Prism and Xamarin Forms

Here’s the steps for getting Prism and Xamarin Forms up and running together. For this I’m using Visual Studio 2015. Refer to a previous post on how to get a Xamarin Forms application up and running in Visual Studio 2015 if you need to.

Note: I’m using the Unity container hence I’ll be demonstrating the code using Prism.Unity.Forms, there is support for alternate IoC containers such as NInject, Mef and Autofac. Prism.Unity.Forms will automatically include Prism.Core and Prism.Forms.

  • Create a Cross-Platform, Blank App (Xamarin.Forms Portable)
  • Using NuGet, install Prism.Unity.Forms (at the time of writing – you’ll need to click on the Include prerelease option), I’ve installed v6.2.0-pe5
  • For each of the projects you’ve created you’ll now need to go to each References section and add the Prism.Unity.Forms package from NuGet
  • Prism has a convention based approach to loading view model’s, so let’s create the two folders, Views and ViewModels off of the Portable project – in fact it’s the namespace that matters, so the expectation is for views to be in the Views namespace and likewise the view models should be in the ViewModels namespace.
  • Now add a MainPage.xaml file to the Views folder, so in the Portable project right mouse click, select Add | New Item and then from Cross-Platform select Forms Xaml Page, I’ve named mine MainPage
  • In the MainPage.xaml file you’ll see the Label is bound to a MainText property, so let’s now create a MainPageViewModel.cs file in the ViewModels folder to act as our view model for this page (the default convention is for the view model for a view to be named after the view with the suffix ViewModel, i.e. MyView by default maps to MyViewModel).
  • To allow Prism to auto wire up view models we need to add the following to the XAML file (to the ContentPage) 
    xmlns:mvvm="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
mvvm:ViewModelLocator.AutowireViewModel="True"
  • Derive the view model from BindableBase and implement the following code to simply get things up and running 
    public class MainPageViewModel : BindableBase
{
   public string MainText { get; } = "Hello Prism World";
}

    You’ll need to add using Prism.Mvvm; to resolve the BindableBase object.

  • Remove all the code from the App constructor as the MainPage will be supplied by Prism going forward.
  • Derive your App from PrismApplication instead of Application and implement the abstract methods as below 
    public class App : PrismApplication
{
   // add these methods
   protected override void OnInitialized()
   {
      NavigationService.NavigateAsync("MainPage");
   }

   protected override void RegisterTypes()
   {
      Container.RegisterTypeForNavigation<MainPage>();
   }
}

    You’ll need to add using Prism.Unity; to resolve PrismApplication.

    OnInitialized will automatically navigate to the “MainPage” view, the magic string maps to the type name MainPage as I’m sure you can see. But in the RegisterTypeForNavigation we can change this string mapping if preferred.