UITextView Links with User Options

This application demonstrates how to detect links within a UITextView which open in a custom UIWebView controller. With the custom controller providing the user the option to open the url in mobile Safari.

Disclaimer

Please understand that using this technique probably won't get your app approved for the App Store from the review team. Please resort to other methods or check out my latest workaround here.

Detecting Links

There is surprisingly little to no information on the Internet regarding this solution. Detecting links within a UITextView is the easy part.

textView = [[UITextView alloc] init];
textView.text = @"Visit http://www.google.com for great good.";

textView.dataDetectorTypes = UIDataDetectorTypeLink;
textView.editable = NO;

URLs are detected by setting the dataDectorTypes parameter to UIDataDetectorTypeLink, optionally set it to UIDataDetectorTypeAll to detect all data types. This will highlight the URL allowing the user to touch the link, which will open in Safari. The caveat is having to set editable = NO.

Creating the Custom UIWebView Controller

I owe a lot of my UIWebView code to the open sourced version of TwitterFon. I added a UIToolbar to the bottom to hold a back button, forward button, refresh button, and the action button. I made it as Tweetie-like as I could for granularity. When you invoke the action button a UIActionSheet will pop up asking the user if they want to open the page in Safari.

But how do we open our links in our custom UIWebView controller in the first place?

This part was hard to figure out, initially. I eventually found this post on stackoverflow. What they say to do is basically create a UIApplication category to override openURL. You would also need some sort of watcher to keep track of your current view controller. I threw something hacky together and found that it worked.

@implementation UIApplication (Private)

- (BOOL)customOpenURL:(NSURL*)url
{
  AppDelegate *watcher = [[UIApplication sharedApplication] delegate];
  if (watcher.currentViewController) {
    [watcher.currentViewController handleURL:url];
    return YES;
	}
  return NO;
}

@end

This solution works, but it's win/lose. You have the ability to open all links in your custom webview, but now it's impossible to invoke UIApplication's openURL which opens Safari since you are overriding the method.

One fix is actually to subclass UIApplication. Then, inside your category you can invoke [super openURL:url] if your watcher is nil, for instance. But subclassing UIApplication can be somewhat funky.

The solution I ended up with was much cooler anyway.

Method Swizzling

I had never heard of method swizzling before, but it sounded insane so I figured why not try it out. There's plenty of resources on the Internet to hold your hand through this part. Basically, method swizzling is just a way to swap method implementations.

It's very hacky and somewhat dangerous, so I don't necessarily recommend it, but it works and does a swell job at it. Here's what swizzling looks like in a nutshell.

#import <objc/runtime.h>
..

Method customOpenUrl = class_getInstanceMethod([UIApplication class], @selector(customOpenURL:));
Method openUrl = class_getInstanceMethod([UIApplication class], @selector(openURL:));
method_exchangeImplementations(customOpenUrl, openUrl);

With method swizzling, you swap implementations between separate methods. For this to be possible with OpenURL I still had to create a UIApplication (Private) category, but I named my new method customOpenURL:(NSURL*)url instead. Now I could swizzle between OpenURL and customOpenURL. All I had to do now was swizzle the implementations on initialization and when the user is in the custom UIWebView controller I unswizzle them to open in Safari. Great success.

I understand this might be confusing, especially if you're new to Objective-C or iPhone development, but this is a really handy trick. I'm sure there's plenty of things out there that you can apply this solution to. But my main focus was getting URL detection to open in a custom UIWebView or Safari, and I found that solution. I hope this helps!

The Blog Post

Can be found here