How Flutter works

Welcome to the first episode of "How Flutter Works," a six-part series designed to explore what happens to your Dart code after you hand it off to the Flutter framework. This episode takes a high-level look at Flutter's architecture, covering declarative code, multi-platform frameworks, and the role of Dart. This video is perfect for anyone beginning to research Flutter who wants to understand the big picture.

Dive into Flutter's architecture by exploring its three primary trees: Widget, Element, and RenderObject. Discover how widgets provide the declarative API for Flutter developers and see how elements glue widgets to the rendering layer. You'll also learn about the role of render objects in translating widget values into painting calls.

Episode 3 of "How Flutter Works" dives deep into the State class, a critical piece behind every StatefulWidget. Follow the full lifecycle of a State object—from initState, where you initialize resources, to dispose, where you clean up. Along the way, explore important methods including didChangeDependencies, didUpdateWidget, and the all-important build method. By the end of the episode, you'll understand how State objects track, respond to, and manage changes in your Flutter apps—and how the State lifecycle enables efficient UI updates.

This episode also peels back the curtain on how Flutter recurses down the widget tree after a setState call, building out only the parts of your app that need to change. You'll learn why const constructors matter for performance, why setState closures must be synchronous, and how elements (not widgets themselves) manage the actual rebuild process. If you're curious how Flutter keeps apps fast and responsive, or you just want to really understand what happens behind the scenes, this episode is packed with the essential foundations.

Ever wonder how your Flutter app actually renders to the screen? This video dives into RenderObjectWidget—the only type of widget in Flutter that creates something visual. While stateless and stateful widgets help structure your app, it's render object widgets that turn your UI code into real pixels.

You'll learn how Flutter builds the Widget, Element, and RenderObject trees, why many common widgets don't directly render anything, and how Flutter uses RenderObjectWidget to create and update render objects that power your UI.

In Episode 5 of "How Flutter Works," Craig walks through a full day in the life of a RenderObject. Building on the concepts from Episode 4, this video explains the core responsibilities of render objects: layout, painting, hit testing, and accessibility. Craig demystifies how constraints flow down the render tree, how sizes come back up, and how parent render objects set their children's positions. He also breaks down key methods like layout, paint, and describeSemanticsConfiguration, showing how they fit together to keep your UI responsive and accurate.

In Episode 6 of "How Flutter Works," Craig takes us beneath the Dart code to explore the Flutter engine and embedders. This episode explains how Flutter mobile apps rely on native Android and iOS code to launch and operate, how the Flutter engine connects your Dart code to the host platform, and how embedders facilitate communication between the two. Craig also highlights the structure of a newly generated Flutter project, dives into how threads are managed in a Flutter app, and explains the roles of platform channels and the Pigeon package.

You'll also learn why the Flutter engine is written in C++ rather than Dart, how it evolved from a fork of Chrome, and how it uses Skia or Impeller to render each frame. The episode wraps up by looking ahead to Flutter's future architecture improvements, which aim to simplify native interop even further. If you want a clear mental model of how Flutter apps work under the hood, this is the perfect way to connect all the layers together.