I was working on a project which loads a gif to UIImageView from its url.

while running app in the Xcode gives a strange warning and the gif also looks laggy.

Warning is like:

Synchronous URL loading of https://mir-s3-cdn-cf.behance.net/project_modules/max_1200/5eeea355389655.59822ff824b72.gif should not occur on this application's main thread as it may lead to UI unresponsiveness. Please switch to an asynchronous networking API such as URLSession.

The code snippet I've used for loading gif with url.

//
//  iOSDevCenters GIF.swift
//  Get Fit
//
//  Created by Sandeep Sahani on 08/12/22.
//

import UIKit
import ImageIO
// FIXME: comparison operators with optionals were removed from the Swift Standard Libary.
// Consider refactoring the code to use the non-optional operators.
fileprivate func < <T : Comparable>(lhs: T?, rhs: T?) -> Bool {
  switch (lhs, rhs) {
  case let (l?, r?):
    return l < r
  case (nil, _?):
    return true
  default:
    return false
  }
}

extension UIImage {
    
    public class func gifImageWithData(_ data: Data) -> UIImage? {
        guard let source = CGImageSourceCreateWithData(data as CFData, nil) else {
            print("image doesn't exist")
            return nil
        }
        
        return UIImage.animatedImageWithSource(source)
    }
    
    public class func gifImageWithURL(_ gifUrl:String) -> UIImage? {
        guard let bundleURL:URL? = URL(string: gifUrl)
            else {
                print("image named \"\(gifUrl)\" doesn't exist")
                return nil
        }
        guard let imageData = try? Data(contentsOf: bundleURL!) else {
            print("image named \"\(gifUrl)\" into NSData")
            return nil
        }
        
        return gifImageWithData(imageData)
    }
    
    public class func gifImageWithName(_ name: String) -> UIImage? {
        guard let bundleURL = Bundle.main
            .url(forResource: name, withExtension: "gif") else {
                print("SwiftGif: This image named \"\(name)\" does not exist")
                return nil
        }
        guard let imageData = try? Data(contentsOf: bundleURL) else {
            print("SwiftGif: Cannot turn image named \"\(name)\" into NSData")
            return nil
        }
        
        return gifImageWithData(imageData)
    }
    
    class func delayForImageAtIndex(_ index: Int, source: CGImageSource!) -> Double {
        var delay = 0.1
        
        let cfProperties = CGImageSourceCopyPropertiesAtIndex(source, index, nil)
        let gifProperties: CFDictionary = unsafeBitCast(
            CFDictionaryGetValue(cfProperties,
                Unmanaged.passUnretained(kCGImagePropertyGIFDictionary).toOpaque()),
            to: CFDictionary.self)
        
        var delayObject: AnyObject = unsafeBitCast(
            CFDictionaryGetValue(gifProperties,
                Unmanaged.passUnretained(kCGImagePropertyGIFUnclampedDelayTime).toOpaque()),
            to: AnyObject.self)
        if delayObject.doubleValue == 0 {
            delayObject = unsafeBitCast(CFDictionaryGetValue(gifProperties,
                Unmanaged.passUnretained(kCGImagePropertyGIFDelayTime).toOpaque()), to: AnyObject.self)
        }
        
        delay = delayObject as! Double
        
        if delay < 0.1 {
            delay = 0.1
        }
        
        return delay
    }
    
    class func gcdForPair(_ a: Int?, _ b: Int?) -> Int {
        var a = a
        var b = b
        if b == nil || a == nil {
            if b != nil {
                return b!
            } else if a != nil {
                return a!
            } else {
                return 0
            }
        }
        
        if a < b {
            let c = a
            a = b
            b = c
        }
        
        var rest: Int
        while true {
            rest = a! % b!
            
            if rest == 0 {
                return b!
            } else {
                a = b
                b = rest
            }
        }
    }
    
    class func gcdForArray(_ array: Array<Int>) -> Int {
        if array.isEmpty {
            return 1
        }
        
        var gcd = array[0]
        
        for val in array {
            gcd = UIImage.gcdForPair(val, gcd)
        }
        
        return gcd
    }
    
    class func animatedImageWithSource(_ source: CGImageSource) -> UIImage? {
        let count = CGImageSourceGetCount(source)
        var images = [CGImage]()
        var delays = [Int]()
        
        for i in 0..<count {
            if let image = CGImageSourceCreateImageAtIndex(source, i, nil) {
                images.append(image)
            }
            
            let delaySeconds = UIImage.delayForImageAtIndex(Int(i),
                source: source)
            delays.append(Int(delaySeconds * 1000.0)) // Seconds to ms
        }
        
        let duration: Int = {
            var sum = 0
            
            for val: Int in delays {
                sum  = val
            }
            
            return sum
        }()
        
        let gcd = gcdForArray(delays)
        var frames = [UIImage]()
        
        var frame: UIImage
        var frameCount: Int
        for i in 0..<count {
            frame = UIImage(cgImage: images[Int(i)])
            frameCount = Int(delays[Int(i)] / gcd)
            
            for _ in 0..<frameCount {
                frames.append(frame)
            }
        }
        
        let animation = UIImage.animatedImage(with: frames,
            duration: Double(duration) / 1000.0)
        
        return animation
    }
}

Place I have used the code.

//
//  GifViewController.swift
//  Get Fit
//
//  Created by Sandeep Sahani on 08/12/22.
//

import UIKit

class GifViewController: UIViewController
{
    @IBOutlet weak var gif: UIImageView!
    
    override func viewDidLoad()
    {
        super.viewDidLoad()
        
        let gifURL : String = "https://mir-s3-cdn-cf.behance.net/project_modules/max_1200/5eeea355389655.59822ff824b72.gif"
        let imageURL = UIImage.gifImageWithURL(gifURL)
        self.gif.image = imageURL
        
    }
}

How can I remove that strange warning and make that gif smooth?

CodePudding user response：

The API call you're using is executed on the main thread so the system warns you about that.

I'd recommend using modern projects' default choice library for loading remote images called Kingfisher: https://github.com/onevcat/Kingfisher

There is a wiki section on loading gif images with Kingfisher lib:

https://github.com/onevcat/Kingfisher/wiki/Cheat-Sheet#animated-gif

Loading a GIF

let imageView: UIImageView = ...
imageView.kf.setImage(with: URL(string: "your_animated_gif_image_url")!)

or

let imageView = AnimatedImageView()
imageView.kf.setImage(with: URL(string: "your_large_animated_gif_image_url")!)

You have to add Kingfisher to your project as a Swift Package Manager project and then import Kingfisher at the top of the file