SWIFT: How to load local images remote HTML - ios

Question

Currently I'm developing an app for Android and iOS. It is a simple webView which is calling a remote URL.
This works perfectly fine - but now I have a problem figuring out how to intercept the loading of images.
I'm trying to achieve the following:
* Load remote URL
* Intercept load and check for images
* If the image exists within the app (in a certain folder) load the local image, otherwise load the remote image from the server
On Android it is pretty easy:
public WebResourceResponse shouldInterceptRequest(WebView view, String url) {
try {
if( url.endsWith("png") ) {
return new WebResourceResponse("image/png", "ISO-8859-1", ctx.getAssets().open(url.substring(basepath.length())));
}
if( url.endsWith("jpg") ) {
return new WebResourceResponse("image/jpg", "ISO-8859-1", ctx.getAssets().open(url.substring(basepath.length())));
}
} catch (IOException e) {
}
return super.shouldInterceptRequest(view, url);
}
On iOS - especially SWIFT I haven't found a solution to it yet. So far this is what I have for my webView:
#IBOutlet var webView: UIWebView!
var urlpath = "http://stackoverflow.com"
func loadAddressURL(){
let requesturl = NSURL(string: urlpath!)
let request = NSURLRequest(URL: requesturl)
webView.loadRequest(request) }
override func viewDidLoad() {
super.viewDidLoad()
loadAddressURL() }
Could anyone point me into the correct direction on how to achieve the above mentioned result?
Many thanks in advance.

Answer 1

You can do that using NSURLProtocol, here's a quick example:
Subclass NSURLProtocol
class Interceptor: NSURLProtocol {
override class func canonicalRequestForRequest(request: NSURLRequest) -> NSURLRequest {
return request
}
override class func canInitWithRequest(request: NSURLRequest) -> Bool {
// returns true for the requests we want to intercept (*.png)
return request.URL.pathExtension == "png"
}
override func startLoading() {
// a request for a png file starts loading
// custom response
let response = NSURLResponse(URL: request.URL, MIMEType: "image/png", expectedContentLength: -1, textEncodingName: nil)
if let client = self.client {
client.URLProtocol(self, didReceiveResponse: response, cacheStoragePolicy: .NotAllowed)
// reply with data from a local file
client.URLProtocol(self, didLoadData: NSData(contentsOfFile: "local file path")!)
client.URLProtocolDidFinishLoading(self)
}
}
override func stopLoading() {
}
}
Somewhere in your code, register the Interceptor class:
NSURLProtocol.registerClass(Interceptor)
There's also a nice article on NSHipster if you want to read more about NSURLProtocol.