Bottom navigation bar in Flutter - UI Render Trace

Component - Bottom navigation bar

A Bottom Navigation Bar is a horizontal bar at the bottom of the screen that lets users switch between main sections of an app quickly. It usually shows icons and labels for each section.

Widget Tree

Scaffold
├── AppBar
├── body: Center
│   └── Text
└── bottomNavigationBar: BottomNavigationBar
    ├── BottomNavigationBarItem (Home)
    ├── BottomNavigationBarItem (Search)
    └── BottomNavigationBarItem (Profile)

The Scaffold widget provides the basic layout with an AppBar at the top, a centered text in the body, and a BottomNavigationBar at the bottom. The BottomNavigationBar contains three items: Home, Search, and Profile, each represented by an icon and label.

Render Trace - 3 Steps

Step 1: Scaffold

Step 2: body: Center

Step 3: bottomNavigationBar: BottomNavigationBar

State Change - Re-render

Trigger:User taps the 'Search' tab icon in the BottomNavigationBar.

Before

currentIndex = 0 (Home tab selected), body text shows 'Selected tab: Home'.

→

After

currentIndex = 1 (Search tab selected), body text updates to 'Selected tab: Search'.

Re-renders:The Scaffold's body and BottomNavigationBar re-render to reflect the new selected tab.

UI Quiz - 3 Questions

What happens when the user taps a different tab in the BottomNavigationBar?

A The selected tab changes and the body updates to show the new tab name.

B The app closes automatically.

C Nothing changes on the screen.

D The app shows an error message.

Key Insight

Using a BottomNavigationBar helps users switch between main app sections easily. It should be simple, visible, and highlight the current selection clearly. Scaffold's bottomNavigationBar property is the standard way to add it in Flutter.