VB.NET - How do I assign an object to an object instance (better description inside)

Question

I have an object instance which I access with the ME as it accesses the instantiated object. I have a method that gets a collection of these objects and I wish to assign the first one to the instantiated object.

This is some of the code

Dim Books As New BookCollection(True)
Books.ListByThemeFeatured(ThemeID, 1) ' Fills the collection

If Books.Count > 0 Then
   Me = Books(0) ' Should set the first item to the current object
End If

Is this possible?

EDIT: Me refers to the class that was instantiated. In this case it is a BookEntity Class. THis method would have been called using the following code

 Dim Book As New BookEntity
 Book.FeaturedBook() ' Should fill the book entity with a featured book

Answer 1

You can't. What you're looking for is a static (shared in VB) method:

Dim Book as BookEntity
Book = BookEntity.FeaturedBook()

Answer 2

It seems impossible since you try to replace an object instance which you do not have the handle of. One choice may be replacing all members of your current Book instance with the values of the Books(0) like:

Me.ConstructMeFrom(Books(0))

Where ConstructMeFrom replaces all of a Book's fields:

Sub ConstructMeFrom(Book newBook)
    Me.Title = newBook.Title
    Me.PageCount = newBook.PageCount
    'etc
End Sub

Or you may design some method to modify the value of the handle that holds your instance. For e.g. you may use a delegate which replaces an instance itself with another instance. I am not familiar with vb syntax but here is how it would be done in c#:

public class Book
{
    public delegate void Replacer(Book book);

    public void ReplaceMe(Replacer replacer, Book newBook)
    {
        replacer(newBook);
    }

    public int PageCount;
}

static void Main(string[] args)
{
    Book b1 = new Book() { PageCount = 3 };
    Book b2 = new Book() { PageCount = 5 };
    b1.ReplaceMe(book => b1 = book, b2);
    Console.WriteLine(b1.PageCount); // Output is 5.
}

Update:

C# example with your updated example:

FeaturedBook(Replacer replacer)
{
    Book featuredBook = FindTheFeaturedBookFromSomeList();
    replacer(featuredBook);
}

Now do this:

BookEntity Book;
Book = BookEntity.FeaturedBook(delegate(BookEntity b) { Book = b; });

Answer 3

Either use a sub

public sub FeaturedBooks() 
    dim FB as Book = GetFeaturedBook() 
    CopyToMe(FB) 
end sub

private shared sub CopyToMe(Abook as book)
    Me.Bookname = aBook.BookName
     etc
end sub

or have a shared function, such that you write:

Dim Book as BookEntity = BookEntity.FeaturedBook()


Class BookEntity

Public shared function FeaturedBook() as BookEntity
    Dim NewBook as BookEntity
    Get the featured book into here...

    return NewBook
end function

end class

Answer 4

I am sorry but something "smells bad" about that code... why should you ever need to replace the current BookEntity object? Your code looks to be doing some things which should be outside the scope of a BookEntity.

I think instead, you should have a class like BookDisplayer which has a CurrentBook property that handles the logic necessary to display a new book. Assuming that is what you are trying to accomplish, of course.

EDIT:

It seems like the following code sample:

Book.FeaturedBook() ' Should fill the book entity with a featured book

Should look like this, with the FeaturedBook logic living in the BookCollection class instead:

Book = Books.GetFeaturedBook()
' NOW perform display logic