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

Question

It is possible to use JavaScript to set the pixel y-offset of a UIWebView, e.g.:

[webView stringByEvaluatingJavaScriptFromString:[NSString stringWithFormat:@"scrollTo(0, %d)", offset]];

So is there a way to get:

1. The pixel height of an individual page of a PDF within the web view?
2. The size of the gap between pages?

Is this information available from the UIWebView or can it be calculated through alternative means?

I'm thinking that if I have the number of pages (via CGPDFDocumentGetNumberOfPages), the pixel height gap between pages, or the pixel height of an individual page, I can calculate the offset to use with the JavaScript call. Then I just wire up a UIButton or UISlider to move between pages.

---

EDIT I

I have a solution, but it uses UIWebDocumentView, a private subview of UIWebView.

I create a view controller called PDFViewerViewController, which is a subclass of WebViewerViewController, which itself is a view controller that contains a UIToolbar, a UIWebView, and conforms to the UIWebViewDelegate protocol.

My PDFViewerViewController calculates some information about the enclosing web view and the PDF data, after the web view delegate method -webViewDidFinishLoad: gets called.

This information is used to calculate an approximate per-page offset that gets fed to the web view via JavaScript.

PDFViewerViewController.h

#import <UIKit/UIKit.h>
#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

PDFViewerViewController.m

#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)]];
}

Some observations

1. 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.

2. The self.currentPage 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.

3. This solution uses UIWebDocumentView, which is private and may likely cause app rejection.

I think I'll file a feature enhancement request with Apple.

Has anyone built a non-UIWebView-based PDF viewer (with source code)?

Answer 1

I think that you'll have to load and display the PDF yourself using the PDF APIs rather than UIWebView. Here is an possible idea of how to simulate snapping scrolling to rectangular grid boundaries which may help you make the experience more like a UIWebView for your users.

http://stackoverflow.com/questions/1907297/iphone-sdk-cocoa-touch-pass-touches-down-from-parent-uiview-to-child-uiscrollvi/1915882#1915882

Answer 2

I have seen your edit in question. Has anyone built a non-UIWebView-based PDF viewer (with source code)?

See my question.

http://stackoverflow.com/questions/2362393/reading-pdf-files-as-string-through-iphone-application

It has functionality to display each pdf page in an image view. user can easily change pages. But the missing points are as follows.

• user can not make any selection - as it is not text but an image
• user can't find any text.
• user can not zoom ( oh yes - you can put image view in scroll view for zooming functionality )