App_development55555555555555555555.pptx

Application development

1. Dart Programming Sameeha moogab 2024

2. Outline What is Dart

3. What is Dart Dart is for Scalable, productive app development. Dart is an open-source, scalable programming language , with robust libraries and runtimes , for building web, server, and mobile apps .

4. Dart Basic Concepts Everything you can place in a variable is an object , and every object is an instance of a class. Even numbers, functions, and null are objects. All objects inherit from the Object class. Specifying static types clarifies your intent and enables static checking by tools, but it’s optional. The variables with no specified type get a special type: dynamic .)

5. Dart Basic Concepts Unlike Java, Dart doesn’t have the keywords public, protected, and private. If an identifier starts with an underscore (_), it’s private to its library. Identifiers can start with a letter or _ , followed by any combination of those characters plus digits.

6. Basics - Dart Program // Entry point to Dart program void main() { helloDart (); } void helloDart () { print('Hello, Dart!’); } main() - The special, required, top-level function where app execution starts. Every app must have a top-level main() function , which serves as the entry point to the app.

7. Comments Dart supports both single line and multi line comments // Single line comment /* This is an example of multi line comment */

8. Variables Variables are declared using var keyword similar to JavaScript. var name = 'Bob'; Variables are references. Uninitialized variables have an initial value of null. Even variables with numeric types are initially null, because numbers are objects.

9. Data Types in Dart There are a few key places that you need to know about types for now, and the rest will be covered in time. First, when declaring variables, you give them a type: number int - Integer values, which generally should be in the range -253 to 253 double - 64-bit (double-precision) floating-point numbers, as specified by the IEEE 754 standard string boolean – true and false symbol Collections list (arrays) map Queue The type always comes before the value it describes. String name; int age; Using types prevents you from assignin g values to variables that aren’t compatible : int greeting = 'hello'; If you try to compile that file by running it in your terminal, you’ll get error:

10. Dynamic Types You can define untyped variables by declaring them using the ‘var’ or ‘dynamic’ keywords. The ‘var’ keyword declares a variable without specifying its type, leaving the variable as a dynamic. var myString = 'Hello'; The ‘dynamic’ keyword declares a variable of the type ‘ dynamic’with optional typing. dynamic myNumber = 'Hello';

11. String Interpolation Identifiers could be added within a string literal using $identifier or $ varaiable_name syntax. var user = 'Bill'; var city = 'Bangalore'; print("Hello $user . Are you from $city ?"); // prints Hello Bill. Are you from Bangalore? You can put the value of an expression inside a string by using ${expression} print('3 + 5 = ${3 + 5}'); // prints 3 + 5 = 8 In Dart, normally you can add escape characters to format your string.For example: ‘\n’ means ‘new line’. main(){ print('this\ nstring \ nhas \ nescape \ ncharacters ’); } Print dollar Sign using \$ this string has escape characters output double price = 100.75; print('Price is: \$${price}'); Price is: $100.75 output

12. Collection Perhaps the most common collection in nearly every programming language is the array, or ordered group of objects. In Dart, arrays are List objects , so we usually just call them lists. var numbers = [1,2,3,4,5]; var cities = ['Bangalore', ‘Kolkata', ‘Chennai'];

13. Operators There aren’t any big surprises in Dart operators, There aren’t any big surprises in Dart operators,

14. THE ?. OPERATOR Suppose you want to call an API and get some information about a User. And maybe you’re not sure whether the user information you want to fetch even exists. the null-aware operators make it much easier. The following operator basically says, “Hey, assign userAge to user.age . But if the user object is null, that’s okay. Just assign userAge to null, rather than throwing an error” void getUserAge (String username) async { final request = UserRequest (username); final response = await request.get (); User user = new User.fromResponse (response); this.userAge = user ?. age ; // etc. }

15. THE ?? OPERATOR The second null-aware operator is perhaps even more useful. Suppose you want the same User information, but many fields for the user aren’t required in your database. There’s no guarantee that there will be an age for that user. Then you can use the double question mark ( ?? ) to assign a “fallback” or default value. void getUserAge (String username) async { final request = new UserRequest (username); final response = request.get (); Useruser = new User.fromResponse (response); this.userAge = user.age ?? 18; This operator basically says, “Hey, if this object is null , then assign it to this value. If it’s not, just return the object as is”

16. Control flow if and else var age = 17; if (age >= 18){ print('you can vote'); } else { print('you can not vote'); } curly braces { } could be omitted when the blocks have a single line of code var age = 17; if(age >= 18) print('you can vote'); else print('you can not vote');

17. Control flow else if Supports else if as expected var income = 75; if (income <= 50){ print('tax rate is 10%'); } else if(income >50 && income <80){ print('tax rate is 20%'); } else{ print('tax rate is 30%'); } curly braces { } could be omitted when the blocks have a single line of code if (income <= 50) print('tax rate is 10%'); else if(income >50 && income <80) print('tax rate is 20%'); else print('tax rate is 30%');

18. loops Supports standard for loop (as supported by other languages that follow C like syntax) for (int ctr=0; ctr<5; ctr++){ print(ctr); } Iterable classes such as List and Set also support the for-in form of iteration var cities = [' Kolkata','Bangalore','Chennai','Delhi ']; for(var city in cities){ print(city); } Iterable classes also support forEach method var cities = [' Kolkata','Bangalore','Chennai','Delhi ']; cities. forEach ((city) => print(city));

19. WHILE LOOPS while loops evaluate the condition before the loop runs—meaning it may never run at all while( someConditionIsTrue ) { // do some things } do-while loops, on the other hand, evaluate the condition after the loop runs. So they always execute the code in the block at least once: do { // do somethings at least once } while( someConditionIsTrue );

20. switch case Switch statements compare integer, string, or compile-time constants using == Enumerated types work well in switch statements Supports empty case clauses, allowing a form of fall-through var window_state = 'Closing'; switch( window_state ){ case 'Opening': print('Window is opening'); break; case 'Opened': print('Window is opened'); break; case 'Closing': print('Window is closing'); break; case 'Closed': print('Window is closed'); break; case 'Terminated': print('Window is terminating or terminated'); break;}

21. TERNARY OPERATOR The ternary expression is used to conditionally assign a value. It’s called ternary because it has three portions —the condition, the value if the condition is true, and the value if the condition is false: This code says, “If this user’s title is ‘Boss,’ change her name to uppercase letters. Otherwise, keep it as it is.”

22. Functions The function signature follows this pattern: ReturnType functionName ( ArgumentType arg ) . And every function that uses return must have a return type—otherwise, its return type is void. It’s important to note that Dart is a true object-oriented language. Even functions are objects, with the type Function . You can pass functions around and assign them to variables. Languages that support passing functions as arguments and returning functions from functions usually refer to these as higher-order functions.

23. Functions Dart also supports a nice shorthand syntax for any function that has only one expression . In other words, is the code inside the function block only one line? Then it’s probably one expression, and you can use this syntax to be concise: String makeGreeting (String name) => 'Hello, $name’; we’ll call this an arrow function . Arrow functions implicitly return the result of the expression. => expression; is essentially the same as { return expression; } . There’s no need to (and you can’t) include the return keyword.

24. Parameters Dart functions allow positional parameters, named parameters, and optional positional and named parameters, or a combination of all of them. void debugger(String message, int lineNum ) { // ... } To call that function, you must pass in a String and an int, in that order: debugger('A bug!', 55); Named parameters are written a bit differently. You wrap any named parameters in curly braces ( { } ). This line defines a function with named parameters: void debugger({String message, int lineNum})

25. you can pass positional parameters that are optional , using [ ] : int addSomeNums (int x, int y, [int z] ) { int sum = x + y; if (z != null) { sum += z; } return sum; } You can define default values for parameters with the = operator in the function signature: addSomeNums (int x, int y, [int z = 5] ) => x + y + z;

26. Object oriented in Dart When writing Dart code, you’ll likely want to create separate classes for everything that can represent a real-world “thing.” Consider if we were writing a point-of-sale (POS) system used to sell goods to customers. What kinds of classes do you think you’d need to represent “things” (or data)? What kind of “things” does a POS app need to know about? Perhaps we need classes to represent a Customer, Business, Employee, Product, and Money . Those are all classes that represent real-world things.

27. Class class Employee{ String firstName ; String lastName ; int age; double salary; } main(){ var emp = new Employee(); emp.firstName = "Lars"; emp.lastName = " Bak "; print( emp.firstName ); print( emp.lastName ); }

28. Class constructor class Employee{ String firstName ; String lastName ; int age; double salary; Employee( this.firstName , this.lastName , this.age , this.salary ); } main(){ var emp = new Employee('Lars','Bak',45,550.67); print( emp.firstName ); print( emp.lastName ); print( emp.age ); print( emp.salary ); } You can give classes special instructions about what to do assoon as a new instance is created. These functions are called constructors .

29. Inheritance In object-oriented programming, inheritance is the idea that a class can inherit or subclass a different class. A cat is a specific kind of mammal, so it follows that a cat will have all the same functionality and properties as all other mammals . You can write a Mammal class once, and then both the Dog and Cat classes can extend the Mammal class. class Cat extends Mammal {} class Eric extends Human {} class Honda extends Car {} When a class inherits from another class (called its superclass ), it’s essentially a copy of the superclass, and you can add extra functionality—whatever you define in the class itself.