Getting NSData from UIImage object that contains CGImage

Question

In order to upload an image file to my server, I need to get it's NSData. I am having trouble doing this right now, because my UIImage contains a CGImage.

Let me show you how I am doing things. When a user takes a photo, this is what I do with the captured photo:

NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer];


UIImage *image = [[UIImage alloc]initWithData:imageData];


   _subLayer = [CALayer layer];


      image = [self selfieCorrection:image];


      image = [self rotate:image andOrientation:image.imageOrientation];


          CGRect cropRectFinal = CGRectMake(cropRect.origin.x, 140, cropRect.size.width, cropRect.size.height);

          CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], cropRectFinal);


_subLayer.contents = (id)[UIImage imageWithCGImage:imageRef].CGImage;

In the above code, I create a UIImage, and initialize it with the imageData object. I also create a layer object called _subLayer that will display the final image on the screen. The image's orientation is then rotated and corrected, and then I setup a CGRect to crop the part of the image I want to keep.

The most important part are the last 2 statements. I create a CGImageRef called imageRef using the original UIImage. Then, in the last statement, I set the contents property of _subLayer to equal my final image.

A little further down in this same view controller, inside of an IBAction I have the following statement which helps me pass the image to my next view controller: sendFriendsVC.finalPhotoToSend = _subLayer.contents;

finalPhotoToSend is a property that I have setup in the header file of my next view controller like this:

@property (nonatomic, retain) UIImage *finalPhotoToSend;

The data is successfully passed when I segue to the next view controller, but when I NSLog finalPhotoToSend, even though it is a UIImage, it prints as this to the console:

<CGImage 0x1563dac0>

In order to upload photos to my backend server service, it requires me to create an object using NSData. I have tried using these 2 methods to get the NSData out of the finalPhotoToSend object:

NSData *imageData = UIImageJPEGRepresentation(finalPhotoToSend, 0.7);

and

NSData *imageData = UIImagePNGRepresentation(finalPhotoToSend);

But those always give me the following error in xcode:

NSInvalidArgumentException', reason: '-[__NSCFType CGImage]: unrecognized selector sent to instance

I am not sure what to do. Is there a different method I should be using to get NSData out of my UIImage since it is technically holding a CGImage? Should I be doing something differently before I even pass the data to my next view controller?

Edit for Michael:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:self {


    if ([segue.identifier isEqualToString:@"mediaCaptureToSendToFriendsSegue"]) {


    SendToFriendsViewController *sendFriendsVC = segue.destinationViewController;


        sendFriendsVC.finalPhotoToSend = _subLayer.contents;


    }
}

Answer 1

Better answer:

You need to truly set a UIImage object (and not a CGImage pointer) to a property that you've declared to be a UIImage object.

Original:

if "finalPhotoToSend" is a property, you should be doing:

NSData *imageData = UIImageJPEGRepresentation(self.finalPhotoToSend, 0.7);

and not:

NSData *imageData = UIImageJPEGRepresentation(finalPhotoToSend, 0.7);

Answer 2

I just figured it out. Here's what I ended up using for the IBAction method implementation:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:self {


    if ([segue.identifier isEqualToString:@"mediaCaptureToSendToFriendsSegue"]) {


        SendToFriendsViewController *sendFriendsVC = segue.destinationViewController;


        UIImage* image2 = [UIImage imageWithCGImage:(__bridge CGImageRef)(_subLayer.contents)];

        sendFriendsVC.finalPhotoToSend = image2;


    }
}

I'm new to objective-c and not really entirely sure what the following statement is even doing:

UIImage* image2 = [UIImage imageWithCGImage:(__bridge CGImageRef)(_subLayer.contents)];

But xcode suggested it and it works. Now on the next view controller, the finalPhotoToSend object NSLogs as a UIImage instead of a CGImage.