Objective C: How to convert CGImageRef to UIImageView?

Question

I'm using the XZINGObjC framework to create an EAN-Barcode-Image. Following the documentation, I'm doing it like

 //in viewDidAppear

 //XZING: create Matrix
 NSString* eanString = @"1234567890123";  //sth. like that
 ZXBitMatrix* result = [writer encode:eanString
                              format:kBarcodeFormatEan13
                               width:500
                              height:500
                               error:&error];
if (result) {
      //XZING: convert matrix to CGImageRef
      CGImageRef imageRef = [[ZXImage imageWithMatrix:result] cgimage]; 

      //CRASHLINE HERE!! (this is NOT in the XZING documentation, but i cannot figure out the issue!)
      UIImage* uiImage = [[UIImage alloc] initWithCGImage:imageRef];  //<--CRASH: EXC_BAD_ACCESS

      if(image != nil){
          //assigning image to ui
          self.barCodeImageView.image = uiImage;   
      }

It works, if I step through this code using breakpoints! However, I think at some point an Image is not ready for use?! But I cannot find the reason.

What I tried:

• using imageRef and uiImage as local variables (EXC_BAD_ACCESS CRASH)
• tried that operation in a background thread (EXC_BAD_ACCESS CRASH)

Same here, every solution worked if I used breakpoints and stepped line by line through the code. What is my mistake here? Any ideas? Thanks in advance!

Bard

check this reference link. may be you will get some help. – Truman

If you are stepping through, what is the contents of imageRef? – Sacks

@pawan: thanks, i found that but it didnt solve my issue @Sulthan: 'imageRef' is not nil if you mean that... it works like it should if I use breakpoints. So something is already released or not ready to use, but I dont know what exactely – Bard

Answer 1

After some try and error programming, I could fix the issue by replacing the following lines

  CGImageRef imageRef = [[ZXImage imageWithMatrix:result] cgimage]; 
  UIImage* uiImage = [[UIImage alloc] initWithCGImage:imageRef];  //<--CRASH

with

 UIImage* uiImage = [[UIImage alloc] initWithCGImage:[[ZXImage imageWithMatrix:result] cgimage]];

Still, I don't know why?! I'm pretty sure something isn't hold in the memory or maybe the CGImageRef isn't ready if I try to convert it to UIImage.

Bard

See the link in pawan’s comment. I believe it has the right answer, which has to do with ARC and ivars. – Tinctorial

Answer 2

Problem is with in [ZXImage imageWithMatrix:result], it is creating CGImage and before assigning it to ZXImage which will increase its retain count it is releasing the CGImage by CFRelease.

To fix this issue, replace + (ZXImage *)imageWithMatrix:(ZXBitMatrix *)matrix method with below implementation.

+ (ZXImage *)imageWithMatrix:(ZXBitMatrix *)matrix {
    int width = matrix.width;
    int height = matrix.height;
    int8_t *bytes = (int8_t *)malloc(width * height * 4);
    for(int y = 0; y < height; y++) {
        for(int x = 0; x < width; x++) {
            BOOL bit = [matrix getX:x y:y];
            int8_t intensity = bit ? 0 : 255;
            for(int i = 0; i < 3; i++) {
                bytes[y * width * 4 + x * 4 + i] = intensity;
            }
            bytes[y * width * 4 + x * 4 + 3] = 255;
        }
    }

    CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
    CGContextRef c = CGBitmapContextCreate(bytes, width, height, 8, 4 * width, colorSpace, kCGBitmapAlphaInfoMask & kCGImageAlphaPremultipliedLast);

    CGImageRef image = CGBitmapContextCreateImage(c);


    ZXImage *zxImage = [[ZXImage alloc] initWithCGImageRef:image];
    CFRelease(colorSpace);
    CFAutorelease(image);
    CFRelease(c);
    free(bytes);
    return zxImage;
}

Gemeinschaft

Answer 3

For people writing Swift, I hit the same problem that longilong described. The answer was in the ZXingObjC objective C example projects. Remember: this is for generating a barcode only.

internal func encodeBarcode(){
    let writer : ZXMultiFormatWriter! = ZXMultiFormatWriter()
    var result: ZXBitMatrix!
    let hint: ZXEncodeHints! = ZXEncodeHints()

    do {
        hint.margin = 0
        result = try writer.encode("Example String", format: kBarcodeFormatAztec, width: 500, height: 500, hints: hint)

        **let rawBarcode: ZXImage = ZXImage(matrix: result)
        barcodeUIImage.image = UIImage(CGImage: rawBarcode.cgimage)**

    } catch {
        print("failed to generate barcode")
    }
}

Fonville