When did caching in a UIWebView start working?

Question

I've been testing an iPhone view controller that uses a UIWebView to load external content, as opposed to resources in the project's bundle. Another engineer noticed that the web view wasn't caching at all, so I went into do some research. Some older questions indicated that UIWebView's just couldn't cache external content.

Previous SO Questions on UIWebView caching:

• Is it possible to cache resources loaded in an iPhone UIWebView?
• Is it possible to cache web pages with a UIWebView?
• Reading HTML content from a UIWebView

Those posts were pretty deflating, but I noticed that they were all asked before iOS 4.0 came out. I tested the following approach for caching, which seemed pretty straight-forward.

NSURLRequest *request = [NSURLRequest requestWithURL:myUrl 
      cachePolicy:NSURLRequestReturnCacheDataElseLoad timeoutInterval:30];
[webView loadRequest:request];

This seems to work great on iOS 4.3 but doesn't work at all on iOS 3.0. I tested this by pointing the devices to a Charles proxy (on iPhone, Settings -> WiFi, Manual proxy) and recording the traffic to my server.

Did the UIWebView start observing the cache policy in iOS 4.0? Can anyone else confirm this or am I just imagining things?

Answer 1

Yes, in iOS 4.0 the cache started working.

There is a class in Foundation framework that's in charge of handling this, it's NSCache. It's been in Mac OS X from ages but it wasn't implemented in iOS until iOS 4.0. Even then it was implemented only partially: it didn't support disk caching but only memory caching (so the cache was very unreliable due to memory being released when requested by the system).

NSCache received an update in iOS 5.0 that added support for disk caching and it now works like the Mac version and can be used with no problem.