One minute to familiarize yourself with the meaning of all fluent question marks

The ?? Double question mark operator “ If empty ”. Take the following expression as an example .
String a = b ?? ‘hello’;

It means a be equal to b, But if b by null, be a be equal to ’hello’.
2.
Another related operator is ??=. for example ：
b ??= ‘hello’;

This means that if b by null, Set it to hello. otherwise , Do not change .
3.

String? name;
Adding a question mark allows the static check to pass , Represents a nullable type ,String? Is a nullable type String,
Type followed by operator ? Indicates that the current variable can be null.
4.
Use （.） To access an instance variable or method of an object ：
Use ?. Instead of . You can avoid that because the expression on the left is null And the resulting problems