为下载 PDF 时添加完成处理程序

Question

我的应用程序使用以下代码在 tvOS 应用程序中显示 PDF：

 CGPDFDocumentRef pdfDocument2 = [self openPDF:[NSURL URLWithString:@"https://pdfislistedhere"]];
        [self drawDocument:pdfDocument2];

但是，它似乎尝试绘制得太快了。有没有办法能够将完成处理程序添加到下面列出的 CGPDFDocumentRef 代码中？这是我得到帮助的代码，无法弄清楚是否有一个好的方法让它等待运行 drawDocument:pdfDocument 直到实际下载 PDF 之后？截至目前，它什么都不做，但会像成功一样运行所有检查和日志。

- (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
{   NSLog(@"draw document");
    theImageView.hidden = YES;
    // Get the total number of pages for the whole PDF document
    int  totalPages= (int)CGPDFDocumentGetNumberOfPages(pdfDocument);

    if ([[self.arrayOfVerses firstObject] isEqualToString:@"allverses"]) {
        NSLog(@"draw document all verses %d", totalPages);
        self.pages = totalPages;
        self.subtractingPages = totalPages - 1;

        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];
    }
    else {
        self.pages = [self.arrayOfVerses count];
        self.subtractingPages = self.pages - 1;

        NSLog (@"total pages %ld", (long)self.pages);
        NSMutableArray *pageImages = [[NSMutableArray alloc] init];
        
        
        [pageImages removeAllObjects];
        
        //Getting slide numbers to be used
        NSString *text = self.selectedCountry;
        NSString *substring = nil;
        
        NSRange parenRng = [text rangeOfString: @"(?<=\\().*?(?=\\))" options: NSRegularExpressionSearch];
        
        if ( parenRng.location != NSNotFound ) {
            substring = [text substringWithRange:parenRng];
            NSLog(@"Substring %@", substring);
        }
        
        
        // 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
            
            
            NSPredicate *valuePredicate=[NSPredicate predicateWithFormat:@"self.intValue == %d",i];
            
            if ([[self.arrayOfVerses filteredArrayUsingPredicate:valuePredicate] count]!=0) {
                // FOUND
                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];
            }
            
            else  {
                //NOT FOUND
            }
            
        }
        // Set the image of the PDF to the current view
        [self addImagesToScrollView:pageImages];
    }
}