Flutter Interview Questions

​Flutter is a freeware UI software development kit(SDK) or toolkit built by Google for developing web, desktop, and mobile applications through a single codebase. Flutter applications utilize Dart programming language to create applications. Flutter’s first alpha version was released in 2017. Flutter is optimized for 2D mobile applications that execute on both iOS and Android platforms.

Following are the main elements of Flutter:

• Flutter engine
• Dart platform
• Design-specific widgets
• Foundation Library

Dart is a general-purpose and object-oriented programming language with C-language syntax. It is freeware and was built by Google in 2011. Dart programming intends to create the frontend user interface for mobile and web apps. 

Following are the primary advantages of Flutter:

• Flexible and Expressive UI: Flutter offers personalizable layered architecture that assists in expressive UI, flexible design, and rapid rendering.
• Faster Deployment: It provides fast development due to its “hot reload” feature. We can maintain the state on the sub-second reload times.
• Native Performance: Dart compilers have a crucial role in compiling our flutter code because the code can be compiled into natural ARM machine code through the native compilers of Dart. It has natural performance on both iOS and Android.
• Flutter offers you accessibility and internationalization for a wide variety of users globally.

A Flutter application is defined as a tree of widgets. Every time we try to code for developing anything in Flutter, it will be in the widget. Widgets explain how our application must look like with its present state and configuration. When we make any change in the code, the widget reconstructs its description by computing the difference of current and previous widgets to evaluate the minimum changes to render the UI of the app.

We can access the screen size and other properties like aspect ratio, pixel density, etc. through MediaQuery.

Example:MediaQuery.of(Context).size,width

Dart does not endorse multiple inheritances. Therefore for implementing multiple inheritances in Flutter. We require mixins. Mixins offer a way for providing a way for writing the reusable class code in multiple class hierarchies.

No, Flutter is the SDK.

Tree Shaking is the optimization technique for removing the unutilized module in the bundle in the build process. It is also the code elimination technique used for optimizing our application.

It is the configuration file of the project that utilizes a lot while working with the Flutter project. It enables us to monitor how our application operates. It also enables us to configure the constraints for the application. This file includes:

• Project Assets
• Project Dependencies
• Project common settings like project version, description, and name.

A package is defined as a set of similar types of interfaces, sub-packages, and classes. The plug-ins and packages allow us to develop the app without developing everything from the packages. In the Flutter, it enables us to import the latest widgets or functionalities into the application. The plugins and packages have a small difference. Basically, packages are the latest elements or code built-in dart programming language, while plugins enable more functionality on the device through native code.

When we build the Flutter application the first time, it will take more time. It is because Flutter developed the device-specific IPA or APK file. So, the Xcode and Gradle are used for building the file, taking more time.

Tween Animation is a short form of in-betweening. In Tween Animation, we must define the starting and endpoint of the automation. It indicates that the animation starts with the starting value, after that, it goes through a series of intermediary values, and lastly arrives at the end value. It also offers the curve and timeline that defines the speed and time of the variation.

Today, various companies utilize Flutter to build applications. Following are the popular applications developed on Flutter:

1. Google Ads
2. Alibaba
3. Reflectly
4. Coach Yourself
5. Birch Finance
6. Watermaniac
7. Tencent

The latest version of Flutter is Flutter - v1.20.4 released on 15th September 2020.

The Famous and Most used database packages in the Flutter are:

• Firebase Database: It allows us to manipulate and access cloud databases.
• sqflite database: It enables us to manipulate and access the SQLite database.

• The main() function is used to start the program. Without the main() function, we cannot start any program on the Flutter.
• The runApp() is used to return widgets attached to the screen as the root of the widget tree and will be imparted on the screen.

The Flutter SDK supports three modes while compiling the application. We can select these compilation modes by relying on where we are in the development lifecycle. Following are the mode names:

• Profile
• Debug
• Release

Profile Mode is used for measuring the performance of the applications. In the Profile Mode, some debugging capability is preserved for profiling the performance of our app. This mode is deactivated on the simulator and emulator as they are not delegates of the real performance. For profiling the mode, we use the following

command:

flutter run --profile

In Flutter, BuildContext is the part of the widgets in the element tree such that every widget has its BuildContext. We primarily use it for getting a reference to another theme or widget. For instance, if we have the material design element, it is needed to reference it to the scaffold. We can retrieve it through the Scaffold. of(context) method.

Flutter is known to vigorously depend on gadgets (like how React utilizes parts). Each gadget is utilized to execute a form() work and these units of synthesis make up the whole UI. In this way, any arrangement of Flutter specialized inquiries questions that do exclude gadget-related requests is generally most likely insufficient.

Yes, Flutter is a free and open-source UI toolkit by Google to develop desktop, web and mobile applications with one codebase only.

When you build the Flutter app the first time, it will take a longer time. It is because Flutter built the device-specific APK or IPA file. Thus, the Gradle and Xcode are used to build the file, taking a long time.

There are two types of widgets:

• StatelessWidget : A widget that does not require mutable state.
• StatefulWidget: A widget that has mutable state.

Indeed, Flutter is a free and open-source UI programming improvement unit from Google that permits engineers to construct cross-stage portable applications effortlessly.

Flutter uses only the canvas of the native platform and draws the UI and all the components from scratch. All the UI elements look the same as native ones. This mainly reduces the burden of time for converting through some language to the native one and speeds up the UI rendering time. As a result, the UI performance is remarkably high

To build a flexible space, the Spacer class is used. With the flex container, this space maintains the distance between both widgets. The constructor of the Spacer uses flex to determine the space.

A VM (Virtual Machine) runs flutter code during debug mode to provide a hot stateful reload functionality. A “debug” banner will appear in the top right corner when you start the program in debug mode. It serves as a reminder that efficiency is not a defining feature of a finished app.

​Navigation and routing are key principles in all mobile apps, letting users switch between pages. We all know that every mobile application has multiple screens for displaying various types of information. An app, for example, could have a screen with a variety of products. When the user taps on that product, detailed information is displayed immediately.

GlobalKeys allow widgets to move parents without losing state anywhere in your app, or they can be used to acquire information about the other widget in a specific region of the widget tree. You’d use a GlobalKey in the first instance if you wanted to demonstrate the same widget on two distinct screens while keeping them all in the same state.

The dart2js compiler generates the JavaScript bundle when compiling a Flutter web application. A release build has the most significant optimization standard, which includes tree-shaking your code. Tree shaking completely removes dead code by including only code executed. This means you don’t have to be concerned with the state of your app’s included archives because unused classes or functions are removed from the executable JavaScript bundle.

There are several ways to optimize the performance of a Flutter app, including:

• Using efficient algorithms and data structures
• Minimizing the number of widgets in the widget tree
• Using lazy loading and pagination
• Profiling the app using the Flutter DevTools to identify performance bottlenecks
• Using caching and offline support where appropriate

A plugin is a piece of software that adds capabilities to your app. For e.g. you might want your mobile app to interact with the camera on your device. Plugins are an important part of the Flutter ecosystem.

In the broadest possible sense, the state of an app is everything that exists in memory when the app is running.

The biggest problem is the lack of comparable library support.

A widget is either stateful or stateless. If a widget can change—when a user interacts with it, for example—it's stateful. A stateless widget never changes. Icon, IconButton, and Text are examples of stateless widgets.

A Stream provides a way to receive a sequence of events. Each event is either a data event, also called an element of the stream, or an error event, which is a notification that something has failed. When a stream has emitted all its event, a single "done" event will notify the listener that the end has been reached.

Flutter widget inspector is a powerful tool for visualizing and exploring Flutter widget trees. The Flutter framework uses widgets as the core building block for anything from controls (such as text, buttons, and toggles) to layouts (such as centering, padding, rows, and columns).

When you await an asynchronous function, the execution of the code within the caller suspends while the async operation is executed. When the operation is completed, the value of what was awaited is contained within a Future object.

The biggest difference between React Native and Flutter is that Flutter has plugins developed by the Google team, like geolocation and mapping.

In Flutter, a container class is a convenience widget that combines common painting, positioning, and sizing of widgets. A Container class can be used to store one or more widgets and position it on the screen. It is like a box to store contents.

Ticker is a special periodic timer that we can use to be notified when the Flutter engine is about to draw a new frame. To create a ticker, we need to add a SingleTickerProviderStateMixin to our State subclass.

There are several ways to handle user input in Flutter, depending on the type of input and the desired behavior. Some common options include:

• Using a TextField widget for text input, with a TextEditingController to handle the input value
• Using a Button widget for button clicks, with an onPressed callback to define the desired behavior
• Using a Form widget to validate and handle input from multiple fields

Hot restart loads code changes into the VM, and restarts the Flutter app, losing the app state.

Full restart restarts the iOS, Android, or web app. This takes longer because it recompiles the Java / Kotlin / ObjC / Swift code.

• Lack of Third-Party Libraries and Widgets: Flutter is not too old unlike its contemporaries and lacks the presence of third-party libraries.
• Issues with iOS: Flutter is developed by Google. This is why developers are worried about its implementation for iOS.
• Large File Sizes: One big loophole that ois hard to ignore is the large file size of apps developed in Flutter. In some cases these file sizes could be a significant issue.

A Provider allows to not only expose a value, but also create/listen/dispose it. When you place a Provider widget in your widget tree all the Childs of the Provider will have access to the values exposed by it.

Null-aware operators are used in almost every programming language to check whether the given variable value is Null. The keyword for Null in the programming language Dart is null. Null means a variable which has no values assign ever and the variable is initialized with nothing like.

To create HTTP requests, use the HTTP package (import 'package:http/http.dart' as http;). In the following manner, we can make the Requests:

http.get(‘https://jsonplaceholder.typicode.com/albums/1‘);  

It will return a Future <http.Response>.

It is compulsory to know the Dart language to use Flutter. Flutter applications make use of the Dart language for coding mobile phone apps.

The most useful editors for Flutter apps are Visual Studio, Android Studio, Xcode, IntelliJ IDEA, Eclipse, Vim, and Emacs.

You can learn flutter from Flutter Documentation available as open source on Google.