dart class 构造函数中的可选 Arguments

Question

why there is error while am trying to construct my constructor i want to have a named paramters but not required ones how i can fix this

class Task {
   int id;
   String title;
   String description;

  **Task({this.id , this.title , this.description}); // Giving me Errors here**

  Map<String , dynamic> toMap()
  {
    return {
      'id' : id,
      'title' : title,
      'description' : description,
    };
  }
  @override
  String toString() {
    return 'Task{id: $id, name: $title, age: $description}';
  }
}

Answer 1

If you don't want the arguments to be required , you have to allow them to be null by adding a question mark to their type, so Dart will know that they don't need to be initialized. Like this:

   int? id;
   String? title;
   String? description;

Another solution is to give them a default value in the constructor, but be careful to assign them values that won't conflict with the rest of your code:

Task({this.id=-1, this.title='Title' , this.description = 'Description'});

Choose the approach that suits you best: you can also use a mix of the two solutions, like making some properties nullable and giving a default value to the others.