I'm trying to download and save some images (converted from a base64 string to UIImage) to the device and keep getting a Memory warning.
ontracFullScreenImageViewController *etrackDiagrams = ((ontracFullScreenImageViewController*)[viewControllerDictionary objectForKey:@"E-track Diagrams"]);
NSMutableSet *etrackSet = [[NSMutableSet alloc] init];
for (UIImage *image in etrackDiagrams.imageArray) {
NSAutoreleasePool *localPool = [[NSAutoreleasePool alloc] init];
//convert the image to NSData and store it in the documents directory
NSData *pngData = UIImagePNGRepresentation(image);
NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
NSString *documentsPath = [paths objectAtIndex:0]; //Get the docs directory
NSString * timeInMS = [NSString stringWithFormat:@"%lld", [@(floor([[NSDate date] timeIntervalSince1970] * 1000)) longLongValue]];
NSString *filePath = [documentsPath stringByAppendingPathComponent:[ NSString stringWithFormat:@"%@_%@_etrack_diagram_%i_%i_image.png", delegate.userName, timeInMS, self.dataObject.dataPack.pack_id, [etrackDiagrams.imageViewArray indexOfObject:image]]]; //Add the file name
[pngData writeToFile:filePath atomically:YES];
NSLog(@"filepath %@", filePath);
NSString *currSysVer = [[UIDevice currentDevice] systemVersion];
if ([currSysVer isEqualToString:@"5.0.1"]) {
[[NSURL URLWithString:filePath] setResourceValue: [NSNumber numberWithBool: YES] forKey: NSURLIsExcludedFromBackupKey error: &error];
}
//Add the file Path to ImageLinks
[etrackDiagrams.imageLinks addObject:filePath];
//save the image location in Core Data
EtrackDiagram *etrackDiagram = [NSEntityDescription
insertNewObjectForEntityForName:@"EtrackDiagram"
inManagedObjectContext:context];
etrackDiagram.locationString = filePath;
etrackDiagram.dataObject = dataObject;
[etrackSet addObject:etrackDiagram];
[dataObject addEtrackDiagramsObject:etrackDiagram];
[localPool drain];
}
[dataObject addEtrackDiagrams: etrackSet];
The memory warning occurs at NSData *pngData = UIImagePNGRepresentation(image); as the images are quite large.
Unfortunately I can't control the size of the images but need a way to save them to the device to use them in a gallery later on.
I have tried to wrap the code with @autoreleasepool but it made no difference.
The real problem is this line:
for (UIImage *image in etrackDiagrams.imageArray) {
This implies you are holding an array of images in memory. That is always dangerous. You need to have saved all these images on disk and load them into memory one at a time (and in a noncaching way). Your goal should be to have at most one image in memory at a time.