What are widgets in Flutter?

Question

Accepted Answer

In Flutter, **everything is a widget** — UI elements (buttons, text, images), layout structures (rows, columns, padding), and even the app itself are all widgets. Widgets are the immutable building blocks that compose to form the entire user interface.

## Everything is a widget

```text
Widgets describe the UI. EVERYTHING is a widget:
  → visible elements: Text, Image, Icon, Button, etc.
  → layout: Row, Column, Container, Padding, Center, Stack, etc.
  → structure: Scaffold (page structure), AppBar, etc.
  → even the app itself (MaterialApp) and abstract things (Padding, Theme)
→ You build UI by COMPOSING widgets into a tree (widgets contain other widgets).
```

## Composing widgets into a tree

```dart
// build a UI by NESTING widgets (composition)
Scaffold(                       // page structure
  appBar: AppBar(title: Text('Home')),   // app bar with text
  body: Center(                 // centers its child
    child: Column(              // vertical layout
      children: [
        Text('Hello'),          // text widget
        ElevatedButton(         // a button
          onPressed: () {},
          child: Text('Click'),
        ),
      ],
    ),
  ),
)
// → a WIDGET TREE: Scaffold > Center > Column > [Text, Button]
```

Widgets nest to form a **widget tree** — composition is the core pattern (combine simple widgets into complex UIs).

## Widgets are immutable; configuration

```text
→ Widgets are IMMUTABLE descriptions of the UI (configuration, not the actual rendered
  objects) — Flutter rebuilds them efficiently when state changes
→ build() methods return widget trees describing what the UI should look like
→ Flutter handles efficiently turning widgets into rendered pixels
```

## Why it matters

Understanding widgets is fundamental to Flutter because **everything in Flutter is a widget** — the entire UI is built from them — so grasping the widget model is essential, foundational knowledge for any Flutter development.

The core concept — that visible elements (text, buttons, images), layout structures (rows, columns, padding), page structure, and even the app itself are **all widgets** — is the defining characteristic of how Flutter works, and understanding it is the starting point for building any Flutter UI.

Understanding that UIs are built by **composing widgets into a tree** (nesting widgets, combining simple ones into complex interfaces) is the fundamental pattern of Flutter development — composition over inheritance, building complex UIs from simple, reusable building blocks.

Understanding that **widgets are immutable descriptions** of the UI (configuration rather than the actual rendered objects, with Flutter efficiently rebuilding them when state changes) is important for understanding how Flutter's declarative UI model works — you describe what the UI should look like, and Flutter handles rendering efficiently.

This widget-and-composition model underlies everything in Flutter: layouts, styling, state management, and structure all work through widgets.

Since the widget is the atomic unit of Flutter (everything is a widget, UIs are widget trees built by composition) and understanding this model is the absolute foundation for building Flutter UIs, understanding widgets — that everything is a widget, composition into trees, and their immutable declarative nature — is essential, foundational Flutter knowledge, the core concept that every aspect of Flutter development builds upon and the first thing to understand when learning Flutter.