How to handle app URLs in a UIWebView?

I recently found that my UIWebView was choking on ITMS links. Specifically, from the UIWebView in my app, if I navigate to a site such as this one and click the "Available on the App Store" link, UIWebView would error out with "Error Domain=WebKitErrorDomain Code=101 The URL can't be shown."

After a bit of Googling, I realized that I needed to catch requests for app links and have iOS handle them. I started out by looking to see if the scheme starts with "itms" in -webView:shouldStartLoadWithRequest:navigationType:, but realized that there might be other kinds of app links that the system can handle. So I came up with this, instead:

- (void)webView:(UIWebView *)wv didFailLoadWithError:(NSError *)error {
    // Give iOS a chance to open it.
    NSURL *url = [NSURL URLWithString:[error.userInfo objectForKey:@"NSErrorFailingURLStringKey"]];
    if ([error.domain isEqual:@"WebKitErrorDomain"]
        && error.code == 101
        && [[UIApplication sharedApplication]canOpenURL:url])
    {
        [[UIApplication sharedApplication]openURL:url];
        return;
    }

    // Normal error handling…
}

I have two questions about this:

1. Is this sane? I'm specifically checking for the error domain and error code and fetching the URL string from the userInfo. Is that stuff likely to remain?
2. This does work for the above-linked app store link, but when I switch back to my app, there appears to have been a subsequent failed request that failed with "Frame load interrupted". how can I get rid of that? It doesn't happen when I have the OS handle the request from -webView:shouldStartLoadWithRequest:navigationType:, so it's a bit annoying.

How do you handle such requests?

Here's what I came up with. In webView:shouldStartLoadWithRequest:navigationType:, I ask the OS to handle any non-http and non-https requests that it can, like so:

- (BOOL)webView:(UIWebView *)wv shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {

    // Determine if we want the system to handle it.
    NSURL *url = request.URL;
    if (![url.scheme isEqual:@"http"] && ![url.scheme isEqual:@"https"]) {
        if ([[UIApplication sharedApplication]canOpenURL:url]) {
            [[UIApplication sharedApplication]openURL:url];
            return NO;
        }
    }
    return YES;
}

This works very well except for the bloody "Frame Load Interrupted" error. I had thought that by returning false from webView:shouldStartLoadWithRequest:navigationType: that the web view would not load the request and therefore there would be no errors to handle. But even though I return NO above, I still "Frame Load Interrupted" error. Why is that?

Anyway, I'm assuming it can be ignored in -webView:didFailLoadWithError::

- (void)webView:(UIWebView *)wv didFailLoadWithError:(NSError *)error {
    // Ignore NSURLErrorDomain error -999.
    if (error.code == NSURLErrorCancelled) return;

    // Ignore "Fame Load Interrupted" errors. Seen after app store links.
    if (error.code == 102 && [error.domain isEqual:@"WebKitErrorDomain"]) return;

    // Normal error handling…
}

And now iTunes URLs work properly, as do mailto:s and app links.

Starting with Theory's code, examine the URL for "itms" scheme(s) (this method can be called multiple times due to redirects). Once you see an "itms" scheme, stop the webView from loading and open the URL with Safari. My WebView happens to be in a NavigationController, so I pop out of that after opening Safari (less flashing).

- (BOOL)webView:(UIWebView*)webView shouldStartLoadWithRequest:(NSURLRequest*)request 
  navigationType:(UIWebViewNavigationType)navigationType 
{
    if ([[[request URL] scheme] isEqualToString:@"itms-apps"]) {
        [webView stopLoading];
        [[UIApplication sharedApplication] openURL:[request URL]];
        [self.navigationController popViewControllerAnimated:YES];
        return NO;
    } else {
        return YES;
    }
}

Does it help if you register your app for handling itms: links?

e.g. http://inchoo.net/iphone-development/launching-application-via-url-scheme/

You may start with scheme http but then get an itms redirect, which could fail if your app is not registered as handling that scheme.