iOS: load an image from url

问题

I need to load an image from a url and set it inside an UIImageView; the problem is that I don't know the exact size of the image, then how can I show the image correctly?

回答1:

Just use the size property of UIImage, for example:

NSURL *url = [NSURL URLWithString:path];
NSData *data = [NSData dataWithContentsOfURL:url];
UIImage *img = [[UIImage alloc] initWithData:data];
CGSize size = img.size;

回答2:

In swift:

var url = NSURL.URLWithString("http://www.example.com/picture.png")
var data = NSData(contentsOfURL : url)
var image = UIImage(data : data)
image.size // if you need it

回答3:

In swift regarding using optionals:

var url:NSURL? = NSURL(string: imageString)
var data:NSData? = NSData(contentsOfURL : url!)
var image = UIImage(data : data!)

回答4:

IN SWIFT 3.0

The main thread must be always remain free so it serves the user interface and user interactions.

class ViewController: UIViewController {

@IBOutlet weak var imageView: UIImageView!

private func fetchImage() {
    let imageURL = URL(string: "https://i.stack.imgur.com/9z6nS.png")
    var image: UIImage?
    if let url = imageURL {
        //All network operations has to run on different thread(not on main thread).
        DispatchQueue.global(qos: .userInitiated).async {
            let imageData = NSData(contentsOf: url)
            //All UI operations has to run on main thread.
            DispatchQueue.main.async {
                if imageData != nil {
                    image = UIImage(data: imageData as! Data)
                    self.imageView.image = image
                    self.imageView.sizeToFit()
                } else {
                    image = nil
                }
            }
        }
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    fetchImage()
}

}

回答5:

To download Asynchronous image with Kingfisher library you can follow this step,url :https://github.com/onevcat/Kingfisher:

 func imageFromUrl(_ urlString: String) {
        if let url = URL(string: urlString) {
            ImageDownloader.default.downloadImage(with: url, options: [], progressBlock: nil) {
                (image, error, url, data) in
                DispatchQueue.main.async {
                    self.imageView.image = image
                }
            }
        }
    }

You can also download image with default URLSession.shared.dataTask

 func imageFromUrl(_ urlString: String) {
        if let url = URL(string: urlString) {
            let request = URLRequest(url: url)
            URLSession.shared.dataTask(with: request) {(data,response,error) in
                if let imageData = data as Data? {
                    if let img = UIImage(data: imageData){
                       DispatchQueue.main.async {
                       self.imageView.image = img
                       }
                    }
                }
            }
        }
    }

回答6:

SWIFT 5.0 + fetch on background

private func fetchImage(_ photoURL: URL?) {

    guard let imageURL = photoURL else { return  }

    DispatchQueue.global(qos: .userInitiated).async {
        do{
            let imageData: Data = try Data(contentsOf: imageURL)

            DispatchQueue.main.async {
                let image = UIImage(data: imageData)
                self.userImageView.image = image
                self.userImageView.sizeToFit()
                self.tableView.reloadData()
            }
        }catch{
            print("Unable to load data: \(error)")
        }
    }
}

回答7:

One common mistake in displaying an image downloaded from json or a url is the problem of queues. ALL UI-related things need to be done in the main queue, so if you forgot this, even perfect code (above answers are good) won't display your image on occasion. To call the mainQueue, use code like this, and note that calling main queue might need to be done seperately in the called imageDisplay function:

dispatch_async(dispatch_get_main_queue(), ^{

    self.nameLabel.text = self.pokemon.name;

    [self displayImage];  //CALLS FUNCTION
    self.abilitiesTextView.text = @"loves SwiftUI";
});

- (void)displayImage {            

    NSString *imageURLString = [NSString stringWithFormat: self.pokemon.sprite];
    NSData *imageData = [[NSData alloc] initWithContentsOfURL:[NSURL URLWithString:imageURLString]];
    dispatch_async(dispatch_get_main_queue(), ^{
        self.spriteImageView.image = [UIImage  imageWithData: imageData];
    });

    // NOTE: important for newer versions of XCode/Obj-C...
    //[imageData release];   With ARC ("automated release..."), release method is forbidden, it's already done for you.
}

来源：https://stackoverflow.com/questions/10972555/ios-load-an-image-from-url