如果变量不是 Dart 中的一行代码中的 null，如何有条件地执行代码？

Question

In Dart, how do we do an operation only if a variable is NOT null... and accomplish that in one line?

Example:

void main() {
  
  int? i; // pretend we don't know if it's null or not
  
  // the laborious way:
  if (i == null) {
    print("the variable is null");
  }
  
  // the one-line way:
  i ?? print("the variable is null");
  
  // the laborious way:
  if (i != null) {
    print("the variable is not null");
  }
  
  // the one-line way:
   
  // i <what opertaor goes here?> print("the variable is null")
  
}

Answer 1

Actually, if you remove body params'{}' it is single line.

 if (i == null) print("if (i == null), the variable is not null");

Also you can do something with ternary. but seems having extra null.

i == null ? print("i==null, the variable is not null") : null;

---

You can use this extension, you can return bool based on your need.

extension NullChecker<T> on T? {
  get isNull => print("This variable is ${this != null ? "not" : ""} null");
}

And use,

void main() {
  int? i = 4, j;
  i.isNull; //This variable is not null
  j.isNull; //This variable is  null
}