Base64 png with Core Data bindings

Question

I have JSON that contains base64 decoded PNG-images that I add to Core Data. I would like to show those images in Image Wells with bindings to my Core Data model.

The problem is that I cannot use Data with NSArchiveFromData since it's been deprecated.

My problem is similar to this but I don't really understand the answer.

Does anyone have an idea?

Thanks

Answer 1

Try something to the effect of this (I'm not sure if you're just using a binding on a property, or using an NSArrayController - I'll try to answer both scenarios)

You could take the string from your json and decode it: (You'll need the open source library referenced in the stackoverflow answer: https://stackoverflow.com/questions/14260936/decode-an-encoded-base64-image-in-c-sharp-in-objective-c)

NSString *jsonImage = [jsonData objectForKey@"image"];
NSData   *data      = [NSData dataWithBase64EncodedString:jsonImage];

Then init your image with that data.

If you're using an NSArrayController to manage your core data, create a value transformer that returns an image.

Create a subclass of NSValueTransformer and name it whatever you'd like. In the implementation, add:

+(Class)transformedValueClass {
    return [NSImage class];
}
-(id)transformedValue:(id)value {
    if (value == nil) {
        return nil;
    } else {
        NSData *data = [NSData dataWithBase64EncodedString:value]; //might be [value stringValue]
        return [[NSImage alloc] initWithData:data];
    }
}

Then in interface builder where you've set the binding on the image, just set the Value Transformer to the class you made.

Answer 2

You didn't define what exactly is your problem.

To load NSImage from NSData see Apple docs and initWithData:.

---

Let's say You have such core data object:

@class MyObject : NSManagedObject

@property NSData *imageData;

@end 

and it's implementation:

@implementation MyObject

@dynamic imageData; 

@end

Now, add to it a new property:

-(NSImage *)bindableImage {
    [self willAccessValueForKey:@"bindableImage"];
    NSImage *myImage = [[NSImage alloc] initWithData:[self imageData]];
    [self didAccessValueForKey:@"bindableImage"];
    return myImage;
}

also, inform bindings what changes when imageData property has been changed:

+ (NSSet *)keyPathsForValuesAffectingImageData {
    return [NSSet setWithObjects:@"bindableImage", nil];
}

That's it. I think, it should work, but I didn't try :)

---

I forgot about Base64 - check another answer.