JSからカスタムURIスキームでObjective-Cの処理を呼ぶ。

MainViewController.m

// http://qiita.com/GeneralD/items/5a05f176ac2321e7a51b
#define CASE(str) if ([__s__ isEqualToString:(str)])
#define SWITCH(s) for (NSString *__s__ = (s); __s__; __s__ = nil)
#define DEFAULT

- (BOOL) webView:(UIWebView*)theWebView shouldStartLoadWithRequest:(NSURLRequest*)request navigationType:(UIWebViewNavigationType)navigationType
{
    NSURL *url = request.URL;

    if ([self isExternalUrl:url]) {
        [[UIApplication sharedApplication] openURL:url];
        return NO;
    }
    
    NetworkStatus status = [_reachablity currentReachabilityStatus];
    if (status == NotReachable) { // ReachableViaWWAN: 3G, ReachableViaWiFi: WiFi
        if (_openingOfflineScreen) {
            return YES;
        } else {
            _openingOfflineScreen = YES;
            [self loadOfflineScreen];
            return NO;
        }
    }
    
    if ([self isCustomUrl:url]) {
        [self processCustomUrl:url];
        return NO;
    }

    return [super webView:theWebView shouldStartLoadWithRequest:request navigationType:navigationType];
}

- (BOOL)isCustomUrl:(NSURL *)url
{
    return NSNotFound != [url.scheme rangeOfString:@"postmore"].location;
}

// ...

- (void)processCustomUrl:(NSURL*)url
{
    NSAssert(url, @"url is required");
    
    NSLog(@"custom url: %@", url);
    
    SWITCH(url.scheme) {
        CASE(@"postmore") { // redirect to the corresponding path on the web
            NSDictionary *postmore = [[NSBundle mainBundle] objectForInfoDictionaryKey:@"Postmore"];
            NSString *host = [postmore objectForKey:@"Host"];
            
            NSURLComponents *components = [NSURLComponents componentsWithURL:url resolvingAgainstBaseURL:NO];
            components.scheme = @"https";
            components.host = host;
            NSURL *requestUrl = components.URL;
            NSLog(@"redirect to: %@", [requestUrl absoluteString]);
            NSURLRequest *request = [NSURLRequest requestWithURL:requestUrl];
            [self.webView loadRequest:request];
            
            break;
        }
        CASE(@"postmore-instagram") { // share on instagram
            [self openInInstagram:url];
            
            break;
        }
        CASE(@"postmore-sharing") { // send to other applications
            [self openInOtherApps:url];
            
            break;
        }
        CASE(@"postmore-save") { // save to local camera roll
            [self saveToCameraRoll:url];
            
            break;
        }
        CASE(@"postmore-page-loaded") {
            [self prefetchSharableResources];
            [self informEndpointArn];
            
            break;
        }
        CASE(@"postmore-log") {
            [self logToXcode:url];
            
            break;
        }
        DEFAULT {
            NSLog(@"unsupported scheme: %@", url.scheme);
            
            break;
        }
    }
}

// ...