Tag: how-to

Microsoft.AspNetCore.OpenApi only marks a response nullable when the action returns a bare T? (and, on .NET 10, not even Task<T?>). ActionResult<T?> and IActionResult lose the annotation on both .NET 10 and .NET 11 RC2. Here is why, a tested operation transformer that fixes it, and the 204 No Content trap that makes the spec lie unless you also change MVC's formatter.

Subclass ThemeExtension, register one instance per ThemeData through the extensions list, read it with Theme.of(context).extension<T>(), and write a real lerp so MaterialApp's AnimatedTheme interpolates your tokens during a light/dark switch. Covers colors, radii, shadows, text styles and booleans, the missing-extension crash, the copyWith trap that drops every other extension, and why you need == and hashCode, all verified with widget tests on Flutter 3.44.8.

AnimatedSwitcher only transitions when Widget.canUpdate says the new child is a different widget, so Text to Text with no key just updates in place. Here is the one-line fix, where the key has to sit, why UniqueKey is a trap, the slide-direction bug caused by a static transitionBuilder, and the layout jump from the default Stack, all verified with widget tests on Flutter 3.44.8.

Android kills backgrounded Flutter apps to reclaim memory, and when the user comes back every StatefulWidget starts from scratch. Here is how to opt in with restorationScopeId, RestorationMixin and Restorable properties, restore text fields, scroll offsets and pushed routes, write a custom RestorableValue, and test it all with restartAndRestore and adb, verified on Flutter 3.44.8 and an Android 16 emulator.

FlutterError.onError only sees errors thrown inside framework callbacks. Unawaited futures, timers, streams, and code after an await go somewhere else. Here is which handler catches which error, measured on Flutter 3.44.8, and the main() setup that catches all of them, including on web.

A broadcast StreamController drops every event that fired before you subscribed. Here is a dependency-free BehaviorSubject replacement built on Stream.multi, a replayLatest() extension for existing streams, the async* shortcut that silently loses events, and the StreamBuilder initialData detail, all verified on Dart 3.12.2.

Drain the console input buffer with while (Console.KeyAvailable) Console.ReadKey(true) before you wait for a fresh key, and drain it every frame in a game loop so key repeat cannot pile up. How the buffer works on Windows and Unix in .NET 10, why held keys lag, the Unix echo trap, and FlushConsoleInputBuffer.

Use DbSet.Local.FindEntry(key) to ask the change tracker whether an entity with a given key is tracked, without a database round trip or a scan. Why Entry(entity).State lies for this question, why Find queries, and a tested AttachOrMerge helper for EF Core 10.

Drive NavigationBar.selectedIndex from StatefulNavigationShell.currentIndex, never from a setState field or a copy made in initState. Measured on Flutter 3.44.8 and go_router 18.0.2: which patterns drift on deep links, context.go and cross-branch pushes, why location-based indexes lie, and how to react to tab changes with didUpdateWidget.

Balancing groups (?<name>) and (?<-name>) turn a .NET regex capture group into a stack, so one pattern can match arbitrarily nested parentheses or <div> tags. The full pattern, how the stack works, inner-content capture with (?<inner-open>), and the gotchas verified on .NET 11 RC1: the empty-stack check, catastrophic backtracking, NonBacktracking, and mixed bracket types.