Hot reload and hot restart in Flutter - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to perform a hot reload in Flutter.

Flutter

void main() {
  runApp(MyApp());
  WidgetsBinding.instance.addPostFrameCallback((_) {
    [1]();
  });
}

Drag options to blanks, or click blank then click option'

AhotRestart

BsetState

CrunApp

DhotReload

Attempts:

3 left

💡 Hint

Common Mistakes

Using hotRestart instead of hotReload causes a full restart.

Calling runApp again reloads the whole app, not just the UI.

Calling runApp() again reloads the UI in Flutter, which is how hot reload is typically triggered programmatically.

2fill in blank

medium

Complete the code to perform a hot restart in Flutter.

Flutter

void main() {
  runApp(MyApp());
  [1]();
}

Drag options to blanks, or click blank then click option'

AhotReload

BhotRestart

CsetState

Drebuild

Attempts:

3 left

💡 Hint

Common Mistakes

Using hotReload instead of hotRestart keeps the app state.

Calling setState only rebuilds widgets, not the whole app.

The method hotRestart() restarts the Flutter app fully, clearing all state.

3fill in blank

hard

Fix the error in the code to trigger hot reload correctly.

Flutter

void main() {
  runApp(MyApp());
  WidgetsBinding.instance.[1](() {
    print('Hot reload triggered');
  });
}

Drag options to blanks, or click blank then click option'

AaddReloadCallback

BaddListener

CaddObserver

DaddPostFrameCallback

Attempts:

3 left

💡 Hint

Common Mistakes

Using addListener or addObserver causes errors as they don't exist here.

addReloadCallback is not a Flutter method.

addPostFrameCallback schedules a callback after the current frame, suitable for hot reload triggers.

4fill in blank

hard

Fill both blanks to create a button that triggers hot reload when pressed.

Flutter

ElevatedButton(
  onPressed: () {
    [1]();
  },
  child: Text('[2]'),
)

Drag options to blanks, or click blank then click option'

AhotReload

BhotRestart

CReload UI

DRestart App

Attempts:

3 left

💡 Hint

Common Mistakes

Using hotRestart() here restarts the whole app, not just UI.

Button text should match the action for clarity.

The button calls hotReload() and shows text 'Reload UI' to indicate hot reload action.

5fill in blank

hard

Fill all three blanks to create a button that triggers hot restart and shows correct label.

Flutter

ElevatedButton(
  onPressed: () {
    [1]();
  },
  child: Text('[2]'),
  style: ButtonStyle(
    backgroundColor: MaterialStateProperty.all<Color>([3]),
  ),
)

Drag options to blanks, or click blank then click option'

AhotReload

BhotRestart

CRestart App

DColors.red

Attempts:

3 left

💡 Hint

Common Mistakes

Using hotReload() instead of hotRestart() changes behavior.

Incorrect color value causes UI errors.

The button calls hotRestart(), shows 'Restart App' label, and has a red background color.

Practice

1. What is the main difference between hot reload and hot restart in Flutter?

easy

A. Both hot reload and hot restart reset app state.

B. Hot reload resets app state; hot restart updates code without resetting state.

C. Both hot reload and hot restart keep app state unchanged.

D. Hot reload updates code and keeps app state; hot restart resets app state.

Solution

1. Step 1: Understand hot reload behavior

   Hot reload updates the code quickly and keeps the current app state intact.

2. Step 2: Understand hot restart behavior

   Hot restart restarts the whole app and resets the app state to initial.

3. Final Answer:

   Hot reload updates code and keeps app state; hot restart resets app state. -> Option D

4. Quick Check:

   Hot reload = keeps state, Hot restart = resets state [OK]

Hint: Hot reload keeps state; hot restart resets state [OK]

Common Mistakes:

• Confusing which method resets app state
• Thinking hot reload restarts the app
• Assuming both behave the same

2. Which of the following is the correct Flutter command to perform a hot reload?

easy

A. flutter hot-reload

B. flutter run --restart

C. Press 'r' in the terminal running flutter

D. Press 'R' in the terminal running flutter

Solution

1. Step 1: Identify hot reload command

   Pressing lowercase 'r' in the terminal triggers hot reload during flutter run.

2. Step 2: Differentiate from hot restart command

   Pressing uppercase 'R' triggers hot restart, not hot reload.

3. Final Answer:

   Press 'r' in the terminal running flutter -> Option C

4. Quick Check:

   Lowercase 'r' = hot reload [OK]

Hint: Press lowercase 'r' for hot reload in terminal [OK]

Common Mistakes:

• Pressing uppercase 'R' for hot reload
• Using wrong flutter CLI commands
• Assuming hot reload needs special flags

3. Consider this Flutter app code snippet:

int counter = 0;

void increment() {
  counter++;
}

// After hot reload, what is the value of counter if increment() was called 3 times before reload?

medium

A. 0

B. 3

C. 1

D. Error: counter reset

Solution

1. Step 1: Understand hot reload effect on state

   Hot reload updates code but keeps current app state, so counter value stays as before.

2. Step 2: Apply increment calls before reload

   Counter was incremented 3 times, so its value is 3 after hot reload.

3. Final Answer:

   3 -> Option B

4. Quick Check:

   Hot reload keeps state, so counter = 3 [OK]

Hint: Hot reload keeps variable values unchanged [OK]

Common Mistakes:

• Assuming counter resets to 0
• Confusing hot reload with hot restart
• Thinking hot reload causes errors

4. You made a change to your Flutter app's main() function but after hot reload, the change does not appear. What is the likely cause?

medium

A. Hot reload does not update main() function; hot restart is needed.

B. Hot reload always updates main(), so this is a bug.

C. You need to stop and restart the app manually.

D. Hot reload only works on Android, not iOS.

Solution

1. Step 1: Know hot reload limitations

   Hot reload does not re-run main() or reset app state, so changes in main() won't appear.

2. Step 2: Use hot restart for main() changes

   Hot restart restarts the app and runs main() again, applying changes.

3. Final Answer:

   Hot reload does not update main() function; hot restart is needed. -> Option A

4. Quick Check:

   Main() changes require hot restart [OK]

Hint: Main() changes need hot restart, not hot reload [OK]

Common Mistakes:

• Expecting hot reload to update main()
• Thinking hot reload works differently on platforms
• Restarting app manually instead of hot restart

5. You have a Flutter app with a complex state that takes time to initialize. You want to quickly test UI changes without losing the current state. Which approach is best?

hard

A. Use hot reload to update UI and keep state.

B. Use hot restart to reload app and reset state.

C. Stop and restart the app manually.

D. Modify main() and then hot reload.

Solution

1. Step 1: Consider app state complexity

   Since state is complex and slow to initialize, preserving it saves time.

2. Step 2: Choose method that keeps state

   Hot reload updates UI code quickly without resetting state, ideal for this case.

3. Step 3: Avoid hot restart or manual restart

   These reset state and cause delay due to reinitialization.

4. Final Answer:

   Use hot reload to update UI and keep state. -> Option A

5. Quick Check:

   Keep state with hot reload for fast UI testing [OK]

Hint: Use hot reload to keep state and update UI fast [OK]

Common Mistakes:

• Using hot restart and losing state
• Restarting app manually unnecessarily
• Trying to hot reload after main() changes