Fundamental knowledge about Flutter and Dart
- what is a dart?
Dart is an object-oriented programming language developed by Google. Whilst technically not restricted, it’s primarily used for creating frontend user interfaces for the web (with AngularDart or Flutter for Web) and mobile apps (Flutter). It’s under active development, compiled to native machine code (when used for building mobile apps), inspired by modern features of other programming languages (mainly Java, JavaScript, C#) and strongly typed. As already mentioned, Dart is a compiled language. That means, that your code isn’t executed as you write it, but instead, a compiler parses + transform it (to machine code).
2. what are the types?
These are some basic types — Dart has way more than these basic types though. You will learn way more about these (and all the other important) types throughout the course. At the moment, these are types you should keep in mind:
for example
a. String myName = ‘Max’ ( it holds all the text. you can use single or double quotes)
b. int age = 30; , double price = 9.99 ( it refers to the numbers , either it can be with decimal or only with integers.
c. object = person(person) (Generally, everything in Dart is an object — even an integer. But objects can also be more complex)
3. Variables and Functions
In your programs, you typically need to store some values. Not necessarily in a database or in a file but in memory. You might need to store some intermediate result, the input of a user before you process it or some information about your Flutter widget (e.g. “Should it currently be displayed on the screen?”). You store such information (= values) in so-called variables. Variables are data containers — they have names and store values of any type. For example: var myAge = 30; is a variable that stores an integer (int) of value 30.
The var keyword tells Dart that myAge is a variable. Alternatively to var, you could also use the type name — in addition to informing Dart about the variable, you would then also “inform Dart” about the type of data stored in the variable: int myAge = 30;
However, Dart has a feature called “type inference”. This means, that Dart is pretty smart about inferring types of values. If you created the variable with var, Dart is still able to infer that myAge is of type int because you initialize the variable (i.e. you assign a value right from the start) with an integer value. Type Example More Information String String myName = ‘Max’; Holds text. You can use single or double quotes — just be consistent once you made your choice. num, int, double int age = 30; double price = 9.99 num refers to “number” — there are two types of numbers in Dart: Integers (numbers without a decimal place) and doubles (numbers with decimal places) object Person = Person() Generally, everything in Dart is an object — even an integer. But objects can also be more complex, see below. Because of that built-in type inference, it’s considered a good practice to NOT explicitly define the type but instead use var when defining variables. Hence this snippet would be preferred: var myAge = 30; That changes if you create a variable without an initial value — then, you should inform Dart about which type of data you plan on saving in there: int myAge; myAge = 30;
Besides variables, another core feature of ANY programming language are “functions”. Functions allow you to “outsource” code into “re-usable code snippets”. Here’s an example: var price1 = 9.99; var price2 = 10.99; var total = price1 + price2; var numOfRounds1 = 10; var numOfRounds2 = 45; var totalRounds = numOfRounds1 + numOfRounds2; In this example, we have the same logic of adding two numbers in two different places of our code. Instead of repeating ourselves, it would be great to put that logic into a function that we can call whenever as often as we want. Here’s the changed snippet, using a function: num addNumbers(num n1, num n2) { // use num as a type because it should work with int and double return n1 + n2; } var price1 = 9.99; var price2 = 10.99; var total = addNumbers(price1, price2); var numOfRounds1 = 10; var numOfRounds2 = 45; var totalRounds = addNumbers(numOfRounds1, numOfRounds2); Of course, on first sight, this code now got longer and more complex. But the advantage is, that if you ever need to change your addition logic, you do it in one place => Inside of the function. You don’t have to edit multiple places in code just to change the + into a — for example (if you wanted to do that). Functions can take arguments (the data between the ( )) which are basically variables, scoped to the function. “Scoping” means that you can use the variables only inside of the block statement (= function body, the code between the { }) where you defined them.
what does “object-oriented mean?
What does “Object-oriented” mean? Dart is an object-oriented programming language — that means that every value in Dart is an object. Even a simple number. What are “objects” though? Objects are data structures — you find them in a lot of programming languages. In Dart, every value is an object, even primitive values like text (= String) or numbers (= Integers and Doubles). But you also have more complex built-in objects (e.g. Lists of data) and you can build your own objects. You often build your own objects if you want to express more complex relations between data or if you want to encapsulate certain functionality in “one building block”. Objects are created with the help of “Classes” because every object needs a blueprint (=> the class) based on which you can then create (“instantiate”) it. Here’s an example class definition: class Person { var name = ‘Max’; var age = 30; void greet() { print(‘Hi, I am ‘ + name + ‘ and I am ‘ + age.toString() + ‘ years old!’; } } In this example, we define a Person class which has two class-level variables (also called “instance fields” or “properties”) and one class-level function (also called “method”). As you can see, we also use types in classes — for both properties (variables) and methods (functions). You can also see, that inside of the greet method, we can access the class properties name and age without issues (age.toString() is used to covert the integer value to a string whilst outputting it in a longer string). The class only serves as a blueprint though! On its own, it does not give you an object! Instead, you can now create objects based on this class: class Person { var name = ‘Max’; var age = 30; void greet() { print(‘Hi, I am ‘ + name + ‘ and I am ‘ + age.toString() + ‘ years old!’; } } void main() { var myself = Person(); print(myself.name); // use the . to access class properties & methods } As a side note: The main function is a special function in Dart — it’s the function which Dart will execute first, when your app starts. Inside of main, we then create a new object based on Person by using Person(). This process is called “instantiating the class”, hence we create “an instance of Person”.