Asyc image download with core data - ios

Question

I'm wondering how to do this in proper way.
I have NSManagedObject which contains properties: name, imageUrl, iconUrl.
I'm using category to update this object:
#implementation MyObject (Create)
+ (instancetype)findOrCreateWithIdentifier:(id)identifier inContext:(NSManagedObjectContext*)context {
NSString* entityName = NSStringFromClass(self);
NSFetchRequest* fetchRequest = [NSFetchRequest fetchRequestWithEntityName:entityName];
fetchRequest.predicate = [NSPredicate predicateWithFormat:#"name = %#", identifier];
fetchRequest.fetchLimit = 1;
id object = [[context executeFetchRequest:fetchRequest error:NULL] lastObject];
if(object == nil) {
object = [NSEntityDescription insertNewObjectForEntityForName:entityName inManagedObjectContext:context];
}
return object;
}
+ (void)createWithJSONComponents:(NSDictionary*)components intoContext:(NSManagedObjectContext*)context
{
NSString* name = components[#"name"];
NSString* imageUrl = components[#"image"];
NSString* iconUrl = components[#"icon"];
MyObject* myObject = [self findOrCreateWithIdentifier:myObject inContext:context];
if(!myObject.name)
{
myObject.name = name;
}
if(![imageUrl isEqualToString:myObject.imageURL]
|| !myObject.imageURL )
{
myObject.imageURL = imageUrl;
//TODO remove old image and get new one
//TODO2 in block callback after download myImageNameWithMD5 = imageNameWithMD5
}
if(![iconUrl isEqualToString:myObject.iconUrl]
|| !myObject.iconUrl)
{
myObject.iconUrl = imageUrl;
//TODO remove old image and get new one
//TODO2 in block callback after download myImageNameWithMD5 = imageNameWithMD5
}
}
I'm refreshing my tableView with fetchResultDelegate.
Now I have few questions. Would it be a proper way to get images in my //TODO sections with async download? Will fetchResultDelegate inform me that images are set if I will execute //TODO2 code? Or should I do it sync with thread which is adding those managedObject.
And finally how to stop imageDownload if app is killed?
Or should I do this download in my model class in myImageNameWithMD5 setter method?

Answer 1

I think that the real image should be seperated from the CoreData DataBase.
Because you might never actually going to show the user.
My approach is that only download the image when user is about to see it, and with third
party framework like SDWebImage, that couldn't be easier.
It handles the download, update, cache and display automatically.

Answer 2

This is similar to this.
However, I would not mix async operations with item creation.
I would create a "TODO" object (lets call it ImageToDownload) with a to-one relationship with the created/updated object.
I would create a manager that listen to the creation of such "TODO" objects and issue the download of images from it using NSOperations.
on successful creation you delete the "TODO" object.
This will allow you both to cancel image downloading when you need to, and also the download request is persisted and might be continued at a later time.

Answer 3

Ok, I've found the best solution (thanks to #Kyle Fang)
Im using SDWebImage Framework. In place where I'm filling my UIView with data I've used
[view.iconImageView setImageWithURL:[NSURL URLWithString:item.iconUrl]
placeholderImage:[UIImage imageNamed:#"placeholder.png"]];
And in my NSManagedObjectCategory in place of //TODO I'm using this code:
[[SDImageCache sharedImageCache] removeImageForKey:myObject.iconUrl];