When Hot Reload is invoked, the host machine looks at the edited code since the last compilation. The following libraries are recompiled.
Any libraries with changed code
The application’s main library
The libraries from the main library leading to affected libraries
The source code from those libraries is compiled into kernel files and sent to the mobile device’s Dart VM. The Dart VM re-loads all libraries from the new kernel file. So far no code is re-executed. The hot reload mechanism then causes the Flutter framework to trigger a rebuild/re-layout/repaint of all existing widgets and render objects.