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POIs there a way to programmatically scroll to a PDF page within a UIWebView?
 

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  1. POIs there a way to programmatically scroll to a PDF page within a UIWebView?
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    <p>It is possible to use JavaScript to set the pixel y-offset of a <code>UIWebView</code>, e.g.:</p> <pre><code>[webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"scrollTo(0, %d)", offset]]; </code></pre> <p>So is there a way to get:</p> <ol> <li>The pixel height of an individual page of a PDF within the web view?</li> <li>The size of the gap between pages?</li> </ol> <p>Is this information available from the <code>UIWebView</code> or can it be calculated through alternative means?</p> <p>I'm thinking that if I have the number of pages (via <a href="http://developer.apple.com/mac/library/DOCUMENTATION/GraphicsImaging/Reference/CGPDFDocument/Reference/reference.html#//apple_ref/doc/uid/TP30000958-CH1g-F17191" rel="noreferrer"><code>CGPDFDocumentGetNumberOfPages</code></a>), the pixel height gap between pages, or the pixel height of an individual page, I can calculate the <code>offset</code> to use with the JavaScript call. Then I just wire up a <code>UIButton</code> or <code>UISlider</code> to move between pages.</p> <hr> <p><strong>EDIT I</strong></p> <p>I have a solution, but it uses <code>UIWebDocumentView</code>, a private subview of <code>UIWebView</code>.</p> <p>I create a view controller called <code>PDFViewerViewController</code>, which is a subclass of <code>WebViewerViewController</code>, which itself is a view controller that contains a <code>UIToolbar</code>, a <code>UIWebView</code>, and conforms to the <code>UIWebViewDelegate</code> protocol.</p> <p>My <code>PDFViewerViewController</code> calculates some information about the enclosing web view and the PDF data, after the web view delegate method <code>-webViewDidFinishLoad:</code> gets called. </p> <p>This information is used to calculate an approximate per-page offset that gets fed to the web view via JavaScript.</p> <p><strong>PDFViewerViewController.h</strong></p> <pre><code>#import &lt;UIKit/UIKit.h&gt; #import "WebViewerViewController.h" @interface UIWebDocumentView : NSObject {} @end @interface PDFViewerViewController : WebViewerViewController { NSUInteger offset; NSUInteger currentPage; NSUInteger documentPages; CGFloat documentHeight; CGFloat pageHeight; } @property (assign) NSUInteger offset; @property (assign) NSUInteger currentPage; @property (assign) NSUInteger documentPages; @property (assign) CGFloat documentHeight; @property (assign) CGFloat pageHeight; @end </code></pre> <p><strong>PDFViewerViewController.m</strong></p> <pre><code>#import "PDFViewerViewController.h" @implementation PDFViewerViewController @synthesize offset; @synthesize currentPage; @synthesize documentPages; @synthesize documentHeight; @synthesize pageHeight; - (void) viewDidLoad { [super viewDidLoad]; UIBarButtonItem *_leftArrow = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"ArrowLeft.png"] style:UIBarButtonItemStylePlain target:self action:@selector(leftArrow:)]; UIBarButtonItem *_flexibleSpace = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemFlexibleSpace target:self action:nil]; UIBarButtonItem *_rightArrow = [[UIBarButtonItem alloc] initWithImage:[UIImage imageNamed:@"ArrowRight.png"] style:UIBarButtonItemStylePlain target:self action:@selector(rightArrow:)]; [[super.viewerToolbarView toolbar] setItems:[NSArray arrayWithObjects:_leftArrow, _flexibleSpace, _rightArrow, nil]]; [_leftArrow release]; [_flexibleSpace release]; [_rightArrow release]; self.currentPage = 0; } - (void) webViewDidFinishLoad:(UIWebView *)_webView { for (UIView *_subview in [[[_webView subviews] objectAtIndex:0] subviews]) { if ([_subview isKindOfClass:[UIWebDocumentView class]]) { self.documentHeight = _subview.bounds.size.height; } } CGPDFDocumentRef pdfDocument = CGPDFDocumentCreateWithURL((CFURLRef)baseURL); self.documentPages = CGPDFDocumentGetNumberOfPages(pdfDocument); CGPDFDocumentRelease(pdfDocument); self.pageHeight = (self.documentHeight + (10 * self.documentPages)) / self.documentPages; self.currentPage = 1; self.offset = 0; } - (void) leftArrow:(id)_param { if (self.currentPage == 1) return; self.offset -= (NSUInteger)self.pageHeight; self.currentPage--; [webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"scrollTo(0, %d)", (self.offset * 2)]]; } - (void) rightArrow:(id)_param { if (self.currentPage == self.documentPages) return; self.offset += (NSUInteger)self.pageHeight; self.currentPage++; [webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"scrollTo(0, %d)", (self.offset * 2)]]; } </code></pre> <p><strong>Some observations</strong></p> <ol> <li><p>The offset calculation isn't page-perfect. If the PDF document isn't 8.5 x 11 (e.g. A4) then the offset error gets worse more quickly.</p></li> <li><p>The <code>self.currentPage</code> property doesn't get updated when scrolling through the web view by way of touch-drag. One might drag a few pages, and then touching the left or right arrow on the toolbar will cause the offset to unexpectedly move to a previous page.</p></li> <li><p>This solution uses <code>UIWebDocumentView</code>, which is private and may likely cause app rejection.</p></li> </ol> <p>I think I'll file a feature enhancement request with Apple. </p> <p>Has anyone built a non-<code>UIWebView</code>-based PDF viewer (with source code)?</p>
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    1. COIf that doesn't work, did you try putting the PDF in an iframe (standard frames discouraged by iPhone docs but iframes may be okay) and calling a JavaScript in the parent HTML document?
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    2. COI don't think the number of pages is available from the web view. Your suggestion seems okay. Try setting scalesPagesToFit=YES then page height should be browser view/frame height.
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    3. COI suppose you're scuppered when the user changes the zoom level! Tricky. Did you try inspecting the DOM model when the PDF is embedded in an iframe - though this might start to move towards non-public API use perhaps?
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