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What are some common Flutter performance optimization techniques?

Flutter provides many tools and techniques to improve the performance of your app. Here are some of the common tools and techniques:

Minimize UI rebuilds: Use the const and final keywords for UI elements that don’t change, and use the shouldRebuild method to control when a UI element is rebuilt.
Reduce the size of widgets: Use the SizedBox tool to create an empty space and the Spacer tool to fill the space. Use the Expanded tool to expand a sub-tool to fill the available space.
Use the right tools: Use StatelessWidgets for widgets that don’t change, and StatefulWidgets for widgets that change. Use AnimatedBuilder to create animations, and use FutureBuilder to handle asynchronous data.
Reduce unnecessary layers: Use the ClipRRect tool to clip UI elements to a specific shape, and use the RepaintBoundary tool to isolate expensive UI elements from the rest of the UI element tree.
Minimize costly operations: Use the const keyword for variables that don’t change, and use the const constructor for things that are created once and never change. Use lazy loading to defer costly operations until they’re needed.
Use the right data structures: Use the Set and Map data structures to perform efficient searches and comparisons, and use the List data structure for ordered sets.

By following these techniques, you can improve the performance of your Flutter app and provide a great user experience.

What is the difference between StatelessWidget and StatefulWidget in Flutter?

In Flutter, StatelessWidget and StatefulWidget are two different types of widgets that are used to create UI elements.

A StatelessWidget is a widget that does not have any mutable state. Once created, its properties cannot be changed. Examples of StatelessWidget include text, icons, and images.
A StatefulWidget is a mutable stateful widget. It can change its properties based on user interactions. Examples of StatefulWidget are TextField, Checkbox, and Slider.

What is the difference between MaterialApp and WidgetsApp in Flutter?

MaterialApp and WidgetsApp are two different types of apps in Flutter.

MaterialApp is used to create applications that follow the material design guidelines. It provides pre-built UI elements that follow the material design specifications, such as AppBar, BottomNavigationBar, and FloatingActionButton.
On the other hand, WidgetsApp is used to create apps that do not follow the Material Design guidelines. It provides a simple set of tools that can be used to create custom widgets.

What is state in Flutter?

In Flutter, state refers to data or information that can change dynamically during the life of a widget. Widgets are the building blocks of a Flutter application, and can be either stateful or stateless.

Stateful UI elements maintain state information and can update their state when needed. State is managed by a separate object known as a state object. The state object is created when a stateful UI element is inserted into the UI element tree and is destroyed when the UI element is removed from the tree.

What is the purpose of Scaffold widget in Flutter?

Scaffold is used to build the infrastructure of a Material Design app in Flutter. It provides a top navigation bar, bottom navigation bar, and a text widget. Scaffold also provides some important features like drawer support, floating action button support, and Snackbar support. It is the most used tool to build the infrastructure of a Material Design app in Flutter.

What is the purpose of the BuildContext parameter in the build() method of a widget in Flutter?

The BuildContext parameter is used to access the widget tree and perform actions such as building or updating widgets. The BuildContext object represents the location of the widget in the widget tree. It provides access to the closest ancestor of the BuildContext, which can be used to access properties of the ancestor widget or its children. The BuildContext parameter is required in the build() method of a widget because it is used to build the user interface for the widget and its children.

What is the difference between push and pushReplacement methods in Flutter?

In Flutter, push and pushReplacement are two methods used to navigate between different screens in an app. Both methods are available in the Navigator class, which manages the navigation set in a Flutter app.

The push to push a new track into the navigation group, adding a new screen to the app’s UI. This method does not remove the previous screen from the group, meaning the user can use the back button or swipe gesture to return to the previous screen.
The pushReplacement is similar to the push method, but it replaces the current screen in the navigation group with a new screen. This means that the previous screen is removed from the group and cannot be returned to using the back button or swipe gesture.

What is the purpose of MediaQuery widget in Flutter?

MediaQuery is used to retrieve information about the device’s screen size and orientation in a Flutter app. MediaQuery provides properties like devicePixelRatio, orientation, and size, which can be used to create responsive UIs that adapt to different screen sizes and orientations.

For example, a developer can use the size property of a MediaQuery widget to adjust the font size of a text widget based on the device’s screen size.

What is the purpose of SafeArea in Flutter?

The SafeArea tool is used to ensure that content is displayed within a safe area of the screen that is not obscured by the device’s system user interface, such as the status bar or navigation bar.

SafeArea is useful for creating user interfaces that need to be displayed on devices with different screen sizes or aspect ratios. It ensures that important content is not hidden by the device’s system UI, which can improve the user experience.

What is the purpose of the Expanded widget in Flutter?

The Expanded tool is used to expand a subtool to fill the space available within a parent tool. The Expanded tool is typically used in a Row or Column tool to distribute space evenly among its children. For example, if a Row tool has three subtools, and one of the subtools is wrapped in an Expanded tool, that subtool will expand to fill any space left in the row after the other two subtools are sized.

What is the purpose of Flex widget in Flutter?

The Flex tool is used to create a flexible container that can be used to create complex layouts in a Flutter application. The Flex tool provides properties like direction, mainAxisSize, and mainAxisAlignment, which can be used to control the layout of its sub-elements.

For example, a developer can use the orientation property of a Flex widget to create a horizontal or vertical layout and use the mainAxisAlignment property to align its sub-elements to the beginning, center, or end of the container.

What is Stream in Flutter?

A stream is a series of asynchronous events that can be listened to and responded to. Streams provide a way to handle asynchronous data flows, such as data from the network or user input.

Streams in Flutter are based on the Dart Stream API, which provides a set of classes and methods for working with streams. The basic concept of the Stream API is that it separates the data producer from the data consumer. The data producer pushes data to the stream, while the data consumer listens to the stream and responds to events as it streams.

In Flutter, streams are typically used to handle data from sources that emit events over time, such as user input, network responses, or device sensors. Streams are also used to handle animations and other dynamic UI elements that require constant updates.

What is the purpose of the Wrap widget in Flutter?

The Wrap tool is used to create a layout that wraps its sub-elements to the next line when there is not enough space to display them on a single line.

Wrap is useful for creating user interfaces that need to display a large number of elements that cannot fit on a single line. It ensures that elements are displayed in a way that maximizes the available space.

What is the purpose of Hero widget in Flutter?

The Hero widget is used to create a transition between two widgets with the same tag in a Flutter app. The Hero widget is useful for creating UIs that need to transition between two screens or parts of the same screen. It provides smooth animations that help the user understand the relationship between the two widgets.

What is the purpose of AnimatedContainer in Flutter?

The AnimatedContainer is used to animate changes to its properties in a Flutter application. The AnimatedContainer provides several properties, such as duration and curve, that can be used to control the animation. For example, a developer can use the AnimatedContainer to animate changes to the size or color of a widget in response to user input or other events in the app.

What is the purpose of AnimatedBuilder in Flutter?

AnimatedBuilder is used to create custom animations in a Flutter application. AnimatedBuilder provides a build function that can be used to create a custom widget tree that can be animated. For example, a developer can use AnimatedBuilder to create a custom widget tree that animates changes in the position or rotation of a widget in response to user input or other events in the application.

What is the purpose of ConstrainedBox widget in Flutter?

The ConstrainedBox widget is used to create a widget with constraints in a Flutter application. The ConstrainedBox widget provides properties, such as minWidth, maxWidth, minHeight, and maxHeight, which can be used to control the constraints of the widget.

For example, a developer could use the ConstrainedBox UI element to create a UI that displays an image at its maximum width and height.

What is the purpose of ShaderMask in Flutter?

The ShaderMask tool is used to apply shaders to a widget in a Flutter app. The ShaderMask tool provides properties, such as shader and blendMode, that can be used to control how the shader is applied to the widget. For example, a developer can use the ShaderMask tool to apply a gradient shader to a widget, creating a gradient effect.

What is the purpose of the InheritedWidget widget in Flutter?

The InheritedWidget widget provides a mechanism for passing data down the widget tree without having to explicitly pass the data as constructor arguments or method parameters.

For example, a developer could use the InheritedWidget widget to provide a theme object that can be accessed by all of the descendant widgets in the widget tree.

What is the purpose of the ValueListenableBuilder widget in Flutter?

The ValueListenableBuilder widget provides a builder function that can be used to rebuild a widget tree when the value of a ValueListenable object changes.

For example, a developer could use the ValueListenableBuilder widget to rebuild a widget that displays the current value of a counter object when the value of the counter object changes.

What is the purpose of the StreamBuilder widget in Flutter?

The StreamBuilder widget provides a builder function that can be used to rebuild a widget tree when data is emitted by a Stream.

For example, a developer could use the StreamBuilder widget to rebuild a widget that displays the latest news articles when new articles are published to a news feed.

There are two types of streams:

Single Subscription streams which convey events in chronological order.

Broadcast streams which provide data right after subscribe to that event.

What is the purpose of the LayoutBuilder widget in Flutter?

The LayoutBuilder widget provides a builder function that can be used to rebuild a widget tree when its parent widget changes size. For example, a developer could use the LayoutBuilder widget to rebuild a widget that adjusts its layout based on the size of its parent widget.

What is the purpose of FutureBuilder in Flutter?

FutureBuilder is used to rebuild a widget when a Future is completed in a Flutter application. FutureBuilder provides a build function that can be used to rebuild a widget tree when a Future is completed. For example, a developer can use FutureBuilder to rebuild a widget that displays the data returned by a Future after it is completed.

Talk about different build modes in Flutter.

Debug mode is used to debug the application on the physical device, emulator, or simulator.
Profile mode is used to analyze the performance of your app. Here, some extensions and tracing are enabled.
Release mode is enabled to deploy your app. Here, assertions, service extensions, and debugging are disabled.

What is Tree shaking?

Tree shaking is an optimization technique to remove the unused module in the bundle during the build process. It is a dead code elimination technique used to optimize the code.

What do you understand from hot reload and hot restart?

Hot reload means injecting the updated source code files into running Dart VM (Virtual Machine). The Hot reload process does not add only new classes but it also adds properties, fields, and methods to existing classes, and changes existing functions.

Hot restart works by resetting the app’s current state to the app’s initial state.

Explain the lifecycle of a Stateful Widget.

createState
initState
didChangeDependencies
build
didUpdateWidget
setState
deactivate
dispose

Why is the Android and iOS folder in the Flutter project?

Android: This folder holds a complete Android project. It is used when you create the Flutter application for Android. When the Flutter code is compiled into the native code, it will get injected into this Android project, so that the result is a native Android application. For Example: When you are using the Android emulator, this Android project is used to build the Android app, which is further deployed to the Android Virtual Device.

iOS: This folder holds a complete Mac project. It is used when you build the Flutter application for iOS. It is similar to the Android folder, which is used when developing an app for Android. When the Flutter code is compiled into the native code, it will get injected into this iOS project, so that the result is a native iOS application.

What types of tests can you perform in Flutter?

Unit Tests: It tests a single function, method, or class. Its goal is to ensure the correctness of code under a variety of conditions. This testing is used for checking the validity of our business logic.

Widget Tests: It tests a single widget. Its goal is to ensure that the widget’s UI looks and interacts with other widgets as expected.

Integration Tests: It validates a complete app or a large part of the app. Its goal is to ensure that all the widgets and services work together as expected.

What is the use of Ticker in Flutter?

We use a ticker to tell how often our animation is refreshed in Flutter.

What is the use of Mixins?

Multiple inheritances are not supported by Dart. Thus, we need mixins to implement multiple inheritances in Flutter/Dart. The use of mixins makes it easy to write reusable class code in multiple class hierarchy levels.

What is the purpose of keys in flutter?

Keys are important for:

Preserving State: Flutter uses keys to preserve the state of widgets when they are moved in the widget tree.
Reordering Widgets: If you reorder or filter lists, keys ensure that the correct widget keeps its data or state.
Accessing State: GlobalKey allows you to access the state or methods of a widget from outside its class.

When to Use Keys

Use GlobalKey when you need to access a widget’s state from outside or when you want to uniquely identify a widget across the entire app.
Use ValueKey or ObjectKey (Types of LocalKeys) when working with dynamic lists where you want to maintain the state of individual items even when their order changes.
Use UniqueKey if you want to force a widget to rebuild and be treated as a completely new widget.

What is state management?

Using it, states of various UI controls are centralized to handle data flow across an application. It can be a text field, radio button, checkbox, dropdown, toggle, form, and so on. In Flutter, state management can be categorized into two types as follows:

Ephemeral State: Ephemeral state is also called UI state or local state, and it pertains to a particular widget. In other words, it is a state that is contained within the specific widget. By means of StatefulWidget, Flutter provides support for this state.
App State: This is different from the ephemeral state since it is a state that we intend to share across different parts of the app and which we want to maintain between sessions. These types of states can thus be used globally. By means of scoped_model, Flutter provides support for this state.

Explain Flutter Provider.

The provider package is an easy-to-use package which is basically a wrapper around the InheritedWidgets that makes it easier to use and manage. It provides a state management technique that is used for managing a piece of data around the app.

What is await in Flutter?

Until the async method is finished, await interrupts the process flow.

Conclusion:

By preparing for a wide range of questions — from basic widgets and state management, you’ll be well-equipped to impress in any Flutter interview. When you’re interviewing for your first Flutter role. But if you are looking to level up your career, you have to go through our story of advanced topics like performance optimization and platform-specific integration.
“Advanced level Flutter Interview Questions For Cracked any Dart Interview”. By Hamza Asif

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Top Flutter Interview Questions 2024 for passing any Intermediate level Test

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Conclusion:

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Written by Hamza Asif

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