Xamarin.Forms - Getting Started With Prism

Introduction

Xamarin.Forms code runs on multiple platforms - each of which has its own filesystem. This means that reading and writing files are most easily done using the native file APIs on each platform. Alternatively, embedded resources are a simpler solution to distribute data files with an app.

MVVM

MVVM - Model View ViewModel

MVVM Is the design pattern to separate the user interface & business logic concerns. I suppose that you heard something about it. This pattern created by Microsoft is widely used with applications created with .NET Framework but not only because you can also use it with Xamarin.

Prism

Prism is a framework for building loosely coupled, maintainable, and testable XAML applications in WPF, Windows 10 UWP, and Xamarin Forms. Prism provides an implementation of a collection of design patterns that are helpful in writing well-structured and maintainable XAML applications, including MVVM, dependency injection, commands, EventAggregator, and others.

Prism Containers

Unity
DryIoc

Unity is the container I use and recommend the most. Unity is the most popular container due to it being the container that Brian has used for years and it is the first (and for a long time only) container available in the Templates. Unity is also about average with regards to its benchmark performance.

DryIoc is the container under active development, it's very fast, and works well with the current release of Prism. Also important is that when I have had questions or issues the maintainer has been very quick to address the issue or answer the question I had. It's for all of these reasons I continue to recommend the container.

Go with Prism Unity Container

Prerequisites

Visual Studio 2017 or later (Windows or Mac)

Setting up a Xamarin.Forms Project

Start by creating a new Xamarin.Forms project. You wíll learn more by going through the steps yourself.

Create a new or existing Xamarin forms (.Net standard) Project with Android and iOS Platform.

Install "Prism.Unity.Forms" Nuget

Now, add the following NuGet Packages.

Prism.Unity.Forms

Go to Solution Explorer and select your solution. Right-click and select "Manage NuGet Packages for Solution". Search "Prism.Unity.Forms" and add Package. Remember to install it for each project (.NET Standard, Android, iO, and UWP).

Change Application to PrismApplication

After installing Prism.Unity.Prism, Change Application to PrismApplication in App.Xaml

App.xaml

<?xml version="1.0" encoding="utf-8"?>
<prism:PrismApplication xmlns="http://xamarin.com/schemas/2014/forms"
xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
xmlns:prism="clr-namespace:Prism.Unity;assembly=Prism.Unity.Forms"
x:Class="XMonkey.App">
<Application.Resources>
</Application.Resources>
</prism:PrismApplication>

Register NavigationService

Change application to PrismApplication and add IPlatformInitializer to App Constructor.

Then register your content page and ViewModel using IContainerRegistry

override OnInitialized (Initialize Components)
override RegisterTypes (Navigation Service Register)

Refer to the following code snippet,

using Prism;
using Prism.Ioc;
using Prism.Unity;
public partial class App : PrismApplication
{
//public App()
//{
// InitializeComponent();
// //DependencyService.Register<MockDataStore>();
// Routing.RegisterRoute("aboutPage", typeof(AboutPage));
// Routing.RegisterRoute("itemsPage", typeof(ItemsPage));
// MainPage = new AppShell();
//}
#region Prism
public App(IPlatformInitializer platformInitializer = null) : base(platformInitializer) { }
protected override void OnInitialized()
{
InitializeComponent();
NavigationService.NavigateAsync(PageConstants.MY_PAGE);
}
protected override void RegisterTypes(IContainerRegistry containerRegistry)
{
containerRegistry.RegisterForNavigation<AboutPage, AboutPageViewModel>();
containerRegistry.RegisterForNavigation<MyPage, MyPageViewModel>();
}
#endregion
}

Platform Setup

Android

Need to change IPlatformInitializer in LoadApplication.

MainActivity.cs

using Prism;
using Prism.Ioc;
namespace XMonkey.Droid
{
[Activity(Label = "XMonkey", Icon = "@mipmap/icon", Theme = "@style/MainTheme", MainLauncher = true, ConfigurationChanges = ConfigChanges.ScreenSize | ConfigChanges.Orientation)]
public class MainActivity : global::Xamarin.Forms.Platform.Android.FormsAppCompatActivity
{
protected override void OnCreate(Bundle savedInstanceState)
{
TabLayoutResource = Resource.Layout.Tabbar;
ToolbarResource = Resource.Layout.Toolbar;
base.OnCreate(savedInstanceState);
global::Xamarin.Forms.Forms.SetFlags("Shell_Experimental", "Visual_Experimental", "CollectionView_Experimental", "FastRenderers_Experimental");
Xamarin.Essentials.Platform.Init(this, savedInstanceState);
global::Xamarin.Forms.Forms.Init(this, savedInstanceState);
//Change LoadApplication IPlatformInitializer
LoadApplication(new App(new AndroidInitializer()));
}
public class AndroidInitializer : IPlatformInitializer
{
public void RegisterTypes(IContainerRegistry containerRegistry)
{
}
}
public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Android.Content.PM.Permission[] grantResults)
{
Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);
base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
}
}
}

iOS

Need to change IPlatformInitializer in LoadApplication.

AppDelegate.cs

using Prism;
using Prism.Ioc;
using UIKit;
namespace XMonkey.iOS
{
[Register("AppDelegate")]
public partial class AppDelegate : global::Xamarin.Forms.Platform.iOS.FormsApplicationDelegate
{
public override bool FinishedLaunching(UIApplication app, NSDictionary options)
{
Xamarin.Calabash.Start();
global::Xamarin.Forms.Forms.Init();
//Change LoadApplication IPlatformInitializer
LoadApplication(new App(new iOSInitializer()));
return base.FinishedLaunching(app, options);
}
}
public class iOSInitializer : IPlatformInitializer
{
public void RegisterTypes(IContainerRegistry containerRegistry)
{
}
}
}

MVVM BindingContext

You don't need to set BindingContext to your ViewModel to ContentPage. Just create a ContentPage name ending with Page. (Ex: MyPage). Create a ViewModel name staring with ContentPage Name (ex: MyPageViewModel).

ViewModelLocator

If Viewmodel BindingContext is not working, follow the below steps.

ContentPage.cs

ViewModelLocator.SetAutowireViewModel(this,true);

ContentPage.Xaml

xmlns:prism="clr-namespace:Prism.Mvvm;assembly=Prism.Forms"
prism:ViewModelLocator.AutowireViewModel="True"

Click the "Play" button to try it out.

Wow, it's working. Xamarin.Forms - Getting Started With Prism

I hope you have understood how to how to use Prism in existing Xamarin.Forms app.

Thanks for reading. Please share your comments and feedback. Happy Coding Xamarin.Forms - Getting Started With Prism