FreshMvvm for Xamarin.Forms

FreshMvvm is a super light Mvvm Framework designed specifically for Xamarin.Forms. It's designed to be Easy, Simple and Flexible.

How does it compare to other options?

• It's super light and super simple
• It's specifically designed for Xamarin.Forms
• Designed to be easy to learn and develop (great when you are not ready for RxUI)
• Uses a Convention over Configuration

Features

• PageModel to PageModel Navigation
• Automatic wiring of BindingContext
• Automatic wiring of Page events (eg. appearing)
• Basic methods (with values) on PageModel (init, reverseinit)
• Built in IOC Container
• PageModel Constructor Injection
• Basic methods available in Model, like Alert
• Built in Navigation types for SimpleNavigation, Tabbed and MasterDetail

Note Different to standard naming conventions, FreshMvvm uses Page and PageModel instead of View and ViewModel, this is inline with Xamarin.Forms using Pages Now we can use both the ViewModel naming conventions.

The Story

I (Michael Ridland) was part-way into a Xamarin Traditional application when Xamarin.Forms was released. I wanted to move the project onto Xamarin.Forms but on that project I was using MvvmCross. At that time MvvmCross had no support for Xamarin.Forms, so I had the option of 1) adapting MvvmCross, 2) finding an alternative or 3) rolling my own Mvvm. The best part about MvvmCross was it's two-way databinding to the native iOS/Android controls but since Xamarin.Forms already had the Databinding builtin, that wasn't useful and the size with MvvmCross was an overhead when I didn't require it. I also wasn't able to find an alternative that I could easily move to. So that I could keep it simple and flexible, I ended up rolling my own Mvvm.

It's grown up from this post on rolling your own Mvvm for Xamarin.Forms. I try hard to keep the simplicity of rolling your own Mvvm for Xamarin.Forms.

It was never a plan to create a framework but after presenting my Mvvm solution at a few events, I found many people wanted it and seemed to be really interested in it. Also considering I've been using this Framework in all my projects from the start of Xamarin.Forms I know that it works, so I created FreshMvvm and that's how it was born.

Conventions

This Framework, while simple, is also powerful and uses a Convention over Configuration style.

Note Different to standard naming conventions, FreshMvvm uses Page and PageModel instead of View and ViewModel, this is inline with Xamarin.Forms using Pages Now we can use both the ViewModel naming conventions.

• A Page must have a corresponding PageModel, with naming important so a QuotePageModel must have a QuotePage The BindingContext on the page will be automatically set with the Model
• A PageModel can have a Init method that takes a object
• A PageModel can have a ReverseInit method that also take a object and is called when a model is poped with a object
• PageModel can have dependancies automatically injected into the Constructor

Navigation

The Primary form of Navigation in FreshMvvm is PageModel to PageModel, this essentially means our views have no idea of Navigation.

So to Navigate between PageModels use:

await CoreMethods.PushPageModel<QuotePageModel>(); // Pushes navigation stack
await CoreMethods.PushPageModel<QuotePageModel>(null, true); // Pushes a Modal

The engine for Navigation in FreshMvvm is done via a simple interface, with methods for Push and Pop. Essentially these methods can control the Navigation of the application in any way they like.

public interface IFreshNavigationService
{
	Task PushPage(Page page, FreshBasePageModel model, bool modal = false);
	Task PopPage(bool modal = false);
}

Within the PushPage and PopPage you can do any type of navigation that you like, this can from a simple navigation to a advanced nested navigation.

The Framework contains some built in Navigation containers for the different types of Navigation.

Basic Navigation - Built In

var page = FreshPageModelResolver.ResolvePageModel<MainMenuPageModel> ();
var basicNavContainer = new FreshNavigationContainer (page);
MainPage = basicNavContainer;

Master Detail - Built In

var masterDetailNav = new FreshMasterDetailNavigationContainer ();
masterDetailNav.Init ("Menu");
masterDetailNav.AddPage<ContactListPageModel> ("Contacts", null);
masterDetailNav.AddPage<QuoteListPageModel> ("Pages", null);
MainPage = masterDetailNav;

Tabbed Navigation - Built In

var tabbedNavigation = new FreshTabbedNavigationContainer ();
tabbedNavigation.AddTab<ContactListPageModel> ("Contacts", null);
tabbedNavigation.AddTab<QuoteListPageModel> ("Pages", null);
MainPage = tabbedNavigation;

Implementing Custom Navigation

It's possible to setup any type of Navigation by implementing IFreshNavigationService.There's a sample of this in Sample Application named CustomImplementedNav.cs.

Sample Apps

• Basic Navigation Sample
• Tabbed Navigation Sample
• MasterDetail Navigation Sample
• Tabbed Navigation with MasterDetail Popover Sample (This is called the CustomImplementedNav in the Sample App)

Inversion of Control (IOC)

So that you don't need to include your own IOC container, FreshMvvm comes with a IOC container built in. It's using TinyIOC underneith, but with different naming to avoid conflicts.

To Register services in the container use Register:

FreshIOC.Container.Register<IDatabaseService, DatabaseService>();

To obtain a service use Resolve:

FreshIOC.Container.Resolve<IDatabaseService>();

*This is also what drives constructor injection.

IOC Container Lifetime Registration Options

We now support a fluent API for setting the object lifetime of object inside the IOC Container.

// By default we register concrete types as 
// multi-instance, and interfaces as singletons
FreshIOC.Container.Register<MyConcreteType>(); // Multi-instance
FreshIOC.Container.Register<IMyInterface, MyConcreteType>(); // Singleton 

// Fluent API allows us to change that behaviour
FreshIOC.Container.Register<MyConcreteType>().AsSingleton(); // Singleton
FreshIOC.Container.Register<IMyInterface, MyConcreteType>().AsMultiInstance(); // Multi-instance

As you can see below the IFreshIOC interface methods return the IRegisterOptions interface.

public interface IFreshIOC
{
    object Resolve(Type resolveType);
    IRegisterOptions Register<RegisterType>(RegisterType instance) where RegisterType : class;
    IRegisterOptions Register<RegisterType>(RegisterType instance, string name) where RegisterType : class;
    ResolveType Resolve<ResolveType>() where ResolveType : class;
    ResolveType Resolve<ResolveType>(string name) where ResolveType : class;
    IRegisterOptions Register<RegisterType, RegisterImplementation> ()
        where RegisterType : class
        where RegisterImplementation : class, RegisterType;
}

The interface that's returned from the register methods is IRegisterOptions.

public interface IRegisterOptions
{
    IRegisterOptions AsSingleton();
    IRegisterOptions AsMultiInstance();
    IRegisterOptions WithWeakReference();
    IRegisterOptions WithStrongReference();
    IRegisterOptions UsingConstructor<RegisterType>(Expression<Func<RegisterType>> constructor);
}

PageModel - Constructor Injection

When PageModels are pushed services that are in the IOC container can be pushed into the Constructor.

FreshIOC.Container.Register<IDatabaseService, DatabaseService>();

PageModel Important Methods

/// <summary>
/// The previous page model, that's automatically filled, on push
/// </summary>
public FreshBasePageModel PreviousPageModel { get; set; }

/// <summary>
/// A reference to the current page, that's automatically filled, on push
/// </summary>
public Page CurrentPage { get; set; }

/// <summary>
/// Core methods are basic built in methods for the App including Pushing, Pop and Alert
/// </summary>
public IPageModelCoreMethods CoreMethods { get; set; }    

/// <summary>
/// This method is called when a page is Pop'd, it also allows for data to be returned.
/// </summary>
/// <param name="returndData">This data that's returned from </param>
public virtual void ReverseInit(object returndData) { }

/// <summary>
/// This method is called when the PageModel is loaded, the initData is the data that's sent from pagemodel before
/// </summary>
/// <param name="initData">Data that's sent to this PageModel from the pusher</param>
public virtual void Init(object initData) { }

/// <summary>
/// This method is called when the view is disappearing. 
/// </summary>
protected virtual void ViewIsDisappearing (object sender, EventArgs e)
{
}

/// <summary>
/// This methods is called when the View is appearing
/// </summary>
protected virtual void ViewIsAppearing (object sender, EventArgs e)
{
}

The CoreMethods

Each PageModel has a property called 'CoreMethods' which is automatically filled when a PageModel is pushed, it's the basic functions that most apps need like Alerts, Pushing, Poping etc.

public interface IPageModelCoreMethods
{
	Task DisplayAlert (string title, string message, string cancel);
	Task<string> DisplayActionSheet (string title, string cancel, string destruction, params string[] buttons);
	Task<bool> DisplayAlert (string title, string message, string accept, string cancel);
	Task PushPageModel<T>(object data, bool modal = false) where T : FreshBasePageModel;
	Task PopPageModel(bool modal = false);
	Task PopPageModel(object data, bool modal = false);
	Task PushPageModel<T>() where T : FreshBasePageModel;
}

Page important methods

PageModel Init PropertyChanged

Sample PageModel

[ImplementPropertyChanged] // Use Fody for Property Changed Notifications
public class QuoteListPageModel : FreshBasePageModel
{
	IDatabaseService _databaseService;
	
	//These are automatically filled via Constructor Injection IOC
	public QuoteListPageModel (IDatabaseService databaseService) 
	{
		_databaseService = databaseService;
	}
	
	public ObservableCollection<Quote> Quotes { get; set; }
	
	public override void Init (object initData)
	{
		Quotes = new ObservableCollection<Quote> (_databaseService.GetQuotes ());
	}
	
	//The Framework support standard functions list appeaing and disappearing
	protected override void ViewIsAppearing (object sender, System.EventArgs e)
	{
		CoreMethods.DisplayAlert ("Page is appearing", "", "Ok");
		base.ViewIsAppearing (sender, e);
	}
	
	protected override void ViewIsDisappearing (object sender, System.EventArgs e)
	{
		base.ViewIsDisappearing (sender, e);
	}

	//This is called when a pushed Page returns to this Page
	public override void ReverseInit (object value)
	{
		var newContact = value as Quote;
		if (!Quotes.Contains (newContact)) {
			Quotes.Add (newContact);
		}
	}

	public Command AddQuote {
		get {
			return new Command (async () => {
				//Push A Page Model
				await CoreMethods.PushPageModel<QuotePageModel> ();
			});
		}
	}

	Quote _selectedQuote;

	public Quote SelectedQuote {
		get {
			return _selectedQuote;
		}
		set {
			_selectedQuote = value;
			if (value != null)
				QuoteSelected.Execute (value);
		}
	}

	public Command<Quote> QuoteSelected {
		get {
			return new Command<Quote> (async (quote) => {
				await CoreMethods.PushPageModel<QuotePageModel> (quote);
			});
		}
	}
}

Multiple Navigation Services

It’s always been possible to do any type of navigation in FreshMvvm, with custom or advanced scenarios were done by implementing a custom navigation service. Even with this ability people found it a little hard to do advanced navigation scenarios in FreshMvvm. After I reviewed all the support questions that came in for FreshMvvm I found that the basic issue people had was they wanted to be able to use our built in navigation containers multiple times, two primary examples are 1) within a master detail having a navigation stack in a master and another in the detail 2) The ability to push modally with a new navigation container. In order to support both these scenarios I concluded that the FreshMvvm required the ability to have named NavigationServices so that we could support multiple NavigationService’s.

Using multiple navigation containers

Below we’re running two navigation stacks, in a single MasterDetail.

var masterDetailsMultiple = new MasterDetailPage (); //generic master detail page

//we setup the first navigation container with ContactList
var contactListPage = FreshPageModelResolver.ResolvePageModel<ContactListPageModel> ();
contactListPage.Title = "Contact List";
//we setup the first navigation container with name MasterPageArea
var masterPageArea = new FreshNavigationContainer (contactListPage, "MasterPageArea");
masterPageArea.Title = "Menu";

masterDetailsMultiple.Master = masterPageArea; //set the first navigation container to the Master

//we setup the second navigation container with the QuoteList 
var quoteListPage = FreshPageModelResolver.ResolvePageModel<QuoteListPageModel> ();
quoteListPage.Title = "Quote List";
//we setup the second navigation container with name DetailPageArea
var detailPageArea = new FreshNavigationContainer (quoteListPage, "DetailPageArea");

masterDetailsMultiple.Detail = detailPageArea; //set the second navigation container to the Detail

MainPage = masterDetailsMultiple;

PushModally with new navigation stack

//push a basic page Modally
var page = FreshPageModelResolver.ResolvePageModel<MainMenuPageModel> ();
var basicNavContainer = new FreshNavigationContainer (page, "secondNavPage");
await CoreMethods.PushNewNavigationServiceModal(basicNavContainer, new FreshBasePageModel[] { page.GetModel() }); 

//push a tabbed page Modally
var tabbedNavigation = new FreshTabbedNavigationContainer ("secondNavPage");
tabbedNavigation.AddTab<ContactListPageModel> ("Contacts", "contacts.png", null);
tabbedNavigation.AddTab<QuoteListPageModel> ("Quotes", "document.png", null);
await CoreMethods.PushNewNavigationServiceModal(tabbedNavigation);

//push a master detail page Modally
var masterDetailNav = new FreshMasterDetailNavigationContainer ("secondNavPage");
masterDetailNav.Init ("Menu", "Menu.png");
masterDetailNav.AddPage<ContactListPageModel> ("Contacts", null);
masterDetailNav.AddPage<QuoteListPageModel> ("Quotes", null);
await CoreMethods.PushNewNavigationServiceModal(masterDetailNav);

Switching out NavigationStacks on the Xamarin.Forms MainPage

There's some cases in Xamarin.Forms you might want to run multiple navigation stacks. A good example of this is when you have a navigation stack for the authentication and a stack for the primary area of your application.

To begin with we can setup some names for our navigation containers.

public class NavigationContainerNames
{
    public const string AuthenticationContainer = "AuthenticationContainer";
    public const string MainContainer = "MainContainer";
}

Then we can create our two navigation containers and assign to the MainPage.

var loginPage = FreshMvvm.FreshPageModelResolver.ResolvePageModel<LoginViewModel>();
var loginContainer = new FreshNavigationContainer(loginPage, NavigationContainerNames.AuthenticationContainer);

var myPitchListViewContainer = new MainTabbedPage(NavigationContainerNames.MainContainer);

MainPage = loginContainer;

Once we've set this up we can now switch out our navigation containers.

CoreMethods.SwitchOutRootNavigation(NavigationContainerNames.MainContainer);

Custom IOC Containers

The second major request for FreshMvvm 1.0 was to allow custom IOC containers. In the case that your application already has a container that you want to leverage.

Using a custom IOC container is very simple in that you only need to implement a single interface.

public interface IFreshIOC
{
    object Resolve(Type resolveType);
    void Register<RegisterType>(RegisterType instance) where RegisterType : class;
    void Register<RegisterType>(RegisterType instance, string name) where RegisterType : class;
    ResolveType Resolve<ResolveType>() where ResolveType : class;
    ResolveType Resolve<ResolveType>(string name) where ResolveType : class;
    void Register<RegisterType, RegisterImplementation> ()
        where RegisterType : class
        where RegisterImplementation : class, RegisterType;

And then set the IOC container in the System.

FreshIOC.OverrideContainer(myContainer);

Related Videos/Quick Start Guides

FreshMvvm n=0 – Mvvm in Xamarin.Forms and Why FreshMvvm

FreshMvvm n=1 : Your first FreshMvvm Application

FreshMvvm n=2 – IOC and Constructor Injection

FreshMvvm n=3: Navigation in FreshMvvm

Implementing custom navigation in FreshMvvm for Xamarin.Forms

TDD in Xamarin Studio – Live Coding FreshMvvm