winforms-maintainer

WinForms Maintainer

Keep an existing WinForms app alive and healthy with small, safe, behavior-preserving changes. This is maintenance, not migration: no WPF/MAUI rewrite, no restructuring the whole form. Fix the things that actually cause crashes, hangs, and leaks in long-lived WinForms apps, and leave the rest alone.

Input — point it at your code

You don't need pasted snippets. Work from whatever target the user gives:

• A single form — MainForm.cs (grab its .Designer.cs too if control setup matters)
• A folder — a Forms/ or UI/ directory
• A whole project or solution — a .csproj / .sln or the repo root
• A GitHub URL — clone first: git clone --depth 1 <url> /tmp/repo && cd /tmp/repo

Find the WinForms code yourself with Glob/Grep/Bash instead of asking for a paste:

grep -rl "System.Windows.Forms\|: Form\|InitializeComponent" --include=*.cs <target> | grep -vi "/obj/\|/bin/"
grep -rn "new Thread\|InvokeRequired\|async void\|ShowDialog\|+= " --include=*.cs <target>

Prioritize handlers with cross-thread access, blocking calls, or leaks, and tell the user which forms you scanned.

When this runs

The user maintains a WinForms app on .NET Framework and wants a specific handler/form reviewed or fixed -- a cross-thread crash, a UI that freezes, a leak, a flaky grid. They paste a Form/UserControl or describe the symptom. If you don't have the code, ask for the handler and the .Designer.cs if control setup is relevant.

Guardrail

Do not propose rewriting to another UI stack or restructuring the form. Every change must be droppable into the existing form with minimal diff. If a real fix requires bigger surgery, describe it and let the user decide -- default to the smallest safe change.

The checklist

Apply every item. For each finding: problem -> impact -> minimal fix.

1. Cross-thread UI access (the #1 WinForms crash)

Touching a control from a non-UI thread throws InvalidOperationException ("Cross-thread operation not valid").

• Detect: a Thread, Task.Run, BackgroundWorker.DoWork, timer callback, or async continuation that sets .Text, .DataSource, .Items, .Enabled, etc. on a control.
• Fix (modern): prefer async/await -- do the work with await Task.Run(...) and update the UI after the await, which resumes on the UI thread via the sync context. No Invoke needed.
• Fix (when you must marshal): if (control.InvokeRequired) control.BeginInvoke(() => control.Text = value); else control.Text = value;. Prefer BeginInvoke (async, won't deadlock) over Invoke (sync, can deadlock if the UI thread is waiting on your worker).