Build owner

Learn how BuildOwner drives the build process.

Build owner

BuildOwner is the object that manages the build process. When a widget is marked dirty, scheduleBuild schedules a build for the next frame. BuildOwner tracks which elements need to be rebuilt.

final owner = BuildOwner();
owner.scheduleBuildFor(element);
owner.buildScope(element);

Dirty element

When setState is called, an element is flagged as dirty. BuildOwner collects dirty elements and rebuilds them inside buildScope. This is Flutter's efficient update model.

Exercise BuildOwner instance

In main, create a BuildOwner instance and print its runtimeType.

Show example solution

import 'package:flutter/widgets.dart';

void main() {
  final owner = BuildOwner();
  print(owner.runtimeType);
}

Test yourself

What does scheduleBuild do?
- Creates a RenderObject
- Schedules a dirty element to be built in the next frame
- Makes an HTTP call
- Deletes the element
Show answer

Schedules a dirty element to be built in the next frame — scheduleBuild enqueues a dirty-marked element to be built in the next frame by BuildOwner; it does not build immediately.

buildScope call

owner.____(element);

Show answer

owner.buildScope(element);

BuildOwner matches

BuildOwner

Build manager
scheduleBuild

Schedules build
dirty

Needs rebuild
buildScope

Build scope

Next lesson: Summary - Flutter internals

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