MonoTouch: creating multiplatform apps using Portable Class Libraries

Question

My scenario: trying to port a small part of an application created by our company from native code (ObjC for iOS / Java for Android) to C-Sharp. The project will interact with our webservices. Goal of this project is figuring out how feasible it is to port our whole app to Mono.

To create URLs, I'd like to use String.Format(). I thought it'd be a wise idea to put this 'service layer' inside a Portable Class Library (PCL) since I don't expect this code to change across platforms. Sadly, it seems the String library is not available for PCLs.

So my question is the following:

1. I think the main advantage of PCLs over "normal" libraries is that they shouldn't need a recompile for different platforms. Is this assumption correct?
2. This experience makes me think that for the moment PCLs are rather limited. Should I try to stick with PCLs and work around these kinds of issues, or might it be better to stick with a "normal" library for now? --- I'll assume the "normal" library has more functionality exposed.

Answer 1

You can use PCLs currently across many platforms, but it does require some small hacks to your setup.

These hacks are listed in http://slodge.blogspot.co.uk/2012/12/cross-platform-winrt-monodroid.html

Once you've got those working then the functionality available is quite broad - and it definitely includes things like String.Format

For the situations where the PCL profile is not broad enough, then you can use several techniques for extending them - see http://blogs.msdn.com/b/dsplaisted/archive/2012/08/27/how-to-make-portable-class-libraries-work-for-you.aspx . The technique I generally use is to use MvvmCross Plugins - which are basically PCL interfaces with platform specific implementations. But these plugins are generally at the level of 'make bluetooth work' rather than at the level of String.Format

I do lots of PCL work across WinRT, WP, WPF, MonoTouch and Mono for Android - see http://slodge.blogspot.co.uk/p/mvvmcross-quicklist.html for lots of links to PCL work.

It's true that Xamarin have recommended not using PCLs for a couple of years, but that situation has now changed and the official support for PCLs is under way - see http://slodge.blogspot.co.uk/2013/02/the-future-is-portable.html

From a development perspective - especially from the point of view of using refactoring and testing tools - I don't hesitate to recommend you use PCLs now... especially for operations at the String.Format level. However, each project is unique... so it's not always the right answer.

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One important note: right now it's better to not reuse the PCL binary files across to the MonoTouch platform - for now, build your portable libraries against the specific MonoTouch library platform. See http://slodge.blogspot.co.uk/2013/01/almost-portable-binaries.html?m=1

Answer 2

Perhaps you want to look at the efforts other who have got PCLs working to a considerable degree with monotouch and monodroid.

For example see http://www.slideshare.net/cirrious/mvvm-cross-going-portable . You'll also find instructions on how to setup PCL support for MVVMCross here http://slodge.blogspot.co.uk/2012/09/mvvmcross-vnext-portable-class.html .

Xamarin has recently committed to providing far greater PCL support rather than some of the workarounds that people have been having to make, but it is worth the effort.