Onionizing Xamarin Part 3

For those who just want code: https://github.com/SuavePirate/Xamarin.Onion 

Don’t forget:

  1. Part 1 on the general project structure: Onionizing Xamarin Part 1
  2. Part 2 on our Domain and Application layers: Onionizing Xamarin Part 2

A strong and scale-able architecture is important in applications, especially in Mobile Apps. APIs and SDKs are constantly changing, new technology is constantly released, and team sizes are always changing. A solid Onion Architecture can save a development team a lot of time by making it simple to change service implementations, restrict access to certain areas, making logic flow easy to follow, and making testing isolated blocks of code easier.

Some of the important topics this will cover:

  • Separation of Concerns
  • Inversion of Control
  • Dependency Injection
  • Model-View-ViewModel
  • Testability
  • Why all these things are important

Part 3

In this section, we’ll start to dive into the code for our infrastructure layers (or at least what is important), including our business logic and data logic.

Let’s dive into the data layer.

Infrastructure.Data

This layer is our actual implementation of our Domain definitions, so we are going to implement things such as our Repositories, DataProviders, Stores, or anything else that interacts with our data directly.

From our previous post we defined our IGenericStore + IUserStore and our IGenericRepository + IUserRepository, so now let’s implement them.

GenericStore.cs and UserStore.cs

public class GenericStore<T> : IGenericStore<T>
{
    public List<T> Data { get; set; }
    public GenericStore()
    {
        Data = new List<T>();
    }
}

public class UserStore : GenericStore<User>, IUserStore
{
}

For the sake of just testing data, our store just contains a collection of data, however, this is where you could implement an observable collection, or more complex data types as well.

Now a look at the repositories – Our implementation of our repository is just going to use in-memory storage, but this is a place where you could implement SqlLite, Azure Mobile Tables, or local file storage instead. You could implement all of these easily and just switch out in your UserRepository which one it inherits! That’s one of the biggest bonuses of our Onion Architecture. The github repository demonstrates this well: https://github.com/SuavePirate/Xamarin.Onion/blob/master/src/OnionTemplate/OnionTemplate.Infrastructure.Data/Repositories/UserRepository.cs

GenericMemoryRepository.cs and UserRepository.cs

public class GenericMemoryRepository<T> : IGenericRepository<T>
{
    private readonly IStoreManager _storeManager;
    public GenericMemoryRepository(IStoreManager storeManager)
    {
        _storeManager = storeManager;
    }
    public void Add(T entity)
    {
        _storeManager.Set<T>().Data.Add(entity);
    }

    public void AddRange(IEnumerable<T> entities)
    {
        _storeManager.Set<T>().Data.AddRange(entities);
    }

    public Task CommitAsync()
    {
        return Task.FromResult(false); // we don't need to explicitly save changes
    }

    public Task<T> FindAsync(Func<T, bool> predicate)
    {
        var entity = _storeManager.Set<T>().Data.Where(predicate).FirstOrDefault();
    return Task.FromResult(entity);
    }

    public Task<IEnumerable<T>> GetAsync(Func<T, bool> predicate)
    {
        var entities = _storeManager.Set<T>()?.Data?.Where(predicate);
        return Task.FromResult(entities);
    }

    public void Remove(T entity)
    {
        _storeManager.Set<T>().Data.Remove(entity);
    }

    public void RemoveRange(T entities)
    {

    }
}

public class UserRepository : GenericMemoryRepository<User>, IUserRepository
{
    public UserRepository(IStoreManager manager)
    : base(manager)
    {
    }
}

That’s all we need to define for our data  layer for now. Next let’s look at our business logic layer and how it interacts with the data layer through references to our domain interfaces.

Infrastructure.Business

Our business layer is our implementation of our Application layer. So we are going to implement the IBaseService and IUserService we defined in the previous segment:

IBaseService.cs and IUserService.cs

public class BaseService : IBaseService
{
    public BaseService()
    {
    }

    public IEnumerable<string> Validate(object model)
    {
        if(model == null)
            return new List<string> { "Empty model received" };
        return null;
    }
}

public class UserService : BaseService, IUserService
{
    private readonly IUserRepository _userRepository;
    public UserService(IUserRepository userRepository)
    {
        _userRepository = userRepository;
    }
    public async Task<Result<UserTransferObject>> CreateUserAsync(NewUser model)
    {
        var errors = Validate(model);
        if (errors == null)
        {
            var entity = model.ToUser();
            _userRepository.Add(entity);
            await _userRepository.CommitAsync();

            return new Result<UserTransferObject>(new UserTransferObject(entity));
        }
        return new Result<UserTransferObject>(ResultType.Invalid, errors);
    }

    public async Task<Result<UserTransferObject>> FindByIdAsync(int userId)
    {
        var entity = await _userRepository.FindAsync(user => user.Id == userId);
        if (entity == null)
        {
            return new Result<UserTransferObject>(ResultType.Failed, "Could not find user with this Id");
        }
        return new Result<UserTransferObject>(new UserTransferObject(entity));
    }

    public async Task<Result<UserTransferObject>> RemoveByIdAsync(int userId)
    {
        var entity = await _userRepository.FindAsync(user => user?.Id == userId);
        if (entity == null)
        {
            return new Result<UserTransferObject>(ResultType.Failed, "Could not find user with this Id");
        }
        _userRepository.Remove(entity);
        await _userRepository.CommitAsync();
        return new Result<UserTransferObject>(new UserTransferObject(entity));
    }

    public async Task<Result<IEnumerable<UserTransferObject>>> GetValidUsers()
    {
        var entities = await _userRepository.GetAsync(user =>         !string.IsNullOrEmpty(user?.Email));
        return new Result<IEnumerable<UserTransferObject>>(entities?.Select(entity => new UserTransferObject(entity)));
    }
}

The biggest thing to point out is how the constructor for our UserService takes in an IUserRepository. Later we will set up our IoC container and inject our actual UserService so that the logic ties together. Doing this allows us to avoid referencing the Infrastructure.Data layer in our Infrastructure.Business layer which gives us full Separation of Concerns in our layers.

What’s Next

In the next segment, we’ll talk about implementing our Xamarin.Forms application, setting up our Inversion of Control and Dependency Injection, and tying it all together.

We’ll also look at each of our different platforms and talk about how we can utilize them without using Xamarin.Forms.

Finally, in the last segment, we will talk about how to truly utilize the Onion Architecture to test, pull, and change important pieces of our application without having to touch anything else.

 

Check out Part 4 to look at the Client Layer

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Organized Architecture for a Cross-Platform SignalR Application

SignalR is a great tool for keeping not only your web applications synced in real-time, but with it’s easy to use APIs for clients, it is perfect for use in your mobile applications.

I have some previous posts that are going to help in designing the of an architecture for a cross-platform implementation with SignalR. Take a look at these:

In this scenario, we are going to focus on two major layers of separation within our applications, although you can always add more layers of abstraction if that is your style or preference. Our two layers are the Portable Class Library and Native Client Libraries. This example is going to be using one PCL with all of our shared code, and then individual projects for Windows Phone 8.1, Windows 8.1, Xamarin.iOS, and Xamarin.Android.

The Portable Class Library

In this architecture, we want to focus on sharing as much code as possible. This implies that the only code that should not be in our PCL is code that includes the UI (Note we are not using Xamarin.Forms), updates the UI, or accesses the device’s native features (cameras, location, etc). This would include things such as ViewModels if you’re using the MVVM pattern (this example is using MVVM Light), Models, Web Request Logic, and even our SignalR Managers.
With that in mind, here are some nuget packages to consider for your PCL:

So let’s get started with a simple BaseHubManager to manage our connections. I’m going to follow a basic Inheritance pattern for these managers so that we can share as much of our SignalR code in our Base Manager as possible.

BaseHubManager:

  public class BaseHubManager
    {
        public HubConnection Connection{ get; set; }
        public IHubProxy Proxy { get; set; }

        // The empty constructor should only be used for a basic connection with no specific Hub
        public BaseHubManager()
        {
            Connection= new HubConnection(Constants.BaseUrl);
        }

        // Connect to specific Hub
        public BaseHubManager(string hubProxy)
        {
            Connection= new HubConnection(Constants.BaseUrl);
            Connection.Headers.Add(&quot;Authorization&quot;, string.Format(&quot;Bearer {0}&quot;, App.CurrentUser.TokenInfo.AccessToken)); //add access token to authorize
            Proxy = Connection.CreateHubProxy(hubProxy);
        }

        public async Task Start()
        {
            await _connection.Start(new LongPollingTransport());
            //Add additional shared Start logic
        }

        public void Stop()
        {
             _connection.Stop();
             //Add additional shared Stop logic
        }

        public virtual async void Connect()
        {
            await this.Start();
            //Add additional shared Connect logic
        }
    }

Now that we have a solid base, we can easily spin up individual Hub managers to connect to specific Hubs. Below is an example of a HubManager that would connect to the “ChatHub” on your server.

ChatHubManager:

 public class ChatHubManager : BaseHubManager
    {
        public ObservableCollection&lt;string&gt; Messages{ get; set; }

        public ChatHubManager ()
            : base(&quot;ChatHub&quot;)
        {
            this.Connect();
        }
        // Send new message to ChatHub
        public async Task&lt;string&gt; Create(string newMessage)
        {
            //establish connection
            await this.Start();

            var message= await Proxy.Invoke&lt;string&gt;(&quot;Create&quot;, newMessage);

            return message;
        }

        // Get all messages from ChatHub
        public async Task&lt;IEnumerable&lt;string&gt;&gt; Get()
        {
            //establish connection
            await this.Start();

            var messages = await Proxy.Invoke&lt;IEnumerable&lt;string&gt;&gt;(&quot;Get&quot;));

            Messages = new ObservableCollection&lt;string&gt;(messages);
            return messages;

        }

    }

Expanding new HubManagers like this one make it very easy to call server-side methods from our client by simply creating an instance of our Manager and calling our Invoking methods:

var manager = new ChatManager();
var messages = await manager.Get();

Now what about the other side of SignalR – Client methods? There are some things to consider. Most importantly, will your client end points update anything in the UI? This also includes updating ViewModel properties that will cause updates in the UI.
The problem is that the client end point listeners don’t stem from any sort of UI action the way that calling a server method might. Thus, it can’t run on the UI thread by itself and you would likely run into some sort of Threading Exception.

If you don’t need to update the UI at any point from your client listener, consider adding your listeners in your manager with something like this:

public ChatHubManager ()
    : base(&quot;ChatHub&quot;)
{
        this.Connect();
        Proxy.On&lt;string&gt;(&quot;newMessage&quot;, async data =&gt;
        {
            //Do something that is NOT on the UI thread
        }
}

One thing that SignalR does wonderfully is give you the ability to add these listeners from anywhere. That includes from your individual client projects that reference your PCL. So, let’s look at how to add these kind of requests to our client projects so we can update our UIs.

The Individual Client Projects

Let’s use a Windows Phone 8.1 project as our example, although the same logic can be applied to any type of project. So we need to add our client listener like we did above, but we also need it to make changes to our UI, which will require tapping into our UI thread. For this case, let’s add a ChatSignalingManager to our Windows Phone project that contains a reference to our ChatHubManager in our PCL above:

 public class ChatSignalingManager
    {
        private ChatHubManager _hubManager;
        private CoreDispatcher _dispatcher;
        public ChatSignalingManager (CoreDispatcher dispatcher)
        {
            _hubManager= new ChatHubManager ();
            _dispatcher = dispatcher;
            InitializeChatEndpoints();
        }

       //Add client end points for the ChatHubManager
        private void InitializeChatEndpoints()
        {
            var newMessage = _hubManager.Proxy.On&lt;string&gt;(&quot;newMessage&quot;, async data =&gt;
            {
                await _dispatcher.RunAsync(Windows.UI.Core.CoreDispatcherPriority.Normal, () =&gt;
                    {
                        // process your UI changes here
                    });
            });

           // Add additional end points for the ChatHub here
        }

    }

Notice the biggest difference in how we handle our end point in our client project versus our PCL. The Dispatcher. In this case, we can pass Windows CoreDispatcher to our constructor, and by calling _dispatcher.RunAsync we are able to execute our process on our UI thread to successfully run code against our UI.

Here is an example of constructing the ChatSignalingManager from the MainPage of a Windows Phone app:

public sealed partial class MainPage : Page
{

    private ChatSignalingManager _signalingManager;
    public MainPage()
    {
        this.InitializeComponent();

        this.NavigationCacheMode = NavigationCacheMode.Required;
        _signalingManager = new ChatSignalingManager (Dispatcher);

    }

}

Hopefully that is enough code to get you started, but feel free to ask more questions in the comments. Just remember to share as much code as possible in your PCL and use your Client Projects to handle updates to your UI and also to utilize SignalR’s flexibility and versatility.