How to check pixel color of a UIView or a UIImage?

Question

I am trying to check if an entire UIView is filled with one color. I managed to get a screenshot of the UIView using the following block of code:

UIImage *image = [self imageFromView];
NSFileManager *fileManager = [NSFileManager defaultManager];
NSData *myImageData = UIImagePNGRepresentation(image);
[fileManager createFileAtPath:@"/Users/{username}/Desktop/myimage.png" contents:myImageData attributes:nil];
[imageData writeToFile:@"/testImage.jpg" atomically:YES];

The method implementation for imageFromView is the following:

- (UIImage*)imageFromView{  
UIImage *bitmapImage;
UIGraphicsBeginImageContext(self.bounds.size);
[self.layer renderInContext:UIGraphicsGetCurrentContext()];
bitmapImage = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
return bitmapImage; 
}

So from what I understand, I now have a bitmap image of the UIView. How do I access each pixel of the UIImage and check to verify it is in fact one color (i.e. UIColor blackColor)?

Answer 1

If you go back to that answer, the following (untested) snippet should get you started:

- (BOOL) checkForUniqueColor: (UIImage *) image {
    CGImageInspection * inspector = 
        [CGImageInspection imageInspectionWithCGImage: [image CGImage]] ;

    for (CGFloat x = 0 ; x < image.size.width ; x += 1.0f) {
        for (CGFloat y = 0 ; y < image.size.height ; y += 1.0f) {
            CGFloat red ;
            CGFloat green ;
            CGFloat blue ;
            CGFloat alpha ;

            [inspector colorAt: (CGPoint) {x, y}
                           red: &red
                         green: &green
                          blue: &blue
                         alpha: &alpha
            ] ;

            if (red == ... && green == ... && blue == ... && alpha == ...) {

            }
        }
    }
}