MCT architecture

Overview

Today we've two projects on our repo, they are the Core and Maui projects, which will be called Controls in this article.

This architecture was idealized to follow the .NET MAUI architecture, having a better separation and allowing the code to be used by other flavors of Toolkits. Our toolkit is based on the MVVM flavor, but we can have toolkits around Blazor, Comet, and any other flavor of .NET MAUI that can be created in the future. To understand this idea better let's take a look into each project and its responsibilities.

If you want to have more context around the conversion of this structure you can see #213. You can see the general architecture in the image below.

Core

The Core project has all the agnostic code in our lib, it shouldn't be opinionated, so any other project that can take reference on it can implement its own style and opinions. To make it clear see this wrong example around a Button control, that's a universal concept.

public interface IButton
{
	ICommand ClickCommand;
	EventHandler Clicked;
}

That's wrong because ICommand is a pattern followed by MVVM and Reactive, for example, doesn't have that concept. In the second we have an EventHandler for the Clicked action, again we're forcing the implementor to use an EventHandler and that can break the desired pattern. So what will be the solution? Well pretty simple, we will use something that's common for all C# vanilla approaches.

public interface IButton
{
	void OnClick();
}

So we just use a void method to represent the Click action, with that the implementor can abstract it on their desired pattern, doesn't matter if it's a Command, an event, or any other pattern. So keep that in mind if you need to implement something on the Core project.

Also, on Core we add the primitive values, like structs, EventArgs, Handlers, and Platform controls that will be used by Handlers.

In order to keep the Core project even more agnostic we don't use the Microsoft.Maui.Controls namespace. The explanation is very simple, everything on this namespace is MVVM opinionated so doesn't make sense to use it on our Core project. So, if you need to depend on something that lives on the Microsoft.Maui.Controls namespace it shouldn't be on Core.

To finish on this subject, the Core project is our layer that is intended to be used by other libraries.

Controls

The Controls project is where all opinionated implementation lives, talking about this toolkit that's MVVM opinionated, all the code will have that in mind, and, of course, we can use the Microsoft.Maui.Controls namespace.

This project implements the Core abstractions, so we create the shared controls and connect them to the respective handler, and we can extend the handler by adding features that will not suit the Core layer, for example, something that's platform-specific or something that we feel that isn't needed for all flavors of .NET MAUI.

On the Controls project we implement also some concepts that also just exist in the Microsoft.Maui.Controls namespace, like Behaviors, PlatformBehaviors, Converters etc. Those shouldn't be on Core since they can't exist in other .NET MAUI flavors.

In the snippet below you can see an example of an implementation of the IButton interface defined on Core.

public Button : View, IButton
{
	public static readonly BindableProperty ClickCommandProperty = 
		BindableProperty.Create(nameof(ClickCommand), typeof(ICommand), typeof(Button));

	public ICommand ClickCommand
	{
		get => (ICommand)GetValue(ClickCommandProperty);
		set => SetValue(ClickCommandProperty, value);
	}

	IButton.OnClick()
	{
		ClickCommand?.Invoke();
	}
}

So as you can see, here we take advantage of the Bindings structure and the ICommand concept that's very MVVM opinionated.