showing a pdf in uiwebview on ios9 sometimes scrolling is stuck

问题

I'm working on an ios app written in swift, xcode7

A view has a UIWebView on it.

using loadRequest(NSURLRequest) we load a pdf file from disk. This works fine, but sometimes the pdf file cannot be scrolled past the first page or what you see first on the screen. I can't pinpoint what causes the not-scrolling as sometimes I open the same file again and then it scrolls.

Trying to scroll when it doesn't want to bounces the bottom part of the screen and you can see there is another page, but you can't scroll it into view.

The UIScrollView contained inside the UIWebView (this is the default) knows there are more pages, because it shows "1 of 3" on screen.

The UIWebView

• has 'scales page to fit' checked
• has 'user interaction enabled' checked
• has 'multiple touch' NOT checked
• has 'autoresize subviews' checked
• has mode 'Scale To Fill'

I have tried the following:

• checking if the scrollview is not larger than the screen by placing a border around it: no, it fits on screen and is as large as you would expect
• setting the internal UIScrollView.scollEnabled to true in code

In the application, when showing the UIWebview, it is resized on screen by collapsing an element above it, but I have tested this with fixed heights and it doesn't change anything.

When I call flashScrollIndicators() on the internal UIScrollView, this is consistent with the scrolling or non-scrolling. If you see the scrollbar flash, then scrolling is possible. If not, then you can't scroll past the first page.

Any other ideas I can try?

回答1:

This sounds like a weird UIWebView problem. Two additional things you can check :

• Is the issue resolved after you rotate? (had this happen to me once)

• If you call flashScrollIndicators on the internal UIScrollView and it's not responding. Is the internal UIScrollView a nil object?

Another solution is to try and use WKWebView. It might resolve the issue. Just be sure to only use it in the last versions of iOS.

You can also step down a layer and implement it with CoreGraphics since you have the PDF on the device itself and not on the web (official docs). There is probably a good CocoaPod or Carthage framework you can use for this.

回答2:

The underlying problem was the fact that before loading a new pdf, the UIWebView was cleared each time by loading 'about:blank', which is the most suggested solution to clear the webview. However, when working with pdfs with different page sizes and different number of pages, this seems to mess with the built-in scrollview.

The solution in this case was to create a kind of 'blank' pdf with a single page (and maybe an application logo in it to distinguish it clearly for the user) and instead of loading about:blank, load this pdf instead before showing the webview to the user and while waiting for the real pdf to download to the device.

来源：https://stackoverflow.com/questions/35579248/showing-a-pdf-in-uiwebview-on-ios9-sometimes-scrolling-is-stuck