Swift - Write Image from URL to Local File

Question

I've been learning swift rather quickly, and I'm trying to develop an OS X application that downloads images.

I've been able to parse the JSON I'm looking for into an array of URLs as follows:

func didReceiveAPIResults(results: NSArray) {
    println(results)
    for link in results {
        let stringLink = link as String
        //Check to make sure that the string is actually pointing to a file
        if stringLink.lowercaseString.rangeOfString(".jpg") != nil {2

            //Convert string to url
            var imgURL: NSURL = NSURL(string: stringLink)!

            //Download an NSData representation of the image from URL
            var request: NSURLRequest = NSURLRequest(URL: imgURL)

            var urlConnection: NSURLConnection = NSURLConnection(request: request, delegate: self)!
            //Make request to download URL
            NSURLConnection.sendAsynchronousRequest(request, queue: NSOperationQueue.mainQueue(), completionHandler: { (response: NSURLResponse!, data: NSData!, error: NSError!) -> Void in
                if !(error? != nil) {
                    //set image to requested resource
                    var image = NSImage(data: data)

                } else {
                    //If request fails...
                    println("error: \(error.localizedDescription)")
                }
            })
        }
    }
}

So at this point I have my images defined as "image", but what I'm failing to grasp here is how to save these files to my local directory.

Any help on this matter would be greatly appreciated!

Thanks,

tvick47

Solution 1

The following code would write a UIImage in the Application Documents directory under the filename 'filename.jpg'

var image = ....  // However you create/get a UIImage
let documentsPath = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as String
let destinationPath = documentsPath.stringByAppendingPathComponent("filename.jpg")
UIImageJPEGRepresentation(image,1.0).writeToFile(destinationPath, atomically: true)

Solution 2

In Swift 3:

Write

do {
    let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
    let fileURL = documentsURL.appendingPathComponent("\(fileName).png")
    if let pngImageData = UIImagePNGRepresentation(image) {
    try pngImageData.write(to: fileURL, options: .atomic)
    }
} catch { }

Read

let documentsURL = FileManager.default.urls(for: .documentDirectory, in: .userDomainMask).first!
let filePath = documentsURL.appendingPathComponent("\(fileName).png").path
if FileManager.default.fileExists(atPath: filePath) {
    return UIImage(contentsOfFile: filePath)
}

Solution 3

In swift 2.0, stringByAppendingPathComponent is unavailable, so the answer changes a bit. Here is what I've done to write a UIImage out to disk.

documentsURL = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask).first!
if let image = UIImage(data: someNSDataRepresentingAnImage) {
    let fileURL = documentsURL.URLByAppendingPathComponent(fileName+".png")
    if let pngImageData = UIImagePNGRepresentation(image) {
        pngImageData.writeToURL(fileURL, atomically: false)
    }
}

Solution 4

UIImagePNGRepresentaton() function had been deprecated. try image.pngData()

View more solutions

Comments

[Tyler]

Thanks for the response! However, whenever I try to build with that code I receive the error: Use of unresolved identifier 'UIImageJPEGRepresentation'

[kurtn718]

That function exists on iOS. Here's how to do it using Mac APIs in Objective-C. Will post Swift version stackoverflow.com/questions/3038820/…

[Tyler]

Thanks for the update! Although I do understand a bit further, a swift version would really help me out. Thanks!

[Gargo]

String doesn't have stringByAppendingPathComponent

[moonvader]

great answer - please consider to add info about image deletion

[jamryu]

I am trying to use UIImagePNGRepresentation() function but Xcode does not recognize it for some reason. I am using Swift 4.2.

[Karthi Rasu]

try pngData() PNG is changed