Creating and changing existent Methods for Dart classes - dart

Question

I'm trying to program with Dart on Visual Studio Code and need to understand the Syntax of Dart a bit more to be able to code what is needed.
These are the classes I have coded:
Book (defines book title, isbn, price and availability)
class Book {
// properties
late String _title;
late int _isbn;
late double _price;
bool _isAvailable;
....
}
BookCatalog (imports prior class and defines current list of books + methods to add new books)
class BookCatalog{
// no arrays, everything is a list
List<Book> _books = [];
...
}
Main (imports prior classes and executes wanted input)
What I want to change:
improve addBook Method within BookCatalog Class, to not add a new Book, if it has the same ISBN as a already existing one, which it currently does. (Potentially give out message stating 'false' if user tries to add Book with same ISBN)
// adds a book to the store
void addBook(book) {
_books.add(book);
}
improve printBookCatalog Method within BookCatalog Class, to only print available Books and not all Books added to the Store.
// Print books contained in the catalog
void printBookCatalog() {
print("List of Books:");
for (var book in _books) {
print(book);
}
}
improve getBook Method within BookCatalog Class, to actually get the book by its ID, as it's not working right now.
// Get a book by id
Book getBook(int place) => _books[place];
improve calculateAvgPrice Method within BookCatalog Class, to calculate the average price of Books, it's not working correctly as of now
// NEW, calculates average price of books
Book calculateAvgPrice(double price) {
for(var book in _books) {
sum += book.Price;
}
return sum / _books.length;
}
create a new Method within BookCatalog Class to delete Books from the Catalog
answer could be, but I'm not sure :
// deletes book from the catalog
void deleteBook(book) {
_books.remove(book);
}
Any help, explanations, examples or external sources to read up on Dart would be appreciated!
(Especially examples for my specific cases)

Answer 1

I suggest going through Dart Language Tour first.
(Side note: ISBN has leading zero and hyphen, so it's better to use a String for it instead of int)
In your BookCatalog class, you could use a Map instead of a List:
class BookCatalog {
Map<String, Book> _books = {}; // Map from ISBN to Book
// ...
}
Here I'm assuming that both classes are in the same file, otherwise accessing private members wouldn't work, so you'd have to have public getters available.
/// Adds a book to the store only if the ISBN does NOT exist.
bool addBook(Book book) {
if (_books.containsKey(book._isbn)) {
return false;
}
_books[book._isbn] = book;
return true;
}
Missing the if conditional.
void printBookCatalog() {
print("List of Books:");
for (final book in _books.values) {
if (book._isAvailable) {
print(book);
}
}
}
Assuming that by id you mean, its ISBN. It returns a nullable Book? because the isbn might not exist in the catalog.
// Get a book by id
Book? getBook(String isbn) => _books[isbn];
The function has a return type of double not a Book as it's the average price. You also don't need to provide any argument to this function. And you need to define the sum variable first before using it!
double calculateAvgPrice() {
var sum = 0.0;
for (final book in _books.values) {
sum += book._price;
}
return sum / _books.length;
}
Assuming that you want to remove books by their ISBN:
bool removeBook(String isbn) {
return _books.remove(isbn) != null;
}