We recently shipped the Unified API for Xamarin.iOS. The Unified API is a huge step forward for Xamarin.iOS, allowing a single source code to produce both 32 and 64-bit iOS Applications, a more streamlined and consistent API, and a much better story for sharing code with Xamarin.Mac applications.
64-bit iOS apps, which until recently could only be run on the most recent devices (iPhone 5s, iPad Air, and iPad Mini Retina), can now also run on the iPhone 6 and iPhone 6 Plus. This is fantastic news, but before you convert your apps to the Unified API, there are a couple of important things to consider, as the Xamarin toolchain matures to match the API.
As of today, the most compelling reason to switch to the Unified API is if you want to create app extensions, which requires developers to produce both 32 and 64-bit binaries to Apple. You can create a new application project using the Unified API or you can follow these instructions to update an existing Xamarin.iOS app.
There are currently some limitations on apps using the Unified API which I’ve outlined below:
Unfortunately, existing Xamarin.iOS components need to be re-built against the Unified API, so while we (and the community) are working to update the component code, you will not be able to include these in your app. A workaround for open-source projects is to download and compile the code yourself as part of your Unified API project.
NuGet will support Unified packages starting with version 2.8.3, a new build is now available at CodePlex.
Custom Control Designer Support
Our designer currently does not have the ability to render your custom controls in the editing surface when you use the Unified API. We are working on this.
Xamarin is prioritizing updating our components so that you can start using them in your Unified API iOS apps, as well as updating the iOS Designer custom control renderer.
Our recommendation therefore is this: if you don’t need to utilize the App Extensions framework today, hold off on moving to our preview Unified API until the toolchain and components have caught up.