Navigation with Xamarin Forms standard MVVM

Question

I recently started studying Xamarin Forms. I have a question that can be clarified here: how to navigate between pages using MVVM? Navigation should be on vm or in the view?

Example

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
     xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
     x:Class="GeoMobile.Views.Login">
     <StackLayout>
        <Label Text="GEO Mobile" VerticalOptions="Center" HorizontalOptions="Center" />
        <Entry Text="{Binding Email}" Placeholder="Email" />
        <Entry Text="{Binding Senha}" Placeholder="Senha" />
        <Button Text="Entrar" Command="{Binding Entrar}" />
        <Button Text="Registrar" />
     </StackLayout>
</ContentPage>

Login.Cs

public partial class Login : ContentPage
{
    public Login()
    {
        InitializeComponent();
        this.BindingContext = new LoginVM(Entrar);
    }

    public async void Entrar()
    {
        Navigation.InsertPageBefore(new Master__(), this);
        await Navigation.PopAsync();
    }
}

And in my vm:

public class LoginVM : ObservableBase
{
    private string _email;

    public string Email
    {
        get { return _email; }
        protected set
        {
            _email = value;
            OnPropertyChanged();
        }
    }

    private string _senha;

    public string Senha
    {
        get { return _senha; }
        set
        {
            _senha = value;
            OnPropertyChanged();
        }
    }

    public Command Entrar { get; private set; }
    private Action loginOk;

    private void login()
    {
        //checagem antes de ir para a proxima pagina
        loginOk();
    }

    public LoginVM(Action loginOk)
    {
        this.loginOk = loginOk;
        Entrar = new Command(login);
    }
}

I got the navigation by passing an action in the vm constructor, but I need to implement another navigation for the register button, but for that I would already have to pass another action in the constructor and I believe that this would not be a good practice.

If you put navigation in the vm, the software testing process will be difficult. What is the best way to get around the problem?

Answer 1

For those who have the same difficulty as me, I found a great tutorial, worth giving a check...

http://xamarinbr.azurewebsites.net/navegacao-entre-paginas-e-display-alert-com-mvvm-e-xamarin-forms/

Answer 2

By definition I believe that navigation should be done in your VM, your View should only be used for layout purposes. Of course this is not a rule and if you need to use something in your View for any problems that are occurring in the VM, you will not let your app bugging for this, but by the standard mvvm I believe the most correct would be in your vm.

Usually I create a "service" and in my base view model I use it by dependency injection. Works well, never had problems.

I recommend this Video of Angelo Belchior , he illustrates well what I wrote above.