localStorage not persisting in OSX app (Xcode 4.3)

Question

From what I have seen, if you are building a OSX desktop HTML5 app and want localStorage to persist in your WebView wrapper, you need to do something like this:

Answer 1

OK, I have a solution. I looked at the source code to macgap and noticed how they were dealing with this issue.

It turns out the error message I was getting does make a little sense - I needed to declare an interface for WebPreferences first.

@interface WebPreferences (WebPreferencesPrivate)
- (void)_setLocalStorageDatabasePath:(NSString *)path;
- (void) setLocalStorageEnabled: (BOOL) localStorageEnabled;
@end

...

WebPreferences* prefs = [WebPreferences standardPreferences];
[prefs _setLocalStorageDatabasePath:"~/Library/Application Support/MyApp"];
[prefs setLocalStorageEnabled:YES];
[webView setPreferences:prefs];

Like I said, I'm new to Objective-C. I don't really get why the interface is needed in order to call those two methods (i.e. when I can call the other methods without the interface).

Answer 2

There's good news and there's bad news; I'm going to make the assumption that you want the bad news first (it'd be easier if I answered your question with the bad news first anyway).

The Bad News

The only answer to why this is happening is that Xcode 4.3 doesn't offer those methods anymore. That question that you linked to, "How do I enable Local Storage in my WebKit-based application?" was last active over a year ago (with the accepted answer being edited in early 2011). There have been at least two updates to Xcode since then (probably more and I'm just not remembering them), and it seems feasible to me that Apple would want to keep their private methods private, so it's safe to assume that they removed them as well as the support for setLocalStorageEnabled:.

The reasons that I don't think that there is any other answer to your problem are the following:

1. Both methods that you call on the WebPreferences instance are not supported. It's not just the private method, so Apple must have modified the WebPreferences class, removing not only setLocalStorageEnabled: but also support for private methods such as _setLocalStorageDatabasePath:. Why they supported private methods to begin with, I don't know, but they've definitely cracked down on their support because I haven't seen an opportunity to implement a private method in quite some time.
2. If implementing the private method (or even the other, public method) were possible, it'd be as easy as your code makes it out to be. If one looks at the linked question, they don't mention any difficult steps to getting the code to be supported. There isn't any way to import a private part of a framework such as WebKit without doing some heavy-lifting with regards to not only finding the private part but getting it into your code as well. Even if you can get those methods supported in your code after all of that heavy-lifting, it'd be highly unlikely that Apple would be very happy with it and they'd probably deny your app from the app store.

Sorry to be a Debbie-downer about it all, but I just don't think that your code would work anymore without some deep diggging and large workarounds. If you want it to work easily, you'll probably have to go back to early 2011 and make your app then instead.

The Good News

There is probably some solution that doesn't involve private and unsupported methods that I'm just not aware of because of my lack of experience using WebKit. Instead of looking for an answer for why your code isn't working, I'd start looking for alternatives for what your code is supposed to do.

Answer 3

I have found a solution to the persistence problem. see my post at

Local Storage in webview is not persistent