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Null-aware operators in dart allow you to make computations based on whether or not a value is null. Dart provides some useful information to handle the null values.  

• The "??=" assignment operator: It assigns a value to a variable only if it is null.

• The "??" null-aware operator: This one computes and returns the value between two expressions. In the first step, expression 1 is checked for nullness, and if it is, its value is returned; otherwise, expression 2 is evaluated, and its value is returned.

• The “?.” Safe Navigation Operator: It is also known as the Elvis operator. It is possible to USE the ?. operator when calling a method/getter on an object, as long as the object isn't null (otherwise, the method will return null).

Flutter is a MOBILE TECHNOLOGY that is among the most innovative and booming in the mobile market as the next revolutionary thing right now. Although it is a relatively new framework for developing cross-platform applications, its popularity is soaring due to which there is an INCREASE in demand for Flutter developers. 

• Container: In this parent WIDGET, multiple child widgets can be easily controlled and handled by adjusting their size, PADDING, and color efficiently. We can wrap a widget in a container widget if it needs any styling, like a color, a shape, or a size constraint, etc.
• SizedBox: This is a specific size box. It does not allow us to SET the widget's color or decoration, unlike Container. In this case, we only need to resize the widget that is PASSED as a child. In other WORDS, it forces its child widget to have a specific size. 

Until the async method is finished, await interrupts the PROCESS flow. Await generally MEANS: Wait here until this FUNCTION is finished so that you can get its return VALUE. Await can only be used with async. Using this, all currently running functions are put on HOLD until PF nature is complete. 

The provider is built using widgets. You can use all the OBJECTS in the provider as if they were just part of Flutter with the new widget subclasses it creates. This also means that the provider is not cross-platform. The provider is the SIMPLEST way to handle state management. Basically, it works on the concept of PUB-SUB i.e., there is one provider and SEVERAL subscribers.

As far as Flutter is concerned, the following database packages are widely ACCEPTED and mostly used:  

Firebase database: It gives users access to and control over the cloud database. Firebase basically provides a NoSQL database for Flutter apps with the ability to manage DATA retrieval and STORAGE through JSON protocol. Data sync and quick loading make it one of the most suitable options for Flutter Apps. 
Features:

• NoSQL DB 
• APIs (REST only) 
• Authentication
• Analytics 
• Storage 

SQFlite database: Users can access and modify the SQLite database using this. With this database, you have FULL control over your database, queries, relationships, and anything you could desire. 
Features: 

• Serverless 
• Zero configuration 
• Open-Source 
• Compact 
• Single DB file 

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

It will RETURN a Future <http.Response>.

The SHORTENED VERSION of in-between animation is TWEEN animation. The start and endpoints of an animation must be specified in tween animation. USING this method, the animation can begin at the beginning and can progress through a series of values until it reaches the endpoint. TRANSITION speed and duration are also determined by using the tween animation. Calculating the transition from the beginning to the end will be easier with the widget framework. 

The pubspec.yaml file, also known as 'pubspec', is a file that is INCLUDED when you CREATE a Flutter project and is located at the TOP of the project tree. This file contains information about the dependencies like packages and their VERSIONS, fonts, etc., that a project requires. It makes sure that the next time you build the project, you will get the same package version. Additionally, you can set constraints for the app. During working with the Flutter project, this CONFIGURATION file of the project will be required a lot. This specification is written in YAML, which can be read by humans.  

The following are included in this file: 

• General project settings, like name of the project, version, description, etc.   
• Dependencies within a project.   
• The assets of the project (e.g., images, audio, etc.). 

Whether you are BUILDING a mobile app or a web application, State Management is crucial. 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. 

The following diagram gives a BETTER explanation of the differences between ephemeral and app states:

FLUTTER supports three types of tests:

• Unit tests: Using unit testing, you can test a class or method. Unit tests do not check for rendering to screen, interacting with external services, or user interactions.   
• Widget tests: Using widget testing, you can test a single widget.  This ensures that the widget's UI LOOKS as expected and responds APPROPRIATELY to events. In other WORDS, it ensures that the widget design, rendering, and interaction with other widgets are up to the mark.   
• Integration tests:  Using Integration testing, you can test the critical flows of the entire app. It is important to check whether all widgets and services work together as expected. You can also use it to MEASURE and benchmark the performance of your app. 

BuildContexts are used to identify or locate WIDGETS in widget trees. Each widget has its own BuildContext, i.e., one BuildContext per widget. Basically, we're USING it to FIND references to other widgets and themes. In ADDITION, you can utilize it to interact with widget parents and ACCESS widget data. 

For any dart application, the initial execution requires a fair amount of TIME. Therefore, to solve this problem, flutter has two features: Hot Reload and Hot Restart, which reduce the execution time of our app after we run it. 

• Hot Reload: It is considered an excellent feature of flutter that takes approximately one second to PERFORM its functionality.  With this function, you can make changes, fix bugs, create UIs, and add features easily and quickly. By utilizing the hot reload feature, we can quickly compile the new code in a file and SEND it to Dart Virtual Machine (DVM). As soon as DVM completes the update, it updates the app's UI. The preserved STATE is not destroyed in hot reload.
• Hot Restart: It has a slightly different functionality as compared to a hot reload. In this, the preserved states of our app are destroyed, and the code gets compiled again from the beginning. Although it takes longer than a hot reload, it's FASTER than a full restart function.

A Flutter SDK (Software Development Kit) enables developers to build applications for MOBILE, web, and desktop using a single codebase. Flutter SDK includes the following features:  

• DART SDK   
• Contains a rendering engine, widgets, APIs for testing and integration, etc.  
• Compilation tools for Native Machine Code (code for IOS and Android).    
• React-style modern framework  
• Provide Interop and plugin APIs to connect with system and 3rd-party SDKS.   
• A headless test runner that runs tests on Windows, Linux, and Mac.  
• Use the Dart DevTools to test, debug, and profile your app. Use  
• Flutter and Dart command-line tools to develop, build, test and compile your apps across platforms.   

The streams’ functionality is part of Dart and is inherited by Flutter. In Flutter, there are two kinds of streams: 

• Single Subscription Streams: These streams deliver events sequentially. They are considered as sequences CONTAINED within a larger whole. These streams are used when the order in which events are received matters, such as reading a file. There can be only one listener throughout the sequence, and WITHOUT a listener, the EVENT won't be triggered. 
• Broadcast Streams: These streams deliver events to their subscribers. Upon subscribing to events, subscribers are immediately able to start listening to them.  These are versatile streams that allow several listeners to listen simultaneously. FURTHERMORE, one can listen again even after canceling a previous subscription.

In asynchronous programming, streams are used to provide a sequence of data in an asynchronous manner. Similar to a pipe, we PUT a VALUE on one end and a LISTENER receives it on the other. Several listeners can be put into one stream, and they'll all get the same value when they're put in the pipeline. It's possible to create and manage streams through the SteamController. 

The Stream API provides the await for and LISTEN() methods for processing streams. Streams can be created in MANY ways, but they can only be used in the same manner. Here is an example: