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); } }; } } ```

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

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

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

flowchart LR
  A["Form event"] --> B["Presenter handles logic"]
  B --> C["Service layer / data access"]
  C --> D["Update view via interface"]
  D --> E["Validate and display results"]

Deliver

• less brittle form code with clear UI/logic separation
• MVP pattern with testable presenters
• pragmatic modernization guidance for WinForms-heavy apps
• data binding and validation patterns that reduce manual wiring

Validate

• designer files stay stable and are not hand-edited
• forms are not acting as the application service layer
• async operations do not block the UI thread
• validation is implemented consistently with ErrorProvider
• Windows-only runtime behavior is tested on target

References

Related skills