Getx Flutter while updating value throwing null error

Question

Data Model

class DataModel {
  Book? book;
  DataModel({
     this.book,
  });
}

class Book {
  String author;
  Book({
    required this.author,
  });
}

Getx Controller

class BookController extends GetxController{
   var dataModel = DataModel().obs;
  updateAuthor(){
    dataModel.value.book!.author = "";
  }
}

While updating author Getx throwing " null checked used on a null value"

After changing the function to this

  updateAuthor(){
    dataModel.value.book?.author = "";
  }

It is not updating the value, making it null.

Also tried with update method unable to update the value with this type of data model.Class inside class.

I am just trying to update the author but unable to do it.

Answer 1

Here, I will explain what you did wrong,

First, you made an object of DataModel.

   var dataModel = DataModel().obs;

this dataModel have a book property which you marked it with a ? so you made it nullable.

so at this point this:

dataModel.value.book == null ; // true

you didn't assign a real Book instance to the book property, so it's null, so this line:

dataModel.value.book!.author = ""; // will throw an error

because dataModel.value.book is null.

what you need to assign a new Book() object to the book property like this, specifying the author property that Book()

  updateAuthor(){
  dataModel.value.book = Book(author: "");
  dataModel.refresh();
  }

now we have a real Book object assigned to book, this will fix the null error you got.