如何在ViewModel中使用来自后面代码的对象

Question

I have a set of pages between which I navigate and between which I need to pass some parameters, namely some objects of the type of my Models. When I navigate to a page I Setup this new page's constructor with a parameter of the type of the object I need, so the class is implemented as follows:

public partial class ArtigoEdit : ContentPage
{
    EditionsViewModel viewModel;
    public ArtigoEdit(Models.Artigo artigo)
    {
        InitializeComponent();

        BindingContext = viewModel = new EditionsViewModel();

        this.viewModel.Artigo = artigo;
    }
}

As you can see I'm also using the MVVM pattern and on its side I have a variable "Artigo" to which I want to assign the object my constructor receives:

Models.Artigo artigo;
public Models.Artigo Artigo
{
    get { return artigo; }
    set { artigo = value; this.Notify("Artigo"); }
}

The problem is that if I try to access the attributes of this object in order to change the way they are displayed and bind to these new variables instead the object is null when the page opens so the variables are not shown:

string tipoArtigo = "";
public string TipoArtigo
{
    get { return tipoArtigo; }
    set 
    { 
        if (Artigo != null)
        {
            if(Artigo.TipoArtigo == "P")
                tipoArtigo = "Produto";
            else if (Artigo.TipoArtigo == "S")
                tipoArtigo = "Serviço";
            else if (Artigo.TipoArtigo == "O")
                tipoArtigo = "Outro";
            else if (Artigo.TipoArtigo == "I")
                tipoArtigo = "Imposto";
            else
                tipoArtigo = value;
        }
        this.Notify("TipoArtigo"); 
    }
}

Is this not the correct way of doing this? If not, what is my alternative? Beware that my ViewModels all implemente a ViewModelBase class that itself implements INotifyPropertyChanged so do not worry about that! :)

Answer 1

Silly me, I'm sorry for disturbing and I thank to all the people who tried to help. What was happening was: I was binding these variables to an Entry, but for some reason it was not expanding to fit the size of information so although it was there it did not appear to be...luckily I've noticed it.