Storing images locally on an iOS device

Question

Some iOS photo-related apps store images created with the app somewhere other than the photo library. For example Fat Booth shows a scrolling list of photos created with the

Answer 1

You can do it with core data by storing binary data, but its not recommended. There is a much better way - especially for photos. Your application has a documents/file directory that only your app can access. I recommend starting here for the concepts and how to access it. Its relatively straightforward. You may want to combine this with core data to store file paths, metadata, etc. http://developer.apple.com/library/mac/#documentation/FileManagement/Conceptual/FileSystemProgrammingGUide/FileSystemOverview/FileSystemOverview.html

Answer 2

The simplest way is to save it in the app's Documents directory and save the path with NSUserDefaults like so:

NSData *imageData = UIImagePNGRepresentation(newImage);

NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsDirectory = [paths objectAtIndex:0];

NSString *imagePath =[documentsDirectory stringByAppendingPathComponent:[NSString stringWithFormat:@"%@.png",@"cached"]];

NSLog(@"pre writing to file");
if (![imageData writeToFile:imagePath atomically:NO]) 
{
    NSLog(@"Failed to cache image data to disk");
}
else
{
    NSLog(@"the cachedImagedPath is %@",imagePath); 
}

Then save the imagePath in some dictionary in NSUserDefaults or however you'd like, and then to retrieve it just do:

 NSString *theImagePath = [yourDictionary objectForKey:@"cachedImagePath"];
 UIImage *customImage = [UIImage imageWithContentsOfFile:theImagePath];

Answer 3

For Swift:

let imageData = UIImagePNGRepresentation(selectedImage)
let paths = NSSearchPathForDirectoriesInDomains(.DocumentDirectory, .UserDomainMask, true)[0] as String
let imagePath = paths.stringByAppendingPathComponent("cached.png")

if !imageData.writeToFile(imagePath, atomically: false)
{
   println("not saved")
} else {
   println("saved")
   NSUserDefaults.standardUserDefaults().setObject(imagePath, forKey: "imagePath")
}

For Swift 2.1:

let imageData = UIImagePNGRepresentation(selectedImage)
let documentsURL = NSFileManager.defaultManager().URLsForDirectory(.DocumentDirectory, inDomains: .UserDomainMask)[0]
let imageURL = documentsURL.URLByAppendingPathComponent("cached.png")

if !imageData.writeToURL(imageURL, atomically: false)
{
    print("not saved")
} else {
    print("saved")
    NSUserDefaults.standardUserDefaults().setObject(imageData, forKey: "imagePath")
}

stringByAppendingPathComponent is unavailable in Swift 2.1 so you can use URLByAppendingPathComponent. Get more info here.