❔ "Items collection must be empty before using ItemsSource."

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WPF_LoginForm.Views
{
    /// <summary>
    /// Interaction logic for CustomerView.xaml
    /// </summary>
    public partial class CustomerView : UserControl
    {
        public CustomerView()
        {
            InitializeComponent();

            DGridCustomer.ItemsSource = CRMBaseEntities.GetContext().Customers.ToList();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {

        }
        private void BtnEdit_Click(object sender, RoutedEventArgs e)
        {

        }

        private void BtnAdd_Click(object sender, RoutedEventArgs e)
        {

        }
        private void BtnDelete_Click(object sender, RoutedEventArgs e)
        {

        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Data;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Imaging;
using System.Windows.Navigation;
using System.Windows.Shapes;

namespace WPF_LoginForm.Views
{
    /// <summary>
    /// Interaction logic for CustomerView.xaml
    /// </summary>
    public partial class CustomerView : UserControl
    {
        public CustomerView()
        {
            InitializeComponent();

            DGridCustomer.ItemsSource = CRMBaseEntities.GetContext().Customers.ToList();
        }

        private void Button_Click(object sender, RoutedEventArgs e)
        {

        }
        private void BtnEdit_Click(object sender, RoutedEventArgs e)
        {

        }

        private void BtnAdd_Click(object sender, RoutedEventArgs e)
        {

        }
        private void BtnDelete_Click(object sender, RoutedEventArgs e)
        {

        }
    }
}