Programming iOS 6, 3rd Edition

Communicating with a Web View

Having loaded a web view with content, you don’t so much configure or command the web view as communicate with it. There are two modes of communication with a web view and its content:

Load requests

When a web view is asked to load content, possibly because the user has tapped a link within it, its delegate is sent the message webView:shouldStartLoadWithRequest:navigationType:. This is your opportunity to interfere with the web view’s loading behavior; if you return NO, the content won’t load.

The second argument is an NSURLRequest, whose URL property you can analyze (very easily, because it’s an NSURL). The third argument is a constant describing the type of navigation involved, whose value will be one of the following:

• UIWebViewNavigationTypeLinkClicked
• UIWebViewNavigationTypeFormSubmitted
• UIWebViewNavigationTypeBackForward
• UIWebViewNavigationTypeReload
• UIWebViewNavigationTypeFormResubmitted
• UIWebViewNavigationTypeOther (includes loading the web view with content initially)

JavaScript execution

You can speak JavaScript to a web view’s content by sending it the stringByEvaluatingJavaScriptFromString: message. Thus you can enquire as to the nature and details of that content, and you can alter the content dynamically.

The TidBITS News app uses webView:shouldStartLoadWithRequest:navigationType: to distinguish between the user tapping an ordinary link and tapping the Listen button (shown in Figure 24-2). The onclick script for the <a> tag surrounding ...