Possible for UIWebView to detect when a Javascript dialog is about to be shown?

Question

I'm new to iOS development. I come from an Android background.

I'd like to know whether it's possible for a UIWebView to detect when a Javascript alert/confirm/prompt dialog is about to be shown? (Similar to how the shouldStartLoadWithRequest method of UIWebViewDelegate is called before a web view begins loading a frame.)

The Android equivalent of what I'm looking for is WebChromeClient's onJSAlert(...), onJsConfirm(...) and onJsPrompt(...) methods, and by means of these methods the application can decide whether to show a given dialog or to block it.

How and where do you invoke the alerts? And what do you intend to do that the UIWebView should know about the Alert? — joern, Apr 10 '14 at 14:30
[This article](http://blog.impathic.com/post/64171814244/true-javascript-uiwebview-integration-in-ios7) might be useful to you. — 67cherries, Apr 10 '14 at 14:38
I didnt understand what exactly you want to do but you cant detect it, but you can request and take an answer like stringOrWhateverIsYourReturnOnObjectiveC=[yourUIWebView stringByEvaluatingJavaScriptFromString:@"YourJavascriptFunction"]; — Yucel Bayram, Apr 10 '14 at 14:53

joern · Accepted Answer · 2014-04-10T15:03:41.110

UIWebView does not have a method that is called when a Javascript alert is about to be shown. However you can use shouldStartLoadWithRequest: to inform the UIWebView about the alert and then decide whether to display it or not:

In your Javascript when you want to invoke an alert do this:

window.location.href = "alert://MESSAGE_TEXT";

In your UIWebView's delegate you can intercept that request and decide if you want to invoke the alert via javascript:

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

   switch (navigationType) {
      case UIWebViewNavigationTypeOther:
         if ([[request.URL scheme] isEqualToString:@"alert"]) {
            NSString *message = [request.URL host];
            if (SHOULD_SHOW_ALERT) {
               // the alert should be shown
               [webView stringByEvaluatingJavaScriptFromString:@"showAlert()"];
            } else {
              // don't show the alert
              // just do nothing
            }

            return NO;
         }
         break;
      default:
        //ignore
   }
   return YES;
}

I don't know if you need to send the message text to the UIWebView but I included it so that you can see how you can send parameters to the UIWebView. You could add more parameters in the URL's path.

Obviously you have to exchange SHOULD_SHOW_ALERT with your own if clause that's determines whether to show the alert or not and you have to add the showAlert() function to your Javascript.

Possible for UIWebView to detect when a Javascript dialog is about to be shown?

1 Answers1