Implementeer ICommand patroon met RelayCommand voor MVVM

- Voeg RelayCommand class toe voor herbruikbare ICommand implementatie
- Vervang button click event handler door AddProductCommand in MainViewModel
- Update XAML om Command binding te gebruiken in plaats van Click event
- Verwijder business logic uit code-behind (MainWindow.xaml.cs)
- Los DataContext duplicatie op (was twee keer MainViewModel instantie)

Dit maakt de applicatie beter testbaar en volgt proper MVVM principes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

ViewModels/MainViewModel.cs

@@ -5,6 +5,8 @@ using System.ComponentModel;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
+using System.Windows.Input;
+using MVVM_DEMO.Commands;
 using MVVM_DEMO.Models;
 
 namespace MVVM_DEMO.ViewModels
@@ -28,6 +30,9 @@ namespace MVVM_DEMO.ViewModels
         {
             _products = new ObservableCollection<Product>();
             LoadData();
+
+            // Initialize commands
+            AddProductCommand = new RelayCommand(ExecuteAddProduct, CanExecuteAddProduct);
         }
 
         // read data
@@ -46,5 +51,28 @@ namespace MVVM_DEMO.ViewModels
         public string productName { get; set; }
         public int productPrice { get; set; }
 
+        // Commands
+        public ICommand AddProductCommand { get; set; }
+
+        // Command methods
+        private void ExecuteAddProduct(object? parameter)
+        {
+            Random random = new Random();
+            int randomPrice = random.Next(10, 100);
+
+            Products.Add(new Product
+            {
+                ProductName = $"Product {Products.Count + 1}",
+                Price = randomPrice
+            });
+        }
+
+        private bool CanExecuteAddProduct(object? parameter)
+        {
+            // You can add validation logic here
+            // For now, always allow adding products
+            return true;
+        }
+
     }
 }