Reactive User Interfaces

Flutter's UI is "reactive." This means the UI changes automatically when the app's data changes. Imagine a music app showing a play button. When you press play, the app's state changes and the button changes to a pause button. Flutter handles these changes smoothly.

This reactive nature comes from the "React" framework by Facebook. In older frameworks, changing the UI was harder. Developers had to manually update the UI for each data change. This was complex and error-prone. Flutter makes this easier.

How Flutter Manages UI

In Flutter, everything on the screen is a widget. Widgets are like building blocks. You use them to describe what the UI looks like. Flutter then takes care of showing it on the screen.

Widgets in Flutter are immutable. This means once you create a widget, you can't change it. If you want a different widget, you create a new one. This may sound inefficient, but Dart, the language used in Flutter, handles this very well.

Flutter separates the creation of UI from its underlying state. This separation is key to Flutter's reactive nature. You define UI as a function of the state:

UI = f(state)

Whenever the state changes, Flutter calls the build() method of the widget. This method describes how the UI looks based on the current state. Since this method can be called often, it's designed to be fast and free of side effects.

Key Takeaways

• Flutter uses reactive user interfaces, meaning the UI updates automatically as the app's state changes.