How to Store the online images and data for offline purpose

Question

I have to build an iPhone app that check for the net connectivity and whenever it get it has an online sync with a web service, it downloads X images and saves them into the device.

Then, in offline mode, I have to load the images in collectionview for that i have to store images somewhere.Same For data also

I am using .net webservice with json response.

I was thinking about the Core Data storage, is that possible? Maybe storing images in core data database will slow down the app?

Answer 1

You have to download and save each received image in the application directory, then you save in CoreData the path to those images.

// Save image to disk
    NSString *documentaryPath = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) objectAtIndex:0];
    NSString *filePath = [NSString stringWithFormat:@"%@/Image.png",documentaryPath];
    NSData *data = [NSData dataWithData:UIImagePNGRepresentation(YOUR_IMAGE)];
    [data writeToFile:filePath atomically:YES];

// Retrieve the Image
- (NSData *) imageData {

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

    NSString *pngFilePath = [NSString stringWithFormat:@"%@/Image.png",docDir];

    NSData *dataImage = [NSData dataWithContentsOfFile:pngFilePath];

    return dataImage;
}

And use like below.

UIImage *image = [UIImage imageWithData:imageData]

May be it will help you.

Answer 2

Yes,it is possible,but not worthwhile.

As usually,we cache an image with follow steps:

1. Check whether we have load the image at the specific URL,if yes,go step 2 ,otherwise,go step 3
2. Load the image from file.
3. DownLoad the image,and save it to file. you should give the image file a name associated with its URL,so you can find it by the url next time .

There is a tool can do bellow work well,you can try using SDWebImage .

Answer 3

Yes you can store images in core data in the form of Binary Data, here is an example of how to do it link ! As far as speed is concerned core data will not slow down your app performance but it usually takes more space than sqlite, here's a link ! that show comparison between core data and sqlite performance.