Rendering PDF in Apple TV tvOS

问题:

I am working on an addition to my tvOS app that would allow viewing of PDFs stored in the app. However, without UIWebView, I'm at a loss on how to do this. I've asked question in other places, and get greeted with a link to a wordy and helpless document from Apple about the APIs that can be used, and even here it has been referenced (CGPDFPage) but no real guide on how to implement this. Has anyone successfully done this on tvOS, and if so, would you help me get started in this process?

回答1:

Below is some code that I wrote and tested in tvOS. Note that this is in Objective-c.

I've created two functions to do the job, and one helper function to display the PDF images in a UIScrollView. The first one will open the PDF document from a URL. A web URL was used. A local file could also be used in this sample.

There is also a helper function to open a document from a local file.

The second function renders the PDF document to a context. I chose to display the context by creating an image from it. There are other ways of handling the context too.

Opening the document is fairly straight forward, so there are no comments in the code for that. Rendering the document is slightly more involved, and so there are comments explaining that function.

The complete application is below.

- (CGPDFDocumentRef)openPDFLocal:(NSString *)pdfURL {
    NSURL* NSUrl = [NSURL fileURLWithPath:pdfURL];

    return [self openPDF:NSUrl];
}

- (CGPDFDocumentRef)openPDFURL:(NSString *)pdfURL {
    NSURL* NSUrl= [NSURL URLWithString:pdfURL];

    return [self openPDF:NSUrl];
}

- (CGPDFDocumentRef)openPDF:(NSURL*)NSUrl {
    CFURLRef url = (CFURLRef)CFBridgingRetain(NSUrl);

    CGPDFDocumentRef myDocument;
    myDocument = CGPDFDocumentCreateWithURL(url);
    if (myDocument == NULL) {
        NSLog(@"can't open %@", NSUrl);
        CFRelease (url);
        return nil;
    }
    CFRelease (url);

    if (CGPDFDocumentGetNumberOfPages(myDocument) == 0) {
        CGPDFDocumentRelease(myDocument);
        return nil;
    }

    return myDocument;
}
- (void)drawDocument:(CGPDFDocumentRef)pdfDocument
{
    // Get the total number of pages for the whole PDF document
    int  totalPages= (int)CGPDFDocumentGetNumberOfPages(pdfDocument);
    NSMutableArray *pageImages = [[NSMutableArray alloc] init];

    // Iterate through the pages and add each page image to an array
    for (int i = 1; i <= totalPages; i++) {
        // Get the first page of the PDF document
        CGPDFPageRef page = CGPDFDocumentGetPage(pdfDocument, i);
        CGRect pageRect = CGPDFPageGetBoxRect(page, kCGPDFMediaBox);

        // Begin the image context with the page size
        // Also get the grapgics context that we will draw to
        UIGraphicsBeginImageContext(pageRect.size);
        CGContextRef context = UIGraphicsGetCurrentContext();

        // Rotate the page, so it displays correctly
        CGContextTranslateCTM(context, 0.0, pageRect.size.height);
        CGContextScaleCTM(context, 1.0, -1.0);
        CGContextConcatCTM(context, CGPDFPageGetDrawingTransform(page, kCGPDFMediaBox, pageRect, 0, true));

        // Draw to the graphics context
        CGContextDrawPDFPage(context, page);

        // Get an image of the graphics context
        UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        [pageImages addObject:image];
    }
    // Set the image of the PDF to the current view
    [self addImagesToScrollView:pageImages];
}

-(void)addImagesToScrollView:(NSMutableArray*)imageArray {
    int heigth = 0;
    for (UIImage *image in imageArray) {
        UIImageView *imgView = [[UIImageView alloc] initWithImage:image];
        imgView.frame=CGRectMake(0, heigth, imgView.frame.size.width, imgView.frame.size.height);
        [_scrollView addSubview:imgView];
        heigth += imgView.frame.size.height;
    }
}

And to tie it all together, you can do this:

CGPDFDocumentRef pdfDocument = [self openPDFURL:@"http://www.guardiansuk.com/uploads/accreditation/10testing.pdf"];
[self drawDocument:pdfDocument];

Note that I'm using a random PDF that was available for free on the web. I ran into some problems with https URLs, but I'm sure this can be resolved, and it's not actually related to the PDF opening question.

回答2:

The tvOS documentation contains a section on creating, viewing and transforming PDF documents so I think it contains the functionality you need.

There’s lots of example code on that page, but here’s some code I use on iOS for the same purpose. It should work on tvOS, but I don’t have a way to test it:

func imageForPDF(URL: NSURL, pageNumber: Int, imageWidth: CGFloat) -> UIImage {
    let document = CGPDFDocumentCreateWithURL(URL)
    let page = CGPDFDocumentGetPage(document, pageNumber)
    var pageRect = CGPDFPageGetBoxRect(page, .MediaBox)
    let scale = imageWidth / pageRect.size.width
    pageRect.size = CGSizeMake(pageRect.size.width * scale, pageRect.size.height * scale)
    pageRect.origin = CGPointZero

    UIGraphicsBeginImageContext(pageRect.size)
    let ctx = UIGraphicsGetCurrentContext()
    CGContextSetRGBFillColor(ctx, 1.0, 1.0, 1.0, 1.0) // White background
    CGContextFillRect(ctx, pageRect)
    CGContextSaveGState(ctx)

    // Rotate the PDF so that it’s the right way around
    CGContextTranslateCTM(ctx, 0.0, pageRect.size.height)
    CGContextScaleCTM(ctx, 1.0, -1.0)
    CGContextConcatCTM(ctx, CGPDFPageGetDrawingTransform(page, .MediaBox, pageRect, 0, true))

    CGContextDrawPDFPage(ctx, page)
    CGContextRestoreGState(ctx)

    let image = UIGraphicsGetImageFromCurrentImageContext()
    UIGraphicsEndImageContext()

    return image
}