MaterialApp and Scaffold in Flutter - Mini App: Build & Ship

Build: Simple Home Screen

Build a basic Flutter app screen using MaterialApp and Scaffold. The screen should have a top app bar with a title and a centered text message in the body.

Target UI

┌─────────────────────────────┐
│       App Bar Title         │
├─────────────────────────────┤
│                             │
│      Welcome to Flutter!    │
│                             │
└─────────────────────────────┘

Use MaterialApp as the root widget

Use Scaffold inside MaterialApp

Add an AppBar with the title 'App Bar Title'

Center the text 'Welcome to Flutter!' in the body

Starter Code

Flutter

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      // TODO: Add Scaffold here
    );
  }
}

Task 1

Task 2

Task 3

Solution

Flutter

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('App Bar Title'),
        ),
        body: const Center(
          child: Text('Welcome to Flutter!'),
        ),
      ),
    );
  }
}

This Flutter app uses MaterialApp as the root widget to provide material design styling and navigation support. Inside it, Scaffold creates the basic visual layout structure with an AppBar at the top and a Center widget in the body. The AppBar shows the title text, and the Center widget centers the welcome message on the screen. This is a simple and common pattern to start building Flutter apps with material design.

Final Result

Completed Screen

┌─────────────────────────────┐
│       App Bar Title         │
├─────────────────────────────┤
│                             │
│      Welcome to Flutter!    │
│                             │
└─────────────────────────────┘

The app bar stays fixed at the top

The welcome text is centered on the screen

No buttons or gestures yet

Stretch Goal

Add a FloatingActionButton with a '+' icon that shows a SnackBar saying 'Button pressed!' when tapped.

💡 Hint

Use Scaffold's floatingActionButton property and ScaffoldMessenger to show the SnackBar.

Practice

1. What is the main purpose of the MaterialApp widget in a Flutter app?

easy

A. It sets up the app's theme, routes, and basic navigation structure.

B. It creates the main content area of the screen.

C. It displays a button on the screen.

D. It manages the app's database connections.

Solution

1. Step 1: Understand MaterialApp role

   The MaterialApp widget is designed to provide app-wide settings like theme, navigation routes, and localization.

2. Step 2: Differentiate from Scaffold

   Scaffold handles screen layout, not app-wide settings.

3. Final Answer:

   It sets up the app's theme, routes, and basic navigation structure. -> Option A

4. Quick Check:

   MaterialApp = app-wide setup [OK]

Hint: MaterialApp wraps the whole app, setting theme and navigation [OK]

Common Mistakes:

• Confusing Scaffold with MaterialApp
• Thinking MaterialApp creates screen content
• Assuming MaterialApp manages buttons directly

2. Which of the following is the correct way to create a basic Scaffold with an AppBar titled "Home"?

easy

A. Scaffold(appBar: AppBar(title: Text('Home')))

B. Scaffold(AppBar: Text('Home'))

C. Scaffold(appBar: Text('Home'))

D. Scaffold(title: AppBar('Home'))

Solution

1. Step 1: Check Scaffold syntax

   The Scaffold widget requires an appBar property set to an AppBar widget.

2. Step 2: Verify AppBar usage

   AppBar takes a title property which is a Text widget.

3. Final Answer:

   Scaffold(appBar: AppBar(title: Text('Home'))) -> Option A

4. Quick Check:

   Scaffold appBar needs AppBar widget with title [OK]

Hint: Scaffold's appBar expects an AppBar widget with a Text title [OK]

Common Mistakes:

• Using capitalized property names incorrectly
• Passing Text directly to appBar
• Confusing property names like title vs appBar

3. What will be displayed when running this Flutter code?

MaterialApp(
  home: Scaffold(
    appBar: AppBar(title: Text('Welcome')),
    body: Center(child: Text('Hello World')),
  ),
)

medium

A. A blank screen with no content.

B. Only the text 'Hello World' without an app bar.

C. An error because MaterialApp needs a title property.

D. A screen with an app bar titled 'Welcome' and centered text 'Hello World'.

Solution

1. Step 1: Analyze MaterialApp and Scaffold usage

   The MaterialApp wraps the app and sets home to a Scaffold widget.

2. Step 2: Check Scaffold content

   The Scaffold has an AppBar with title 'Welcome' and a body with centered text 'Hello World'.

3. Final Answer:

   A screen with an app bar titled 'Welcome' and centered text 'Hello World'. -> Option D

4. Quick Check:

   MaterialApp + Scaffold shows app bar and body [OK]

Hint: MaterialApp home shows Scaffold with app bar and body [OK]

Common Mistakes:

• Thinking MaterialApp requires a title property
• Ignoring Scaffold's appBar and body
• Assuming no UI appears without explicit runApp

4. Identify the error in this Flutter code snippet:

MaterialApp(
  home: Scaffold(
    appBar: AppBar(title: Text('My App')),
    body: Text('Hello'),
  ),
)

medium

A. Missing a comma after the Scaffold widget.

B. AppBar title must be a String, not a Text widget.

C. The body should be wrapped in a widget like Center or Padding for proper layout.

D. MaterialApp cannot have a Scaffold as home.

Solution

1. Step 1: Check Scaffold body usage

   The body is a Text widget directly, which works but may cause layout issues without padding or centering.

2. Step 2: Identify best practice

   Wrapping Text in Center or Padding improves UI and avoids layout warnings.

3. Final Answer:

   The body should be wrapped in a widget like Center or Padding for proper layout. -> Option C

4. Quick Check:

   Scaffold body needs layout widget for good UI [OK]

Hint: Wrap body Text in Center or Padding to avoid layout issues [OK]

Common Mistakes:

• Thinking AppBar title must be String, not Text
• Believing MaterialApp can't have Scaffold as home
• Ignoring layout best practices for body content

5. You want to create a Flutter app with a blue app bar titled "Dashboard" and a body showing a centered button labeled "Click Me". Which code snippet correctly achieves this?

hard

A. MaterialApp(home: Scaffold(appBar: AppBar(title: 'Dashboard', backgroundColor: Colors.blue), body: Center(child: Button('Click Me'))))

B. MaterialApp(home: Scaffold(appBar: AppBar(title: Text('Dashboard'), backgroundColor: Colors.blue), body: Center(child: ElevatedButton(onPressed: () {}, child: Text('Click Me')))))

C. MaterialApp(home: Scaffold(appBar: AppBar(title: Text('Dashboard'), color: Colors.blue), body: Button('Click Me')))

D. MaterialApp(home: Scaffold(appBar: AppBar(title: Text('Dashboard'), backgroundColor: Colors.blue), body: Center(child: ElevatedButton(child: Text('Click Me')))))

Solution

1. Step 1: Set AppBar title and color correctly

   The AppBar title must be a Text widget and background color set with backgroundColor.

2. Step 2: Use ElevatedButton with onPressed and child

   The button must be an ElevatedButton with an onPressed callback and a Text child.

3. Step 3: Wrap button in Center for alignment

   Center widget ensures the button is centered in the body.

4. Final Answer:

   MaterialApp(home: Scaffold(appBar: AppBar(title: Text('Dashboard'), backgroundColor: Colors.blue), body: Center(child: ElevatedButton(onPressed: () {}, child: Text('Click Me'))))) -> Option B

5. Quick Check:

   AppBar color + ElevatedButton with onPressed + Center [OK]

Hint: Use backgroundColor for AppBar and ElevatedButton with onPressed [OK]

Common Mistakes:

• Using 'color' instead of 'backgroundColor' for AppBar
• Omitting onPressed in ElevatedButton
• Passing title as String instead of Text widget