Best practice: How to call Objective-C code from JavaScript

Question

I've been looking for a way to call Objective-C code from some JavaScript in my UIWebView. A lot of topics has been created about this, and some of them are recommending the procedure done in the blog post UIWebView Secrets - Part3 - How to Properly Call ObjectiveC From Javascript, where UIWebViewDelegate methods are hacked to call native Objective-C code from. Is this still the best way to do this? It seems that PhoneGap has a way to do this, but I cannot find out how to. But if their procedure is equal to this, I cannot see why I should include their library just to do this.

Which procedure is currently best practice to do this?

Sree · Accepted Answer · 2012-03-09 12:15:04Z

Without any external framework we can do that.To achieve this like phone we have to use webView. For example, If you need to call an objective c function when a button is clicked in the webview.When the onclick of your button in the html page calls a javascript, just add an iFrame which will include the function name of the objective C function.

eg:

var iframe = document.createElement("IFRAME");
    iframe.setAttribute("src", "js-frame:" + functionName + ":" + callbackId);
    document.documentElement.appendChild(iframe);
    iframe.parentNode.removeChild(iframe);
    iframe = null

;

This iFrame can be accesed in your webView Delegate implemented in your ParentView of the webView, like-

- (BOOL)webView:(UIWebView *)webView2 
shouldStartLoadWithRequest:(NSURLRequest *)request 
 navigationType:(UIWebViewNavigationType)navigationType {

    NSString *requestString = [[request URL] absoluteString];




    if ([requestString hasPrefix:@"js-frame:"]) {

        NSArray *components = [requestString componentsSeparatedByString:@":"];

        NSString *function = (NSString*)[components objectAtIndex:1];
        int callbackId = [((NSString*)[components objectAtIndex:2]) intValue];

                                  stringByReplacingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
        ;

        [self handleCall:function callbackId:callbackId];

        return NO;
    }

    return YES;
}

The handleCall will have to handle the invoking of your intended method having name "function"

score 0 · Accepted Answer · 2012-03-09 13:50:40Z

0

There is no (public) API to do this other than using a custom URL scheme inside your JS code to invoke javascript.

Let's say you load the URL myproto://invokeMethodA in your JS code like so

window.location.href = "myproto://invokeMethodA";

you can intercept that load in UIWebViews delegate method

– webView:shouldStartLoadWithRequest:navigationType:

and do your stuff. Make sure you return NO to not actually perform the the request.

edited Mar 9, 2012 at 13:50

answered Mar 9, 2012 at 12:15

user187676

Comments

dhrm · Accepted Answer · 2012-03-21 12:32:36Z

0

I end up using the NativeBridge plugin recommended in the blog post.

answered Mar 21, 2012 at 12:32

dhrm

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2 Comments

Volomike Over a year ago

Does windowScriptObject not work with iOS like it does with OSX? I'm using that at least with NSWebView on OSX, rather than UIWebView.

Volomike Over a year ago

Also, for readers of this answer, and sort of slightly related, I noticed that IFRAMEs inside the NSWebView component can call the ObjC injected bridge in the DOM by calling window.parent.objc.classMethod() where objc might be what you wanted windowScriptingObject to call your object, and classMethod() is any class method you wanted to call.

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