Top 67 Flutter Interview Questions And Answers

Question 1

When to use _main Axis Alignment_ and _cross Axis Alignment_?

Accepted Answer

**For Row:**  
`mainAxisAlignment` = Horizontal Axis   
`crossAxisAlignment` = Vertical Axis

![enter image description here](https://i.stack.imgur.com/aypHr.png)

**For Column:**
  
`mainAxisAlignment` = Vertical Axis      
`crossAxisAlignment` = Horizontal Axis

![enter image description here](https://i.stack.imgur.com/eseWF.png)

[Image source](https://flutter.dev/docs/development/ui/layout#aligning-widgets)

Question 2

What is Flutter?

Accepted Answer

**Flutter** is an open-source UI toolkit from *Google* for crafting beautiful, natively compiled applications for desktop, web, and mobile from a single codebase. Flutter apps are built using the *Dart* programming language.

Question 3

What is the difference between `main()` and `runApp()` functions in Flutter?

Accepted Answer

- `main ()` function came from *Java*-like languages so it's where all program started, without it, you can't write any program on Flutter even without UI.
- `runApp()` function should return *Widget* that would be attached to the screen as a root of the *Widget Tree* that will be rendered.

Question 4

What are the different _build modes_ in Flutter?

Accepted Answer

- The Flutter tooling supports three modes when compiling your app, and a headless mode for testing. 
- You choose a compilation mode depending on where you are in the development cycle.
- The modes are:
	- Debug
	- Profile
	- Release

Question 5

When should you use `WidgetsBindingObserver`?

Accepted Answer

WidgetsBindingObserver should be used when we want to listen to the `AppLifecycleState` and call stop/start on our services.

Question 6

What is an _App state_?

Accepted Answer

- State that is not *ephemeral*, that you want to share across many parts of your app, and that you want to keep between user sessions, is what we call **application state** (sometimes also called *shared state*).
- Examples of application state:
	-   User preferences
	-   Login info
	-   Notifications in a social networking app
	-   The shopping cart in an e-commerce app
	-   Read/unread state of articles in a news app

Question 7

Does Flutter work like a browser? How is it different from a _WebView_ based application?

Accepted Answer

To answer this question simply: **Code you write for a WebView or an app that runs similarly has to go through multiple layers to finally get executed.** In essence, Flutter leapfrogs that by **compiling down to native ARM** code to execute on both platforms. “Hybrid” apps are slow, sluggish and look different from the platform they run on. Flutter apps run much, much faster than their hybrid counterparts. Also, it’s much easier to access native components and sensors using plugins rather than using WebViews which can’t take full use of their platform.

Question 8

How many types of widgets are there in Flutter?

Accepted Answer

There are two types of widgets:
1.  **StatelessWidget** : A widget that does not require mutable state.
2.  **StatefulWidget**: A widget that has mutable state.

Question 9

What is _Dart_ and why does Flutter use it?

Accepted Answer

**Dart** is an *object-oriented*, *garbage-collected* programming language that you use to develop Flutter apps.
It was also created by Google, but is open-source, and has community inside and outside Google.
Dart was chosen as the language of **Flutter** for the following reason: 
- Dart is **AOT** (Ahead Of Time) compiled to fast, predictable, native code, which allows almost all of Flutter to be written in Dart. This not only makes Flutter fast, virtually everything (including all the widgets) can be customized.
- Dart can also be **JIT** (Just In Time) compiled for exceptionally fast development cycles and game-changing workflow (including Flutter’s popular sub-second stateful hot reload).
- Dart allows Flutter to avoid the need for a separate declarative layout language like *JSX* or *XML*, or separate visual interface builders, because Dart’s declarative, programmatic layout is easy to read and visualize. And with all the layout in one language and in one place, it is easy for Flutter to provide advanced tooling that makes layout a snap.

Question 10

What is the `pubspec.yaml` file and what does it do?

Accepted Answer

- The `pubspec.yaml` file allows you to define the packages your app relies on, declare your assets like images, audio, video, etc. 
- It allows you to set constraints for your app. 
- For Android developers, this is roughly similar to a `build.gradle` file.

Top 67 Flutter Interview Questions

When to use main Axis Alignment and cross Axis Alignment?

What is Flutter?

What is the difference between Expanded and Flexible widgets?

What are the different build modes in Flutter?

What is Dart and why does Flutter use it?

How many types of widgets are there in Flutter?

What is an App state?

What is the difference between main() and runApp() functions in Flutter?

How is Flutter different from a WebView based application?

When should you use WidgetsBindingObserver?

What is a widget ? Mention its importance in Flutter.

Does Flutter work like a browser? How is it different from a WebView based application?

What is Fat Arrow Notation in Dart and when do you use it?

What is the pubspec.yaml file and what does it do?

How do you check if an async void method is completed in Dart?

Differentiate between required and optional parameters in Dart

Where are the layout files? Why doesn’t Flutter have layout files?

Name some cons of using Flutter?

What are some pros of Flutter?

Why is the build() method on State and not Stateful Widget?

How is whenCompleted() different from then() in Future?

How to declare async function as a variable in Dart?

What are keys in Flutter and when to use it?

Differentiate StatelessWidget and StatefulWidget?

When do we use double.INFINITY?

What is debug mode and when do you use it?

How is InheritedWidget different from Provider?

Differentiate between Hot Restart and Hot Reload?

Explain Navigator Widget and its push/pop functions in Flutter?

What is ScopedModel / BLoC Pattern?

What is the difference between Scaffold and Container in Flutter?

What are Null-aware operators?

Differentiate between named parameters and positional parameters in Dart?

What is release mode and when do you use it?

What are Streams in Flutter/Dart?

What is profile mode and when do you use it?

Why do we pass functions to widgets?

What are packages and plugins in Flutter?

Do you know what Ephemeral state means?

Explain the different types of Streams?

What are the similarities and differences of Future and Stream?

What are some pros and cons of Scoped Model vs BLoC and vice versa?

Why should you use kReleaseMode instead of assert?

What's the difference between async and async* in Dart?

How to compare two dates that are constructed differently in Dart?

What does non-nullable by default mean in Dart?

What is the difference between React Native and Flutter in-depth?

How do you convert a List into a Map in Dart?

Explain async, await in Flutter/Dart?

What is the difference between double.INFINITY and MediaQuery?

What is Future in Flutter/Dart?

What is the purpose of SafeArea in Flutter?

How does Dart AOT work?

What are Global Keys?

Why is exit(0) not preferred for closing an app?

What does a class with a method named ._() mean in Dart/Flutter?

What is a MediaQuery in Flutter and when do we use it?

When would you use App state or Ephemeral state over another?

What is a difference between these operators ?? and ?.

How is AnimationController different from Timer?

What are StatefulWidget and State Separate Classes?

What is the difference between debug mode and profile mode?

List some approaches for State Management in Flutter

Explain Stateful Widget Lifecycle in details

How would you execute code only in debug mode?

How to get difference of lists in Flutter/Dart?

How to duplicate repeating items inside a Dart list?

What is the difference between `main()` and `runApp()` functions in Flutter?

When should you use `WidgetsBindingObserver`?

What is the `pubspec.yaml` file and what does it do?

How do you check if an `async void` method is completed in Dart?

Why is the `build()` method on State and not Stateful Widget?

How is `whenCompleted()` different from `then()` in Future?

Differentiate `StatelessWidget` and `StatefulWidget`?

When do we use `double.INFINITY`?

How is `InheritedWidget` different from `Provider`?

What is the difference between `Scaffold` and `Container` in Flutter?

What are `Null-aware` operators?

Why should you use `kReleaseMode` instead of `assert`?

What's the difference between `async` and `async*` in Dart?

How do you convert a `List` into a `Map` in Dart?

Explain `async`, `await` in Flutter/Dart?

What is the difference between `double.INFINITY` and `MediaQuery`?

What is the purpose of `SafeArea` in Flutter?

How does Dart `AOT` work?

Why is `exit(0)` not preferred for closing an app?

What does a class with a method named `._()` mean in Dart/Flutter?

What is a `MediaQuery` in Flutter and when do we use it?

What is a difference between these operators `??` and `?.`

How is `AnimationController` different from `Timer`?

What are `StatefulWidget` and `State Separate` Classes?