ObservableCollection<MyModel> doesn't see property

Issue

One of the properties of my model that I use in a CollectionView in my .NET MAUI app is a class. It looks like this:

public MyModel
{
   public string Name { get; set; }

   public Vehicle Car { get; set; } = new Vehicle();
}

My view model looks like this:

public class MyViewModel : BaseViewModel
{
   ObservableCollection<MyModel> data = new ObservableCollection<MyModel>();

   public ObservableCollection<MyModel> Data
   {
      get => data;
      set
      {
         if(data == value)
            return;

         data = value;
         OnPropertyChanged();
      }
   }
}

In my collection view, when I try to access one of the properties of the Car property which is a Vehicle object, I get an error that tells me that the property is not found.

<CollectionView
   Source={Binding Data}>
   <CollectionView.ItemTemplate>
      <DataTemplate>
         <StackLayout>
            <Label
               Text={Binding Car.Make} />
         </StackLayout>
      <DataTemplate>
   </CollectionView.ItemTemplate>
</CollectionView>

Any idea what could be causing this?

Solution

Based on your code,I created a demo, and it works properly on my side.

You can refer to the following code:

MyViewModel.cs

public class MyViewModel: INotifyPropertyChanged
{
    ObservableCollection<MyModel> data = new ObservableCollection<MyModel>();

    public ObservableCollection<MyModel> Data
    {
        get => data;
        set
        {
            if (data == value)
                return;

            data = value;
            OnPropertyChanged();
        }
    }

    public MyViewModel() {
        Data = new ObservableCollection<MyModel>();

        Data.Add(new MyModel { Name ="model_1", Car= new Vehicle {Make="Make1" } });
        Data.Add(new MyModel { Name = "model_2", Car = new Vehicle { Make = "Make2" } });
        Data.Add(new MyModel { Name = "model_3", Car = new Vehicle { Make = "Make3" } });
        Data.Add(new MyModel { Name = "model_4", Car = new Vehicle { Make = "Make4" } });

    }

    bool SetProperty<T>(ref T storage, T value, [CallerMemberName] string propertyName = null)
    {
        if (Object.Equals(storage, value))
            return false;

        storage = value;
        OnPropertyChanged(propertyName);
        return true;
    }

    protected void OnPropertyChanged([CallerMemberName] string propertyName = null)
    {
        PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
    }

    public event PropertyChangedEventHandler PropertyChanged;
}

Vehicle.cs

public class Vehicle
{
    public string Make { get; set; }
}

MainPage.xaml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="MauiCollectionApp.MainPage"
              xmlns:local="clr-namespace:MauiCollectionApp"
             >

    <ContentPage.BindingContext>
        <local:MyViewModel></local:MyViewModel>
    </ContentPage.BindingContext>


   <CollectionView  ItemsSource="{ Binding Data}">
                <CollectionView.ItemTemplate>
                    <DataTemplate>
                        <StackLayout>
                            <Label Text="{Binding Car.Make}" />

                </StackLayout>
                    </DataTemplate>
                </CollectionView.ItemTemplate>
   </CollectionView>

</ContentPage>

Update:

I tested your demo, there are some problems with your code.

1.define Drivers as follows:

   public ObservableCollection<Driver> Drivers { get; set; } = new ObservableCollection<Driver>();

Not：

public ObservableCollection<Driver> Drivers = new();

2.we should initialize the data in the constructor of MainPageViewModel ,so we can define MainPageViewModel.cs as follows:

   public class MainPageViewModel : ObservableObject
{
    //public ObservableCollection<Driver> Drivers = new();

    public ObservableCollection<Driver> Drivers { get; set; } = new ObservableCollection<Driver>();

    public MainPageViewModel() {

        Init();
    }

    public void Init()
    {
        var car = new Vehicle
        {
            Make = "Subaru",
            Model = "Outback",
            Year = 2019
        };
        var driver = new Driver
        {
            Name = "John Smith",
            Car = car
        };
        Drivers.Add(driver);

        car = new Vehicle
        {
            Make = "Infiniti",
            Model = "Q80",
            Year = 2014
        };
        driver = new Driver
        {
            Name = "John Doe",
            Car = car
        };
        Drivers.Add(driver);

        car = new Vehicle
        {
            Make = "BMW",
            Model = "535i",
            Year = 2011
        };
        driver = new Driver
        {
            Name = "John Doe",
            Car = car
        };
        Drivers.Add(driver);
    }
}

At the same time, remove code _vm.Init(); in method OnAppearing():

protected override void OnAppearing()
{
    base.OnAppearing();
    //_vm.Init();
}

3.add x:DataType in theVerticalStackLayout of MainPage.xaml.cs

           <CollectionView.ItemTemplate>
            <DataTemplate >
                <VerticalStackLayout x:DataType="local:Driver">
                    <Label
                        Text="{Binding Name}"
                        TextColor="Black"/>
                    <Label
                        Text="{Binding Car.Make}"
                        TextColor="Black"/>
                </VerticalStackLayout>
            </DataTemplate>
        </CollectionView.ItemTemplate>

Besides,add following code on the root of MainPage.xaml:

 xmlns:local="clr-namespace:MauiApp1"

Answered By - Jessie Zhang -MSFT