Flutter | Dart | Tips and tricks

1. C - Comments
1. /// for the documentation or multiple line. When press enter next line will be comments and VS Cose generate ///
2. // for single line comment. 
2. C - Constant
1. Can const be null? if null can const change later?
3. C - Class
1. Every class is a subclass of the object class.
2. _myVariable - An underscore (_) at the beginning indicates that it is a private variable.
3. Properties of the Object.
1. runtimeType - Check the type of the instance of the object/variable during runtime (not compile time).
4. Why and how can I use the toSting() method. 
1. Because your class is a subclass of the Object class (Super Class).
5. What is the meaning of the annotation @override?
1. This does not overwrite. This re-implements the superclass method at compile time.
2. Use when
1. Overriding a method from a parent class.
2. Implementing a method defined in an interface.
3. Why @override is not needed in an extension?
6. What is singleton class?
1. One instance and provides a global point of access to that instance.
2. In Dart three layer deep.
7. print() and toString() relation. 
1. In Dart, the toString() method is automatically (implicit) called during print(). In addition, toString() is also a method of the Object superclass.
8. How can a property have both a getter and a setter behavior?

1. void main() {
     var myCar = Car();
     print(myCar.speed); // Getter
     myCar.speed = 20;   // Setter
     print(myCar.speed);
   }
   
   class Car {
     int speed = 0;  // Property
     
   }
   

2. Here this property has no control 
9. Why use static?
1. Static getters can be accessed without creating an instance of the class.
   
10. Constructor tips
1. A constructor is a special function that does not have a return type, not even void. 
2. It can be overloaded by using different parameters, allowing for multiple ways to create an instance of a class. 
3. This function may have a body.
4. Constructors are not inherited by default. So when you create a subclass, you need to explicitly define its superclass constructor.
1. class Mom extends Person {const Mom() : super(role: Role.mom);}
1. Super class constructor must call it form the subclass using super keyword.
   
2. class Mom extends Person { const Mom({required super.role});}
1. By using super.role, the Mom constructor passes the role parameter directly to the Person constructor.
11. Factory Constructor
1. Factory constructors are special methods that allow you to return (create) an instance of a class (or a subclass) without being required to return a value in the same way a typical function does. 
1. factory Vehicle.truck() => Truck();
2. print(Vehicle.truck()); // It creates subclass Truck instance;
   
2. Even if it could return a void, the factory constructor's purpose is to return an instance of Vehicle.
3. Return an existing instance rather than creating a new one each time.
12. Why mixin is used?
1. Directly, multiple inheritance is not supported in Dart. Therefore, hierarchical inheritance is possible (not a good idea), but a class cannot inherit from more than one class at the same time. Dart uses a mixin-based approach to achieve similar functionality.
13. ... (Spread Operator) VS .. (Casade Notation)
14. Why use const before a constructor?
15. Wha is efficient lookup, lookup table and hash table?
16. Dart can't create a range. How can we solve this issue?
1. We have to bild custom rang function.
17. Why you need to learn generics?
1. final double doubleValue = getDoubleValue();
1. Call site accept the double value;
2. For user readability, the generic name can be either E (Element) or T (Generic Type).
3. bool typesMatch<L, R>(L a, R b) {   return a.runtimeType == b.runtimeType; //L==R; }
1. a and b are the actual objects you pass into the function. These objects must be instances of types that L and R represent.
2.  The objects a and b could be any objects that are of types L and R, respectively, and these types could be extended from Object (which all Dart classes inherently do).
3. L and R  are generic type parameters.
   
18. What is the difference between errors and exception?
1. Error
   
1. Errors are not meant to be caught
   
2. Never try an error (catch).
3. Predefined (documented) and system crashes.
2. Exception
1. Exception are meant to be caught.
2. Keyword try, catch and throw.
3. An exception is a class and a condition where the program can recover. You throw an instance of an exception using throw keyword.
19. What is typedef?
1. For typedef, function signatures are mainly used as function parameters.
20. What is StreamController?
1. Just an object creating a stream with the add, addError, or close functionality.
21. Dart promotional conversion?
1. T operator +(T? other) { final thisShadow = this; if (thisShadow != null && other != null) { return thisShadow + other as T; } why final thisShadow = this; is use?

L - Linter

For specific problems

F - Function 

1. What is Predicate?
1. Is a function return true or false.

O - Operator

1. ? (Null-aware Operator) Vs ! (Null Assertion Operator) Vs ??
1. Null-aware Operator(?) - Safely access a property or method of an object that might be null, without throwing an error if it is null.
1. String? name; int? length = name?.length; // length will be null if name is null
2. Null Assertion Operator(!) - A value must not be null; otherwise, it will throw a NoSuchMethodError.
1. String? name; if (name != null) { print(name!); } // Commonly used when you have checked for null
2. How is the datatype modifier determined by Dart?
1. Like final a = 10/5; // it would be double
2. like final a = 10*5; It would be int;
3. Flip operator
1. Boolean Flip 
1. myValue = !myValue;
2. Bitwise Flip
1. var flipped = ~num;
3. Flipping an Iterable or List
4. Flipping Key-Value Pairs in a Map

S 

1. State Management 
1. Provider, Riverpod, and Bloc 
1. Bloc is complex but separate business form UI. Good for async and well-structured for larger applications with complex state management.

T - Tips 

1. Most of the time, mobile apps don’t need a Save button.

V - Variable

The variables can involve different modifies const, final var or dynamic. These keywords control the behaviors of the variables in terms of mutability, type safety and initialization. var is the default modifier.

• Can a const value be assigned to a final variable?
• Yes, you can assign a const value to a final variable.
• const age = 25; final ageYear = age; // Valild
• It is assigned once, but it's a constant value of type int at runtime.
• Can a const value be assigned to a final variable?
• No, you can assign a final value to a const variable.
• final age = 25; const ageYear = age; // Invalild
• Can a const value be assigned to a const variable?
• Yes, you can assign a const value to a const variable.
• const age = 25; const ageYear = age; // Valild
• What is type promotion?
• Less precision
• final a = 10;
• More precision (type promotion)
• final int a = 10; 

C - Constant

1. Can const be null? If null is accepted, can const change later?
1. Yes, const can be null only if type is nullable. No, const values are immutable and cannot be changed once set, regardless of whether the value is null or not. The value of a const variable must be known at compile time, and once set, it cannot be modified.  Can't change internally or assign a new value (can share). const int? a = null; // 'a' is a compile-time constant and nullable 
2. const don't allow mutability. 
3. const don't allow mutability
1.  const constAge = 10; final finalAge = 20; constAge = finalAge; //Not allowed.  

const a =10; const b =a; // Allowed. 

•  F -Final

1.   Can't assign a new value but can change(mutation) internally (can't share). It is a runtime constant. 
2. final Allows Mutation of Variable Contents
1. const constAge = 10; final finalAge = 20; finalAge = constAge; // allowed
2. It's basically constant so 
1. final a = 50; a=10;//Not allowed.
2. 
   

• V- Var

1. Initially, the datatype of a variable declared with var is implicitly determined at compile time in Dart.
2. The assigned value can be changed at runtime, and it can also be modified internally.
3. var is the default modifier.
4. Inferred means automatically deduced or figured out by the system.

W - Widget

1. What is WidgetBuilder?
1. It is a function that accepts context(BuildContext) as a parameter and returns dynamic widget(s).
2. BuildContext Vs WidgetBuilder Vs ItemBuilder Vs Builder  [Dynamic nature]
1. BilderContext - Can allow access to other widgets and properties of the tree. It also holds the location of a widget | object.
2. WidgetBuilder - Create a new widget (single) based on the BuilderContext | function.
1. typedef WidgetBuilder = Widget Function(BuildContext context);
3. ItemBuilder-  Create a new list of widgets (ListView, GridView where each item is intexed) based on the BuilderContext location representations | function.
1. typedef ItemBuilder = Widget Function(BuildContext context, int index);
4. Builder - Create a new child [widget] using the WidgetBuilder function based on the BuildContext parameter | widget.
3. What is FutureBuilder?
4. StreamBuilder
1. Data cannot be held even when an interruption occurs. StreamBuilder retains data during interruptions.