Objective C: How to convert CGImageRef to UIImageView? - objective-c

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!

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.

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;
}

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")
}
}