iOS Render UIImage to PDF and merging PDF files

Some code samples for working with PDF. Let’s try to generate 1000 images and render to PDF file. For this, we need a method for generating a random color and a method for creating UIImage from UIColor.

A random color:

- (UIColor *)randomColor
{
    CGFloat hue = (arc4random() % 256 / 256.0);
    CGFloat saturation = (arc4random() % 128 / 256.0) + 0.5;
    CGFloat brightness = (arc4random() % 128 / 256.0 ) + 0.5;
    return [UIColor colorWithHue:hue saturation:saturation brightness:brightness alpha:1];
}

And UIImage from UIColor:

- (UIImage *)imageFromColor:(UIColor *)color
{
    CGRect rect = CGRectMake(0, 0, 1024, 1024);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, rect);
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return image;
}

And now we can render random images to PDF file.

UIGraphicsBeginPDFContextToFile(filename, CGRectMake(0, 0, 1024, 1024), nil);

for (NSInteger i = 0; i < 1000; ++i) {
    UIImage *image = [self imageFromColor:[self randomColor]];

    @autoreleasepool {
        UIGraphicsBeginPDFPage();
        [image drawAtPoint:CGPointZero];
    }
}

UIGraphicsEndPDFContext();

Attention! Necessarily use @autoreleasepool, otherwise, you will have memory leaks.

Also, I would like to provide some sample for generating PDF files and merging these files. It’s also simple.

NSMutableArray *pdfURLs = [NSMutableArray array];

for (NSInteger i = 0; i < 1000; ++i) {
    NSString *pdfFile = [NSString stringWithFormat:@”%@_%@”, filename, @(i)];
    UIImage *imageToRender = [self imageFromColor:[self randomColor]];
  
    @autoreleasepool {
        UIGraphicsBeginPDFContextToFile(pdfFile, CGRectMake(0, 0, 1024, 1024), nil);
        UIGraphicsBeginPDFPage();
        [imageToRender drawAtPoint:CGPointZero];
        UIGraphicsEndPDFContext();
    }

    [pdfURLs addObject:[NSURL fileURLWithPath:pdfFile]];
}

[self combinePDFURLs:pdfURLs writeToURL:[NSURL fileURLWithPath:filename]];

for (NSURL *pdfUrl in pdfURLs) {
    [[NSFileManager defaultManager] removeItemAtURL:pdfUrl error:nil];
}

And of course, implementation of combinePDFURLs method, see below:

- (void)combinePDFURLs:(NSArray *)PDFURLs writeToURL:(NSURL *)URL
{
    CGContextRef context = CGPDFContextCreateWithURL((__bridge CFURLRef)URL, NULL, NULL);

    for (NSURL *PDFURL in PDFURLs) {
        CGPDFDocumentRef document = CGPDFDocumentCreateWithURL((__bridge CFURLRef)PDFURL); 
        size_t numberOfPages = CGPDFDocumentGetNumberOfPages(document);

        for (size_t pageNumber = 1; pageNumber <= numberOfPages; ++pageNumber) {
            CGPDFPageRef page = CGPDFDocumentGetPage(document, pageNumber);
            CGRect mediaBox = CGPDFPageGetBoxRect(page, kCGPDFMediaBox);
            CGContextBeginPage(context, &mediaBox);
            CGContextDrawPDFPage(context, page);
            CGContextEndPage(context);
        }

        CGPDFDocumentRelease(document);
    }

    CGPDFContextClose(context);
    CGContextRelease(context);
}

And the result:

Happy coding!