ObservableCollection list is unable to find method AddRange

Issue

I am using Xamarin.Forms MVVM and sqlLite-net to make a Shared Mobile App.

I am getting an error bc 'AddRange' doesn't exist in ObservableCollection or I am using that function wrong.

All I want to do is to fill my ObservableCollection list. do I have to manually Add using loop? its weird ObservableCollection has a 'Add' method but no way to fill

Error: 'ObservableCollection' does not contain a definition for 'AddRange' and no accessible extension method 'AddRange' accepting a first argument of type 'ObservableCollection' could be found (are you missing a using directive or an assembly reference?)

using following refs:

using System.Collections.ObjectModel;
 using System.ComponentModel;
 using System.Runtime.CompilerServices;
 using System.Threading.Tasks;
using TestApp01_MVVM_Basic.Models;
using Xamarin.CommunityToolkit.ObjectModel;
 using Xamarin.Forms;
 using System.Collections.Specialized;
using TestApp01_MVVM_Basic.Services;
using System.Collections.Generic;
using System.Linq;

Below I am creating my ObservableCollection. I am getting my error on line: AddRange()

public ObservableCollection<ProductModel> ProductsList { get; set; }
public ProductViewModel()
    {
        ProductsList = new ObservableCollection<ProductModel>();
    }

 public async Task MyDisplayList()
    {
        var getData = ProductService.DisplayProduct();
        ProductsList.AddRange(getData);

    }

In Servies Class, I have following DisplayProduct() method. that returns a list from database

public static async Task<IEnumerable<ProductModel>> DisplayProduct()
    {
        await Init();

        var GetProduct = await db.Table<ProductModel>().ToListAsync();
        return GetProduct;
    }

Solution

What you are looking for is implemented on Xamarin community toolkit package: ObservableRangeCollection which sub-class System.Collections.ObjectModel.ObservableCollection<T>, you can use ObservableRangeCollection<ProductModel> instead of ObservableCollection<ProductModel> since the latter does not implement such method.

public ObservableRangeCollection<ProductModel> ProductsList { get; set; }
public ProductViewModel()
    {
        ProductsList = new ObservableRangeCollection<ProductModel>();
    }

 public async Task MyDisplayList()
    {
        var getData = await ProductService.DisplayProduct();
        ProductsList.AddRange(getData);

    }

public static async Task<IEnumerable<ProductModel>> DisplayProduct()
    {
        await Init();

        var GetProduct = await db.Table<ProductModel>().ToListAsync();
return await Task.FromResult(GetProduct);
    }

Answered By - Cfun