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WKWebView fails to load images and CSS using loadHTMLString(_, baseURL:)

Apple's recommendation:

In apps that run in iOS 8 and later, use the WKWebView class instead of using UIWebView.

Thus, I have replaced my good old UIWebView with a shiny new WKWebView. But what I thought to be an easy exercise (simply swapping the classes and replacing the delegate methods) turned out to be a real mess.

The Problem

When I load an HTML string using

loadHTMLString(String, baseURL: URL?)

the web view loads and renders the pure HTML but it doesn't load any images or CSS files referenced inside the htmlString.

This happens only on a real device!
In Simultor all referenced resources are loaded correctly.

Simulator Real Device

Example

I have defined a simple htmlString in my view controller class:

let imageName = "image.png"
let libraryURL: URL // The default Library URL
var htmlString: String {
 return "<html> ... <img src=\"\(imageName)\" /> ... </html>"
 // "..." represents more valid HTML code incl. header and body tags
}

The image is stored in the root Library folder so its URL is:

let imageURL = libraryURL.appendingPathComponent(imageName)

Now I load the htmlString into the web view:

webView.loadHTMLString(htmlString, baseURL: libraryURL)

and it doesn't load the image even though the baseURL is set correctly.

Ideas for a Solution

  1. Maybe WKWebView has a problem with resolving relative paths so my first idea was to use absolute paths inside the HTML string instead.
    → ❌ Doesn't work.

  2. Two answers to another SO post suggested that using
    loadFileURL(URL, allowingReadAccessTo: URL)
    instead of loadHTMLString(...) works in iOS 9+.
    → ✅ That works.

However, I cannot use solution 2 because my HTML files are encrypted and the decrypted files must not be stored on the disk.

Question

Is there any way to load local resources like images and styles using the WKWebView's

loadHTMLString(String, baseURL: URL?)

function? Or is still a bug in iOS 9+?

(I just cannot believe that Apple provides and recommends using a web view that cannot load any local web content from inside an HTML string?!)

Answer*

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  • Sounds like a smart work-around! Will try that. However, it really feels like dirty hacking in my case because I'll have to parse the HTML, find all image URLs, encode them as base64 data and replace the URL with the data. Commented Oct 6, 2016 at 19:20
  • yea, I can see that. In my case I already have the image that i want to get into the html so it was a bit cleaner. Commented Oct 6, 2016 at 19:31
  • I've tried base64 encoding the images and it still does not work. github.com/starkindustries/Print2PDFTest Commented Nov 29, 2018 at 14:01

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