Passing data between screens in Flutter - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ ui_behavior

intermediate

Passing data with Navigator.push

What will be displayed on the second screen after navigating from the first screen with the given code?

Flutter

class FirstScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () {
        Navigator.push(
          context,
          MaterialPageRoute(
            builder: (context) => SecondScreen(data: 'Hello'),
          ),
        );
      },
      child: Text('Go'),
    );
  }
}

class SecondScreen extends StatelessWidget {
  final String data;
  SecondScreen({required this.data});

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

A The second screen shows a blank screen

B The app crashes with a runtime error

C The second screen shows a centered text: Hello

D The second screen shows the text: Go

💡 Hint

Check how the data is passed through the constructor and displayed in the Text widget.

The FirstScreen passes the string 'Hello' to SecondScreen via its constructor. SecondScreen displays this string in a centered Text widget.

🧠 Conceptual

intermediate

Understanding Navigator.pop with data

What value will be received in the first screen after popping the second screen with Navigator.pop(context, 42)?

Flutter

class FirstScreen extends StatefulWidget {
  @override
  State<FirstScreen> createState() => _FirstScreenState();
}

class _FirstScreenState extends State<FirstScreen> {
  int? result;

  void _navigate() async {
    final data = await Navigator.push<int>(
      context,
      MaterialPageRoute(builder: (context) => SecondScreen()),
    );
    setState(() {
      result = data;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        ElevatedButton(onPressed: _navigate, child: Text('Go')),
        if (result != null) Text('Result: $result'),
      ],
    );
  }
}

class SecondScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () {
        Navigator.pop(context, 42);
      },
      child: Text('Return 42'),
    );
  }
}

A The first screen shows the text: Result: 42

B The first screen shows no text

C The app crashes with a type error

D The first screen shows the text: Result: null

💡 Hint

Navigator.pop can send data back to the previous screen using the second argument.

Navigator.pop(context, 42) sends the integer 42 back to the first screen, which receives it via await and updates the UI.

❓ lifecycle

advanced

State retention when passing data between screens

Given the code below, what will be the value of counter on the first screen after returning from the second screen?

Flutter

class FirstScreen extends StatefulWidget {
  @override
  State<FirstScreen> createState() => _FirstScreenState();
}

class _FirstScreenState extends State<FirstScreen> {
  int counter = 0;

  void _navigate() async {
    final increment = await Navigator.push<int>(
      context,
      MaterialPageRoute(builder: (context) => SecondScreen()),
    );
    if (increment != null) {
      setState(() {
        counter += increment;
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text('Counter: $counter'),
        ElevatedButton(onPressed: _navigate, child: Text('Go')),
      ],
    );
  }
}

class SecondScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () {
        Navigator.pop(context, 5);
      },
      child: Text('Add 5'),
    );
  }
}

A The first screen shows: Counter: null

B The first screen shows: Counter: 0

C The app crashes with a runtime error

D The first screen shows: Counter: 5

💡 Hint

The first screen updates its state with the value returned from the second screen.

The second screen returns 5 via Navigator.pop. The first screen adds this to counter and updates the UI.

📝 Syntax

advanced

Correct way to pass multiple data items between screens

Which option correctly passes two strings, name and email, from FirstScreen to SecondScreen?

Flutter

class SecondScreen extends StatelessWidget {
  final String name;
  final String email;
  SecondScreen({required this.name, required this.email});

  @override
  Widget build(BuildContext context) {
    return Text('$name - $email');
  }
}

// In FirstScreen, which code is correct to navigate?

A Navigator.push(context, MaterialPageRoute(builder: (context) => SecondScreen('Alice', '[e-mail]')));

B Navigator.push(context, MaterialPageRoute(builder: (context) => SecondScreen(name: 'Alice', email: '[e-mail]')));

C Navigator.push(context, MaterialPageRoute(builder: (context) => SecondScreen(name: 'Alice')));

D Navigator.push(context, MaterialPageRoute(builder: (context) => SecondScreen(email: '[e-mail]')));

💡 Hint

Check the constructor parameters and how named arguments are passed in Dart.

SecondScreen requires named parameters name and email. Option B correctly passes both named arguments.

🔧 Debug

expert

Why does data not update after returning from second screen?

Given the code below, why does the first screen not show the updated data after returning from the second screen?

Flutter

class FirstScreen extends StatefulWidget {
  @override
  State<FirstScreen> createState() => _FirstScreenState();
}

class _FirstScreenState extends State<FirstScreen> {
  String data = 'Old';

  void _navigate() {
    Navigator.push(
      context,
      MaterialPageRoute(builder: (context) => SecondScreen()),
    ).then((value) {
      data = value ?? data;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        Text(data),
        ElevatedButton(onPressed: _navigate, child: Text('Go')),
      ],
    );
  }
}

class SecondScreen extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return ElevatedButton(
      onPressed: () {
        Navigator.pop(context, 'New');
      },
      child: Text('Return New'),
    );
  }
}

A Because setState is not called after updating data, so UI does not refresh

B Because Navigator.pop does not send data back correctly

C Because the initial value of data is final and cannot be changed

D Because the Text widget cannot display variables

💡 Hint

Remember how Flutter updates the UI when state changes.

The data variable is updated but setState is not called, so Flutter does not rebuild the widget to show the new data.

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