winforms

name winforms description Build, maintain, or modernize Windows Forms applications with practical guidance on designer-driven UI, event handling, data binding, MVP separation, and migration to modern .NET. USE FOR: 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. DO NOT USE FOR: unrelated stacks; generic tasks that do not need this specific guidance. INVOKES: inspect the repository context, edit targeted files, and run relevant build, test, lint, or validation commands when changes are made. compatibility Requires a Windows Forms project on .NET or .NET Framework. 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 Respect designer boundaries — never edit .Designer.cs directly; changes are lost on regeneration. 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); } }; } } 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>()); Use data binding via BindingSource and INotifyPropertyChanged instead of manual control population. See references/patterns.md for complete binding patterns. Use async/await for I/O operations — disable controls during loading, use Progress<T> for progress reporting. Never block the UI thread. Validate with ErrorProvider and the Validating event. Call ValidateChildren() before save operations. Modernize incrementally — prefer better structure over big-bang rewrites. Use .NET 8+ features (button commands, stock icons) when available. Current Upstream Notes The August 2026 Windows Forms overview remains focused on Windows desktop, designer-driven controls, events, data binding, and migration to modern .NET. It does not change the framework-selection guidance: improve form boundaries and designer safety before proposing a rewrite. For docs-driven updates, validate whether the app targets .NET Framework, modern .NET, or mixed libraries before changing project format, designer files, or deployment assumptions. 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"] Key Decisions Decision Guidance MVP vs MVVM Prefer MVP for WinForms — simpler with event-driven model BindingSource vs manual Always prefer BindingSource for list/detail binding Sync vs async I/O Always async — use async void only for event handlers Custom controls Extract reusable UserControl when form grows beyond ~300 lines .NET Framework → .NET Use the official migration guide; validate designer compatibility first 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 references/patterns.md - WinForms architectural patterns (MVP, MVVM, Passive View), data binding, validation, form communication, threading, DI setup, and .NET 8+ features references/migration.md - step-by-step migration from .NET Framework to modern .NET, common issues, deployment options, and gradual migration strategies