Objective C: Keep Image After App Termination - ios

Question

I am making an app that downloads files from an online server by clicking an Icon representing the file to be downloaded, then the file will be saved to the app's sandbox.
I have managed to do those mentioned above. Now, what I want to do is to put a "Check" image on the icon to allude the user that it is already downloaded.
I already tried it by putting another UIImageViewon top of the icon when the download is successful but when I fully terminate the app and re-open it, the image is gone and I need to download it again to show it.
How will I able to that?

Answer 1

Just keep an array of all the downloaded files, and at startup check to see which files to apply the check mark to.
For example:
When you get the image:
NSMutableArray *array;
array = [[NSUserDefaults standardUserDefaults] objectForKey:#"downloaded"].mutableCopy;
if (!array) array = [[NSMutableArray alloc] init];
[array addObject:somethingToIdentifyTheImageBy]; //For example, a string with the name of the image
[[NSUserDefaults standardUserDefaults] setObject:array forKey:#"downloaded"]
On startup:
NSArray *downloadedImages = [[NSUserDefaults standardUserDefaults] objectForKey:#"downloaded"];
forin (NSString *string in downloadedImages)
{
//Apply check mark
}

Answer 2

Use following code to Save your Downloaded Image to Library Directory of Device and Retrive it, as NSUserDefaults will not allow you to store Large amount of Data.
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSLibraryDirectory, NSUserDomainMask, YES);
NSString *libraryDirectory = paths[0];
NSString *imageFilePath = [libraryDirectory stringByAppendingPathComponent:#"myImageIcon.jpg"];
NSError *error;
if (![[NSFileManager defaultManager] fileExistsAtPath:imageFilePath]) {
// File Exist at Library Directory, Just Read it.
NSData *imageData = [NSData dataWithContentsOfFile:imageFilePath];
}
else
{
// File Doesn't Exist at Library Directory, Download it From Server
NSURL *url = [NSURL URLWithString:#"YOUR Image File URL"];
NSData *imageData = [NSData dataWithContentsOfURL:url];
NSString *imagePath = [libraryDirectory stringByAppendingPathComponent:[url lastPathComponent]];
NSLog(#"Image Stored At %#",imagePath);
[imageData writeToFile:imagePath atomically:YES];
}

Answer 3

You cannot save anything inside the app's bundle, but you can store the image in your app's documents directory by using [NSData dataWithContentsOfURL:] method. This is not exactly permanent, but it stays there at least until the user deletes the app.
NSData *imageData = [NSData dataWithContentsOfURL:myImageURL];
NSString *imagePath = [[NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0] stringByAppendingPathComponent:#"/myImage.png"];
[imageData writeToFile:imagePath atomically:YES];