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. ```csharp // 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+): ```csharp var services = new ServiceCollection(); services.AddSingleton<ICustomerService, CustomerSer...