无法将类型&#39;void&#39;隐式转换为System.Action <int>

Question

I am trying to create .net standard delegate, Action with the input parameter int . But I am getting

Cannot implicitly convert type 'void' to System.Action.

I learned that same return type methods can be added to multicast delegates. Below is my code. What is the wrong with this code? I don't see a compilation error if I write lambda expression.

static void Main(string[] args)
{
    Action<int> AddBook = AddBookwithId(15); // Here is the error
    AddBook += x => Console.WriteLine("Added book with :{0}" , x ); // No compile error here
    AddBook += AddBookwithISBN(56434);// of course, the same error here too.
}

public static void AddBookwithId(int y)
{
    Console.WriteLine( "Added Book to the shelf with the ID : {0} ", y ); 
}

public static void AddBookwithISBN(int y)
{
    Console.WriteLine("Added Book to the shelf  with the ISBN: {0} ", y + 2);
}

Answer 1

The code below compiles... The integer is expected to be passed when the Action is invoked.

       Action<int> AddBook = AddBookwithId; // Here is the error
       AddBook += x => Console.WriteLine("Added book with :{0}", x); // No compile error here
       AddBook += AddBookwithISBN;// of course, the same error here too.

Answer 2

    delegate void AddBook(int y);

    static void Main()
    {

        AddBook addBook;
        bool IsISBN = false;

        if (IsISBN)
        {
            addBook = AddBookwithISBN;
        }
        else
        {
            addBook = AddBookwithId;
        }
        addBook += x => Console.WriteLine("Added book with :{0}", x);
    }
    public static void AddBookwithId(int y)
    {
        Console.WriteLine("Added Book to the shelf with the ID : {0} ", y);

    }

    public static void AddBookwithISBN(int y)
    {
        Console.WriteLine("Added Book to the shelf  with the ISBN: {0} ", y + 2);
    }

Answer 3

Why not to use Lambda expressions ? In fact, you have already used it in this line of code:

AddBook += x => Console.WriteLine("Added book with :{0}" , x ); // No compile error here

This will result in:

Action<int> AddBook = (x) => AddBookwithId(x); // Here is the error
AddBook += (x) => Console.WriteLine("Added book with :{0}" , x ); // No compile error here
AddBook += (x) => AddBookwithISBN(x);// of course, the same error here too.