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IOS: UIImagePNGRepresentation (). writeToFile does not write to the intended directory

Usage Swift

I am trying to download JPG

from a url and then save this image to a file, but when I try to save it to another directory it fails. It will be downloaded to the application folder Documents

, but not when I try to set the path to another subfolder.

let dir = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0].stringByAppendingPathComponent("SubDirectory") as String
let filepath = dir.stringByAppendingPathComponent("test.jpg")
UIImagePNGRepresentation(UIImage(data: data)).writeToFile(filepath, atomically: true)

When I run this it doesn't save the image on it? Why is this happening? Do I need to create a subfolder beforehand?

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1 answer


A few thoughts:



  • Is there a subdirectory folder? If not, you must create it first. And now it is advisable to use NSURL

    path strings instead. Thus, we get:

    let filename = "test.jpg"
let subfolder = "SubDirectory"

do {
    let fileManager = NSFileManager.defaultManager()
    let documentsURL = try fileManager.URLForDirectory(.DocumentDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: false)
    let folderURL = documentsURL.URLByAppendingPathComponent(subfolder)
    if !folderURL.checkPromisedItemIsReachableAndReturnError(nil) {
        try fileManager.createDirectoryAtURL(folderURL, withIntermediateDirectories: true, attributes: nil)
    }
    let fileURL = folderURL.URLByAppendingPathComponent(filename)

    try imageData.writeToURL(fileURL, options: .AtomicWrite)
} catch {
    print(error)
}

  • I would suggest not converting NSData

    to UIImage

    , and then converting it back to NSData

    . You can just write the original NSData

    object if you like.

    A round trip through process UIImage

    can result in a loss of quality and / or metadata, which could potentially lead to the resulting asset becoming larger, etc. If possible, use the original one NSData

    .

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