Dart language operator? and! usage of

1. Basic use

1. The ? operator follows the type, indicating that the current variable can be null.

int a = null; //这句代码在有空安全时，编译会提示错误

What if you want to assign null to a variable? Only need to type

Add operator after? That's it, eg:

int? a = null;

At the same time, when we use a variable or method of a nullable object, we need to use it ？. , but not ., eg:

2. The ! operator follows the type.

The operator ！requires the developer to ensure that the variable is not null, otherwise an exception will be thrown. eg:

here _socket will not be empty, so you can use it with confidence!.