Image of the first pdf page ios sdk

Question

Do you know how to save into a UIImageView the first page of a pdf file? I have to create the preview for the pdf. Do you have any idea?

Thanks for help Nicco

Answer 1

As part of a project I was working on, I modified inwit's code to be used with variables in their calls. I figured I would post them here to help anyone who was looking for a similar solution:

To call them:

//Assume all your PDFs you want to create thumbnails for are in an array. This method saves the paths to all PDFs in your main bundle as NSStrings.
_pdfs = [[NSBundle mainBundle] pathsForResourcesOfType:@"pdf" inDirectory:nil];

//To be called in the cellForItemAtIndexPath method or a similar method where you want to create a thumbnail for the image:
NSString *loc = [_pdfs objectAtIndex:indexPath.row];    
UIImage *cellImage = [self buildThumbnailImage:MyGetPDFDocumentRef(loc)];

The method and C function:

- (UIImage *)buildThumbnailImage:(CGPDFDocumentRef)pdfDocument
{
    BOOL hasRetinaDisplay = FALSE;  // by default
    CGFloat pixelsPerPoint = 1.0;  // by default (pixelsPerPoint is just the "scale" property of the screen)

    if ([UIScreen instancesRespondToSelector:@selector(scale)])  // the "scale" property is only present in iOS 4.0 and later
    {
        // we are running iOS 4.0 or later, so we may be on a Retina display;  we need to check further...
        if ((pixelsPerPoint = [[UIScreen mainScreen] scale]) == 1.0)
            hasRetinaDisplay = FALSE;
        else
            hasRetinaDisplay = TRUE;
    }
    else
    {
        // we are NOT running iOS 4.0 or later, so we can be sure that we are NOT on a Retina display
        pixelsPerPoint = 1.0;
        hasRetinaDisplay = FALSE;
    }

    size_t imageWidth = 320;  // width of thumbnail in points
    size_t imageHeight = 460;  // height of thumbnail in points

    if (hasRetinaDisplay)
    {
        imageWidth *= pixelsPerPoint;
        imageHeight *= pixelsPerPoint;
    }

    size_t bytesPerPixel = 4;  // RGBA
    size_t bitsPerComponent = 8;
    size_t bytesPerRow = bytesPerPixel * imageWidth;

    void *bitmapData = malloc(imageWidth * imageHeight * bytesPerPixel);

    // in the event that we were unable to mallocate the heap memory for the bitmap,
    // we just abort and preemptively return nil:
    if (bitmapData == NULL)
        return nil;

    // remember to zero the buffer before handing it off to the bitmap context:
    bzero(bitmapData, imageWidth * imageHeight * bytesPerPixel);

    CGContextRef theContext = CGBitmapContextCreate(bitmapData, imageWidth, imageHeight, bitsPerComponent, bytesPerRow,
                                                    CGColorSpaceCreateDeviceRGB(), kCGImageAlphaPremultipliedLast);

    //CGPDFDocumentRef pdfDocument = MyGetPDFDocumentRef();  // NOTE: you will need to modify this line to supply the CGPDFDocumentRef for your file here...
    CGPDFPageRef pdfPage = CGPDFDocumentGetPage(pdfDocument, 1);  // get the first page for your thumbnail

    CGAffineTransform shrinkingTransform =
    CGPDFPageGetDrawingTransform(pdfPage, kCGPDFMediaBox, CGRectMake(0, 0, imageWidth, imageHeight), 0, YES);

    CGContextConcatCTM(theContext, shrinkingTransform);

    CGContextDrawPDFPage(theContext, pdfPage);  // draw the pdfPage into the bitmap context
    CGPDFDocumentRelease(pdfDocument);

    //
    // create the CGImageRef (and thence the UIImage) from the context (with its bitmap of the pdf page):
    //
    CGImageRef theCGImageRef = CGBitmapContextCreateImage(theContext);
    free(CGBitmapContextGetData(theContext));  // this frees the bitmapData we malloc'ed earlier
    CGContextRelease(theContext);

    UIImage *theUIImage;

    // CAUTION: the method imageWithCGImage:scale:orientation: only exists on iOS 4.0 or later!!!
    if ([UIImage respondsToSelector:@selector(imageWithCGImage:scale:orientation:)])
    {
        theUIImage = [UIImage imageWithCGImage:theCGImageRef scale:pixelsPerPoint orientation:UIImageOrientationUp];
    }
    else
    {
        theUIImage = [UIImage imageWithCGImage:theCGImageRef];
    }

    CFRelease(theCGImageRef);
    return theUIImage;
}


CGPDFDocumentRef MyGetPDFDocumentRef(NSString *inputPDFFile)
{
    //NSString *inputPDFFile = [[[NSBundle mainBundle] bundlePath] stringByAppendingPathComponent:@"test.pdf"];

    const char *inputPDFFileAsCString = [inputPDFFile cStringUsingEncoding:NSASCIIStringEncoding];
    //NSLog(@"expecting pdf file to exist at this pathname: \"%s\"", inputPDFFileAsCString);

    CFStringRef path = CFStringCreateWithCString(NULL, inputPDFFileAsCString, kCFStringEncodingUTF8);

    CFURLRef url = CFURLCreateWithFileSystemPath(NULL, path, kCFURLPOSIXPathStyle, 0);
    CFRelease (path);

    CGPDFDocumentRef document = CGPDFDocumentCreateWithURL(url);
    CFRelease(url);

    if (CGPDFDocumentGetNumberOfPages(document) == 0)
    {
        printf("Warning: No pages in pdf file \"%s\" or pdf file does not exist at this path\n", inputPDFFileAsCString);
        return NULL;
    }

    return document;
}