Passing data between screens in Flutter - Mini App: Build & Ship

Build: Home and Detail Screens

Build two screens: Home screen with a button to navigate to Detail screen. Pass a message string from Home to Detail and display it there.

Target UI

Home Screen
+---------------------+
|                     |
|  [Go to Detail]     |
|                     |
+---------------------+

Detail Screen
+---------------------+
|                     |
|  Message:           |
|  "Hello from Home"  |
|                     |
+---------------------+

Home screen with a button labeled 'Go to Detail'

On button tap, navigate to Detail screen

Pass a string message 'Hello from Home' to Detail screen

Detail screen displays the passed message in a Text widget

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(
      title: 'Passing Data Demo',
      home: const HomeScreen(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Home Screen')),
      body: Center(
        // TODO: Add ElevatedButton to navigate to DetailScreen with data
      ),
    );
  }
}

class DetailScreen extends StatelessWidget {
  final String message;

  const DetailScreen({super.key, required this.message});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Detail Screen')),
      body: Center(
        // TODO: Display the passed message 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(
      title: 'Passing Data Demo',
      home: const HomeScreen(),
    );
  }
}

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

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Home Screen')),
      body: Center(
        child: ElevatedButton(
          onPressed: () {
            Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) => const DetailScreen(message: 'Hello from Home'),
              ),
            );
          },
          child: const Text('Go to Detail'),
        ),
      ),
    );
  }
}

class DetailScreen extends StatelessWidget {
  final String message;

  const DetailScreen({super.key, required this.message});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(title: const Text('Detail Screen')),
      body: Center(
        child: Text(message, style: const TextStyle(fontSize: 20)),
      ),
    );
  }
}

We created two screens: HomeScreen and DetailScreen. The HomeScreen has a button labeled 'Go to Detail'. When tapped, it uses Navigator.push to open DetailScreen. We pass the string 'Hello from Home' as a parameter to DetailScreen's constructor. The DetailScreen receives this string and shows it inside a Text widget centered on the screen. This way, data is passed simply and clearly between screens.

Final Result

Completed Screen

Home Screen
+---------------------+
|                     |
|  [Go to Detail]     |
|                     |
+---------------------+

Detail Screen
+---------------------+
|                     |
|  Hello from Home    |
|                     |
+---------------------+

User taps 'Go to Detail' button on Home Screen

App navigates to Detail Screen

Detail Screen shows the message 'Hello from Home'

Stretch Goal

Add a back button on Detail screen that returns to Home screen

💡 Hint

Use AppBar's automatically provided back button or Navigator.pop(context) to go back

Practice

1. What is the main purpose of passing data between screens in a Flutter app?

easy

A. To change the app's theme colors dynamically

B. To store data permanently on the device

C. To improve the app's startup speed

D. To share information as the user moves from one screen to another

Solution

1. Step 1: Understand screen navigation

   When users move between screens, apps often need to share information to keep context.

2. Step 2: Identify the role of data passing

   Passing data allows the next screen to display or use information from the previous screen.

3. Final Answer:

   To share information as the user moves from one screen to another -> Option D

4. Quick Check:

   Passing data = share info between screens [OK]

Hint: Passing data shares info between screens during navigation [OK]

Common Mistakes:

• Confusing data passing with theme or style changes
• Thinking data passing stores data permanently
• Assuming data passing speeds up app startup

2. Which Flutter code snippet correctly passes a string "Hello" to a new screen called DetailScreen?

easy

A. Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen("Hello")));

B. Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen));

C. Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen(data: "Hello")));

D. Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen.data("Hello")));

Solution

1. Step 1: Check constructor usage

   Passing data requires calling the screen's constructor with named or positional parameters.

2. Step 2: Verify syntax correctness

   Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen(data: "Hello"))); correctly calls DetailScreen with named parameter data: "Hello" inside the builder.

3. Final Answer:

   Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen(data: "Hello"))); -> Option C

4. Quick Check:

   Correct constructor call = Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen(data: "Hello"))); [OK]

Hint: Use constructor with named params inside MaterialPageRoute builder [OK]

Common Mistakes:

• Omitting parentheses after DetailScreen
• Passing data without parameter name when required
• Using incorrect method calls on DetailScreen

3. Given this code, what will be displayed on the DetailScreen?

class DetailScreen extends StatelessWidget {
  final String message;
  DetailScreen({required this.message});

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(child: Text(message)),
    );
  }
}

// Navigation call:
Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen(message: "Welcome")));

medium

A. An empty screen

B. Text widget showing "Welcome"

C. Error because message is not passed

D. Text widget showing "message" literally

Solution

1. Step 1: Analyze constructor parameter

   DetailScreen requires a String message passed via constructor, which is done correctly with "Welcome".

2. Step 2: Check build method output

   The build method shows a Text widget displaying the message variable, so it will show "Welcome".

3. Final Answer:

   Text widget showing "Welcome" -> Option B

4. Quick Check:

   Passed message = displayed text [OK]

Hint: Passed constructor data shows in Text widget [OK]

Common Mistakes:

• Assuming message is not passed causes error
• Thinking Text shows variable name instead of value
• Ignoring the required keyword in constructor

4. What is wrong with this code snippet for passing data?

Navigator.push(context, MaterialPageRoute(builder: (context) => DetailScreen));

medium

A. DetailScreen is missing parentheses to call its constructor

B. Navigator.push cannot be used for navigation

C. MaterialPageRoute should not have a builder

D. Context is not needed in Navigator.push

Solution

1. Step 1: Check DetailScreen usage

   DetailScreen is a class and must be instantiated by calling its constructor with parentheses.

2. Step 2: Identify missing constructor call

   Without parentheses, DetailScreen is a type, not an instance, causing a syntax error.

3. Final Answer:

   DetailScreen is missing parentheses to call its constructor -> Option A

4. Quick Check:

   Constructor call needs parentheses [OK]

Hint: Always add () to call a widget constructor [OK]

Common Mistakes:

• Forgetting parentheses after widget class name
• Misunderstanding Navigator.push usage
• Thinking context is optional in navigation

5. You want to pass a user ID (integer) from HomeScreen to ProfileScreen and display it. Which approach correctly passes and uses this data?

hard

A. Pass userId via ProfileScreen constructor and display it in a Text widget

B. Store userId in a global variable and access it directly in ProfileScreen

C. Use Navigator.pop to send userId to ProfileScreen

D. Pass userId as a parameter to Navigator.pop

Solution

1. Step 1: Understand data passing direction

   Navigator.push sends data forward to a new screen via constructor parameters.

2. Step 2: Identify correct data usage

   Passing userId via ProfileScreen constructor and displaying it in a Text widget is the proper way.

3. Step 3: Eliminate incorrect options

   Global variables are discouraged; Navigator.pop sends data back, not forward.

4. Final Answer:

   Pass userId via ProfileScreen constructor and display it in a Text widget -> Option A

5. Quick Check:

   Push + constructor = pass data forward [OK]

Hint: Use constructor params to pass data forward between screens [OK]

Common Mistakes:

• Using Navigator.pop to send data forward
• Relying on global variables for passing data
• Passing data as parameters to Navigator.pop