指示器。我需要使活动指示器在应用程序下载图像时启动，然后在图像显示在图像中后停止。图像查看我的附件！我想这就是你想要的。你是对的，对不起我的错误。谢谢你的回答。我已经看到了活动指示器。我没有把它包括在上面，因为问题是活动指示器启动后立即停止。我试图做的是在图像仍在下载时显示活动指示器。我需要使活动指示器在应用程序下载图像时启动，然后在图像显示在图像中后停止。图像查看我的附件！我想这就是你想要的。你是对的，对不起我的错误。谢谢您的回答。这是在UICollectionView中设置单元格活动指示器的便捷方法，但设置单元格中心的指示器需要设置。将AutoResizezingMaskintoConstraints=true。若要将指示器设置为中心，请将类似的内容替换为activityIndicator.center=CGPoint（x:self.frame.size.width/2，y:self.frame.size.height/2）到activityIndicator.center=self.center这是在UICollectionView中设置活动指示器到单元格的便捷方法，但为了将指示器设置到单元的中心，需要设置指示器。TranslatesAutoResizezingMaskintoConstraints=true。若要将指示器设置为中心，请使用activityIndicator.center=CGPoint（x:self.frame.size.width/2，y:self.frame.size.height/2）将此类似项替换为activityIndicator.center=self.center