Hot reload and hot restart in Flutter - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is hot reload in Flutter?

Hot reload updates the running app's code instantly without restarting the whole app. It preserves the app state and shows UI changes quickly.

beginner

What does hot restart do in Flutter?

Hot restart restarts the app completely, losing the current state but applying all code changes from the start.

intermediate

When should you use hot reload instead of hot restart?

Use hot reload to quickly see UI or logic changes without losing app state, like changing colors or layouts.

intermediate

When is hot restart necessary?

Hot restart is needed when you change app initialization code, global variables, or dependencies that hot reload can't update.

beginner

How do hot reload and hot restart improve Flutter development?

They speed up development by reducing wait times. Hot reload lets you see changes instantly, and hot restart resets the app quickly without a full rebuild.

What happens to the app state during a hot reload?

A The app state is reset

B The app state is preserved

C The app closes and restarts

D The app crashes

Hot reload updates code without losing the current app state.

Which action restarts the app and loses the current state?

A Hot reload

B Debug mode

C Hot restart

D Build APK

Hot restart restarts the app fully and resets the state.

Which change requires a hot restart instead of hot reload?

A Changing button color

B Changing layout padding

C Changing text in a widget

D Changing app initialization code

App initialization code changes need a full restart to take effect.

How does hot reload help developers?

A By instantly showing UI changes without losing state

B By closing the app

C By rebuilding the entire app

D By deleting app data

Hot reload quickly updates UI and logic while keeping app state.

Which Flutter feature speeds up development by reducing wait times?

A Hot reload and hot restart

B Full rebuild

C Manual code refresh

D App store deployment

Hot reload and hot restart let developers see changes quickly without full rebuilds.

Explain the difference between hot reload and hot restart in Flutter.

Think about what happens to the app state and how fast changes appear.

Describe scenarios when you would use hot reload versus hot restart during Flutter app development.

Consider what kind of code changes affect app state or initialization.

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