Question

I have a UITableView, and in every cell there’s displayed a UIImage created from a pdf. But now the performance is very bad. Here’s my code I use to generate the UIImage from the PDF.

Creating CGPDFDocumentRef and UIImageView (in cellForRowAtIndexPath method):

...    
CFURLRef pdfURL = CFBundleCopyResourceURL(CFBundleGetMainBundle(), (CFStringRef)formula.icon, NULL, NULL);
CGPDFDocumentRef documentRef = CGPDFDocumentCreateWithURL((CFURLRef)pdfURL);
CFRelease(pdfURL);
UIImageView *imageView = [[UIImageView alloc] initWithImage:[self imageFromPDFWithDocumentRef:documentRef]];
...

Generate UIImage:

- (UIImage *)imageFromPDFWithDocumentRef:(CGPDFDocumentRef)documentRef {
    CGPDFPageRef pageRef = CGPDFDocumentGetPage(documentRef, 1);
    CGRect pageRect = CGPDFPageGetBoxRect(pageRef, kCGPDFCropBox);

    UIGraphicsBeginImageContext(pageRect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    CGContextTranslateCTM(context, CGRectGetMinX(pageRect),CGRectGetMaxY(pageRect));
    CGContextScaleCTM(context, 1, -1);  
    CGContextTranslateCTM(context, -(pageRect.origin.x), -(pageRect.origin.y));
    CGContextDrawPDFPage(context, pageRef);

    UIImage *finalImage = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    return finalImage;
} 

What can I do to increas the speed and keep the memory low?

Answer 1

Generating image from PDF for each cell in runtime seems like a huge performance hit.

You should try to consider maybe performing the actual rendering in the background thread and store the rendered result UIImages and populate them into the UITableView in runtime. This will at-least free up the UI thread and add responsiveness to application.

For the cells that are not yet rendered you can display a ‘loading’ message or add a ‘activity indicator’ spinner.