I hinted in my previous post that similar techniques could be used to bridge JavaScript to Objective-C on iOS, but that it would require using undocumented methods. As with the Mac-based solution, it’s not such a big deal so long as you’re only going to use it for private, debugging builds of your app. So how can it be done?

WebKit on iOS is for the most part famously, frustratingly hidden from developer use. As apps like Safari show, there is an extensive, powerful WebKit framework just as there is on the Mac, but iOS developers are limited to the comparatively impotent UIWebView.

But here’s a hint: UIWebView is itself a client of “proper WebKit,” and thus implements many of the powerful delegate methods that you would implement as the Mac delegate of a WebView. So if I were an iOS developer and wanted to play around with bridging WebView to Objective-C, I would simply subclass UIWebView, and override the delegate methods methods I am interested in:

#if DEBUG
@interface UIWebView (PrivateMethods)
- (void)webView:(UIWebView*)webView
      didClearWindowObject:(id)windowObject
      forFrame:(id)frame;
@end

@interface MyWebView : UIWebView
@end

@implementation MyWebView

// Override methods on UIWebView that it itself employs
// as delegate of a "proper" WebKit WebView object
- (void)webView:(UIWebView*)webView
      didClearWindowObject:(id)windowObject
      forFrame:(id)frame
{
   [super webView:webView didClearWindowObject:windowObject forFrame:frame];

   id myDelegate = [[UIApplication sharedApplication] delegate];
   [windowObject setValue:myDelegate forKey:@"appDelegate"];
}

@end

#endif

Set your WebView to use the custom class “MyWebView”, and now your iOS-based WebView can pass whatever information it needs to directly to your delegate, just as I illustrated for the Mac version.