On Github I’ve got a NSUrlCache implementation that adds simple offline caching. Dropping this in to an iOS application will allow UIWebViews to work offline.
It doesn’t include precaching (although that could be done by bundling cached files with the app) or any smarts around cache invalidation or caching while online. In fact if the device is online it will always use the online resource and update the cached item. The only thing it adds is offline capability.
The cache is assigned to the static NSUrlCache.SharedCache so add this to your AppDelegate.FinishedLaunching or similar:
var cachePath = Path.Combine(Environment.GetFolderPath (Environment.SpecialFolder.MyDocuments), "urlcache");
NSUrlCache.SharedCache = new OfflineUrlCache(cachePath);
This will only affect anything that uses NSUrls like the UIWebView. So anything that is in .NET world like RestSharp won’t be affected. Which is usually what you would want.