winforms

Windows Forms

Trigger On

• working on Windows Forms UI, event-driven workflows, or classic LOB applications
• migrating WinForms from .NET Framework to modern .NET
• cleaning up oversized form code or designer coupling
• implementing data binding, validation, or control customization

Workflow

1. Respect designer boundaries — never edit .Designer.cs directly; changes are lost on regeneration.
2. Separate business logic from forms — use MVP (Model-View-Presenter) pattern. Forms orchestrate UI; presenters contain logic; services handle data access.

   // View interface — forms implement this
   public interface ICustomerView
   {
       string CustomerName { get; set; }
       event EventHandler SaveRequested;
       void ShowError(string message);
   }
   
   // Presenter — testable without UI
   public class CustomerPresenter
   {
       private readonly ICustomerView _view;
       private readonly ICustomerService _service;
       public CustomerPresenter(ICustomerView view, ICustomerService service)
       {
           _view = view;
           _service = service;
           _view.SaveRequested += async (s, e) =>
           {
               try { await _service.SaveAsync(_view.CustomerName); }
               catch (Exception ex) { _view.ShowError(ex.Message); }
           };
       }
   }
   

3. Use DI from Program.cs (.NET 6+):

   var services = new ServiceCollection();
   services.AddSingleton<ICustomerService, CustomerService>();
   services.AddTransient<MainForm>();
   using var sp = services.BuildServiceProvider();
   Application.Run(sp.GetRequiredService<MainForm>());
   

4. Use data binding via BindingSource and INotifyPropertyChanged instead of manual control population. See references/patterns.md for complete binding patterns.
5. Use async/await for I/O operations — disable controls during loading, use Progress<T> for progress reporting. Never block the UI thread.
6. Validate with ErrorProvider and the Validating event. Call ValidateChildren() before save operations.
7. Modernize incrementally — prefer better structure over big-bang rewrites. Use .NET 8+ features (button commands, stock icons) when available.