Is there a way to define some kind of handling mechanism in Android and iOS that would allow me to do intercept either of the following:
myapp:///events/3/
- or -
http://myapp.com/events/3/
I'd like to 'listen' for either the protocol or the host, and open a corresponding Activity / ViewController.
I'd like too if these could be as system wide as possible. I imagine this will be more of an issue on iOS, but I'd ideally be able to click either of those two schemes, as hyperlinks, from any app. Gmail, Safari, etc.
Update: This is a very old question, and things have changed a lot on both iOS and Android. I'll leave the original answer below, but anyone working on a new project or updating an old one should instead consider using deep links, which are supported on both platforms.
On iOS, deep links are called universal links. You'll need to create a JSON file on your web site that associates your app with URLs that point to parts of your web site. Next, update your app to accept a NSUserActivity object and set up the app to display the content that corresponds to the given URL. You also need to add an entitlement to the app listing the URLs that the app can handle. In use, the operating system takes care of downloading the association file from your site and starting your app when someone tries to open one of the URLs your app handles.
Setting up app links on Android works similarly. First, you'll set up an association between your web site(s) and your app, and then you'll add intent filters that let your app intercept attempts to open the URLs that your app can handle.
Although the details are obviously different, the approach is pretty much the same on both platforms. It gives you the ability to insert your app into the display of your web site's content no matter what app tries to access that content.
Original answer:
For iOS, yes, you can do two things:
Have your app advertise that it can handle URL's with a given scheme.
Install a protocol handler to handle whatever scheme you like.
The first option is pretty straightforward, and described in Implementing Custom URL Schemes. To let the system know that your app can handle a given scheme:
update your app's Info.plist with a CFBundleURLTypes entry
implement -application:didFinishLaunchingWithOptions: in your app delegate.
The second possibility is to write your own protocol handler. This works only within your app, but you can use it in conjunction with the technique described above. Use the method above to get the system to launch your app for a given URL, and then use a custom URL protocol handler within your app to leverage the power of iOS's URL loading system:
Create a your own subclass of NSURLProtocol.
Override +canInitWithRequest: -- usually you'll just look at the URL scheme and accept it if it matches the scheme you want to handle, but you can look at other aspects of the request as well.
Register your subclass: [MyURLProtocol registerClass];
Override -startLoading and -stopLoading to start and stop loading the request, respectively.
Read the NSURLProtocol docs linked above for more information. The level of difficulty here depends largely on what you're trying to implement. It's common for iOS apps to implement a custom URL handler so that other apps can make simple requests. Implementing your own HTTP or FTP handler is a bit more involved.
For what it's worth, this is exactly how PhoneGap works on iOS. PhoneGap includes an NSURLProtocol subclass called PGURLProtocol that looks at the scheme of any URL the app tries to load and takes over if it's one of the schemes that it recognizes. PhoneGap's open-source cousin is Cordova -- you may find it helpful to take a look.