Xamarin - ViewModel with constructor with parameters as Binding Context in Xaml

Question

I have a simple issue. I'm trying to create my cross-platform app in xamarin, here's the scenario.

I have a page, and on it a list of accommodations. My idea is that when I click an accommodation, it opens a new page with more details about it. It's covered with this event:

private void ListView_ItemTapped(object sender, ItemTappedEventArgs e)
{
    var Odabrani = e.Item;

    PropertyInfo pi = Odabrani.GetType().GetProperty("SmjestajId");
    int id = Convert.ToInt32(pi.GetValue(Odabrani,null).ToString());
    Application.Current.MainPage = new SmjestajViewPage(id);
}

SmjestajViewPage would be the Page that is opened, and obviously I need that accommodation's Id to fetch the relevant information about it. This works fine, I'm getting the right id.

This is what I have so far for the xaml.cs file:

[XamlCompilation(XamlCompilationOptions.Compile)]
public partial class SmjestajViewPage : ContentPage
{
    private int _Id;
    SmjestajVM viewmodel = null;
    public SmjestajViewPage()
    {
        InitializeComponent();
    }

    public SmjestajViewPage(int id)
    {
        InitializeComponent();
        _Id = id;
        BindingContext = viewmodel = new SmjestajVM(id);           
    }
}

This is how SmjestajVM looks so far:

public class SmjestajVM : BaseViewModel
{
    int _SmjestajId;
    public SmjestajVM(int Id)
    {
        _SmjestajId = Id;
    }

}

However, unless I add a parameter-less constructor, this option does not appear as one of the options in the xaml editing process. This is how my xaml file looks so far:

<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:d="http://xamarin.com/schemas/2014/forms/design"
             xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
             xmlns:ViewModels="clr-namespace:RS2_Booking.MobileApp.ViewModels"
             mc:Ignorable="d"
             x:Class="RS2_Booking.MobileApp.Views.SmjestajViewPage"
            >
    <ContentPage.BindingContext>
        <ViewModels:SmjestajVM></ViewModels:SmjestajVM>
    </ContentPage.BindingContext>
    <ContentPage.Content>
        <StackLayout>
            <Label Text="Welcome to Xamarin.Forms!"
                VerticalOptions="CenterAndExpand" 
                HorizontalOptions="CenterAndExpand" />
        </StackLayout>
    </ContentPage.Content>
</ContentPage>

The issue is with this line:

  <ContentPage.BindingContext>
        <ViewModels:SmjestajVM></ViewModels:SmjestajVM>
    </ContentPage.BindingContext>

How do I write this so it works properly? I tried SmjestajVM(Id) and SmjestajVM("Id") but neither worked.

you can't do that in XAML with vanilla XF. You either need to do it in the code-behind, or use an MVVM framework — Jason, Dec 20 '19 at 02:27

score 0 · Answer 1 · answered Dec 20 '19 at 05:59

I don't think you can do that in xaml, there is no such syntax in Xamarin.forms. What you did so far is right.

Or you can set the BindingContext in xaml:

  <ContentPage.BindingContext>
        <ViewModels:SmjestajVM></ViewModels:SmjestajVM>
  </ContentPage.BindingContext>

and then can get the bindingContext in code behind and set id:

public partial class MainPage : ContentPage
{

    private int _Id;
    public MainPage()
    {
        InitializeComponent();

        SmjestajVM m = this.BindingContext as SmjestajVM;
        m.SmjestajId = _Id;
    }
}


public class SmjestajVM
{
    public int _SmjestajId { get; set; }

    public int SmjestajId
    {
        set
        {
            _SmjestajId = value;

            updateViewModel();
        }
        get
        {
            return _SmjestajId;
        }
    }

    public SmjestajVM()
    {
    }

    public void updateViewModel(){

    }
}

You can also have a look at this thread for more information.

Xamarin - ViewModel with constructor with parameters as Binding Context in Xaml

1 Answers1