Xamarin + JSON.Net

Question

I'm having trouble understanding why the Newtonsoft JSON parser has to be device specific under Xamarin. I cannot seem to find any way to have the parser exist in a common, shared library. I'm using the Tasky Pro sample app. I can get the JSON.Net DLLs from the Xamarin store to work in the Android and iOS projects, however that makes no architecural sense. E.g., the SQLite stuff is all in a shared lib, as you'd expect - as one set of c# source files.

Ideally I'd like to just add some kind of reference to "Tasky.Core" and be able to serialize/deserialize JSON.

Is there any way to get JSON.Net to work in a shared library (across droid/ios/wp8)? The source is pretty huge to try to manage as linked files, if that's even possible...

If not, is there some alternative way of managing JSON that will work in this way?

Answer 1

You should be able to use the JSon.NET NuGet Package for this. The implementation is actually platform-specific [1], but NuGet will transparently take care of that for you and pick the correct one for you.

Note that you need Mono 3.2.6 and Xamarin.iOS 7.0.6 for this, which just hit the alpha channel this week, I have just fixed some critical bugs in this area. You should also upgrade the NuGet Add-In in Xamarin Studio to the latest version (0.8), which contains several PCL-related bug fixes.

Simply add the NuGet Add-In to Xamarin Studio if you have not done so already, then search for "JSon.NET", the add-in will automatically install the package and add the required library references for you.

[1] The NuGet package contains different .dll's for different target frameworks and then picks and references the best one for your project - so your application will only contain a single implementation, but an iOS app may use a different one than a desktop application.

Update 01/14/14:

NuGet packages usually contain different implementations - unfortunately, not all of them will work with Xamarin.iOS due to APIs such as Reflection.Emit or Full DLR that are not available on iOS.

If you look into the packages/Newtonsoft.Json.5.0.8/lib/ directory, you'll see different sub-directories - each of these contain a different implementation and NuGet will use the one that best fits the current target framework. Unfortunately, NuGet does not always pick the right one :-(

For Newtonsoft.Json.5.0.8, the "portable-net45+wp80+win8" implementation uses DLR features that are not available on iOS, the "portable-net40+sl4+wp7+win8" one is ok. So if you add the NuGet package to a PCL that's targeting for instance Profile136, you'll get the correct implementation.

There is no GUI to choose another implementation, but you can edit the .csproj file. Replace

<Reference Include="Newtonsoft.Json">
  <HintPath>..\packages\Newtonsoft.Json.5.0.8\lib\portable-net45+wp80+win8\Newtonsoft.Json.dll</HintPath>
</Reference>

with

<Reference Include="Newtonsoft.Json">
  <HintPath>..\packages\Newtonsoft.Json.5.0.8\lib\portable-net40+sl4+wp7+win8\Newtonsoft.Json.dll</HintPath>
</Reference>

and it should work.

In general, when you're getting an error message about missing types after adding a new NuGet package, go to the corresponding package directory and grep -r for that symbol - chances are that there's a different implementation which does not use this type.

Hopefully, a more elegant solution will be available in the future, but that needs coordination with the NuGet team and package authors, so it'll take some time.