Dart

#Tip of the Day: “别认输，再加把劲，直到最后，超越自我； 不管相离多远，心都在一起，追逐着遥远的梦”

SDK

Use the stable version, otherwise there is some error in IntellijIDEA

Convention

Program entrance: main() method.

Naming convention: file name, use lowercase and underscore.

List and Map

List is similar as the array in JavaScript. And Map is like the array in PHP.

dynamic type

var or dynamic

~/ Divide, returning an integer result

int d = 20;
int e = 10;
print(d / e );

This will give us 2.0, which is a double.

However,

int d = 10;
int e = 3;
print(d ~/ e);

This will give us 3

We can include a variable inside a String with ${expression}

int aNumber = 5;
print('The number is $aNumber.');

result:

The number is 5.

Use “==” to compare Strings.

string.isEmpty will result a null pointer exception if this String is null.

Uninitialized variables have an initial value of null. Even variables with numeric types are initially null.

int lineCount;
assert(lineCount == null);

Important concepts

• Everything you can place in a variable is an object, and every object is an instance of a class.
• Dart is strongly typed. When you want to explicitly say that no type is expected, use the special type dynamic.
• 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.

??= Assignment operators; ?? if null

To assign only if the assigned-to variable is null, use the ??= operator.

// Assign value to b if b is null; otherwise, b stays the same b ??= value;

expression1 ?? expression2

String a;
String b = "Java";
String c = a ?? b;
print(c);

if a is null, then use b; otherwise use a.

For loop

var list = [1, 2, 3, 4, 5];

for (var i = 0; i < list.length; i++) {
  print(list[i]);
}

for (var item in list) {
  print(item);
}

Optional Parameters

void main(){
    printPerson("A", age: 20);
}

printPerson(String name, {int age, String gender}){
    print("name=$name,age=$age, gender=$gender");
}

If “[]” is used, then the parameter name like “age: “ can be omitted. It will be determined by positions.

void main(){
    printPerson("B", 20);
}

printPerson(String name, [int age, String gender]){
    print("name=$name,age=$age, gender=$gender");
}

Default parameter value

If a parameter’s value is not given, then use the default one.

printPerson(String name, [int age = 30, String gender = "male"]){
    print("name=$name,age=$age, gender=$gender");
}

Function closure

void main(){
    var func = a();
    func();
    func();
    func();
    func();
}

a(){
    int count = 0;
    
    printCount(){
        print(count++);
    }
    
    return printCount;
    
}