Question

I’m currently developing a small, JavaScript based drawing application on iPad. I’ve simply wrapped it inside UIWebView like this. Now the thing is that I can’t figure out how to save an image from the app so that it’s stored on iPad photos.

Is there some simple way to bridge JavaScript code with Objective-C one? I guess I could pass a string containing PNG image data from the JS side and then use Objective-C to save it to the photo gallery somehow.

Answer 1

Yes, there is a way to bridge javascript from a UIWebView to Obj-C code.

Set your UIWebView delegate, and in your delegate paste in the following method

//
// Map links starting with file://
//            ending with #action
// with the action of the controller if it exists.
//
// Open other links in Safari.
- (BOOL)webView: (UIWebView*)webView shouldStartLoadWithRequest: (NSURLRequest*)request navigationType: (UIWebViewNavigationType)navigationType {
    NSString *fragment, *scheme;

    if (navigationType == UIWebViewNavigationTypeLinkClicked) {
        [webView stopLoading];
        fragment = [[request URL] fragment];
        scheme = [[request URL] scheme];

        if ([scheme isEqualToString: @"file"] && [self respondsToSelector: NSSelectorFromString(fragment)]) {
            [self performSelector: NSSelectorFromString(fragment)];
            return NO;
        }

        [[UIApplication sharedApplication] openURL: [request URL]];
    }

    return YES;
}

Then you can write Obj-C methods that’ll handle the request. For example. In your webview you might have a button that has a link tag like

<a href="file://myGreatApp.com/saveImage">Click Me to Save Image </a>

The scheme is “file” the fragment is “saveImage”. You can now write an Obj-C method

-(void)saveImage;

That will be called every time a user clicks on the link.

Edit:
If you want to pass string parameters in your method, simply append them to your fragment url using javascript. So instead you might have

<a href="file://myGreatApp.com/saveImage*asdgo8asdgl35lkjasgd807ll12">Click Me to Save Image </a>

Then in your Obj-C code, split the fragment on the char ‘*’. Use the first half as your selector and the second half as the parameter.