Passing an Object by Ref

[Guest]

I have a few objects that I've created, Contact, Address, AddressCollection
(inherits from CollectionBase), dtaContact, and dtaAddress. One of the
properties of the Contact object (Contact.Addresses) is a Type of
AddressCollection. When I want to add a new contact to my database I create a
new Address object for each address and a new AddressCollection object. I
then populate the Address objects and add them to the AddressCollection
(InnerList.Add(address)). Next I populate the Contact object properties
including the AddressCollection. Now I want to pass the Contact object by Ref
to the dtaContact.Insert() method so that I can use the output parameter of
my SP to populate the ContactID property and have that value reflected in my
contact object. This functionality works just fine. However within my
dtaContact.Insert() method I want to loop through the AddressCollection and
pass each Address object by Ref to the dtaAddress.Insert method. When I do
this I get the following error when I try to Rebuild...

error CS1605: Cannot pass 'contactAddress' as a ref or out argument because
it is read-only

Can anyone provide some insight as to why this may be happening?

Thanks,

Mike G.

 

[Scott M.]

It appears that you have a property called: contactAddress that is marked
as ReadOnly.

 

[Guest]

Thanks for the fast reply Scott. The contactAddress is not marked ReadOnly,
here is the section where it is created...

dtaContactAddress contactAddressData = new dtaContactAddress();
foreach (ContactAddress contactAddress in contact.AddressCollection)
{
contactAddress.ContactId = contactID;
contactAddressData.Insert(ref contactAddress);
}

Could it be that objects in a collection are implicitly ReadOnly?

- Mike G.

 

[Jon Skeet [C# MVP]]

Thanks for the fast reply Scott. The contactAddress is not marked ReadOnly,
here is the section where it is created...

dtaContactAddress contactAddressData = new dtaContactAddress();
foreach (ContactAddress contactAddress in contact.AddressCollection)
{
contactAddress.ContactId = contactID;
contactAddressData.Insert(ref contactAddress);
}

Could it be that objects in a collection are implicitly ReadOnly?

Objects themselves aren't readonly. However, the *variable*
contactAddress is readonly - the variable used in a foreach is always
implicitly readonly.

It doesn't look to me like you need to pass contactAddress by reference
though - that would just allow Insert to change the value of
contactAddress, which itself is a reference.

I *suspect* you're a bit confused about reference types vs value types
and parameter passing.
See http://www.pobox.com/~skeet/csharp/parameters.html

 

[Guest]

Thank you Jon, I didn't realize that the variable used in a foreach is always
implicitly readonly.

I don't believe that I'm confused by reference and value types. For each
Address object in my collection, when the data from an Address object is
inserted into the database an AddressID will be returned in an output
parameter. I want to populate the AddressID property of the Address object
with that ID.

Thank you very much for your help.

~ Mike G.

 

[Patrice]

This is not a problem. Even objects passed byval are updatable (you just
allows to update or not *this* pointer).

Patrice

 

[Jon Skeet [C# MVP]]

Thank you Jon, I didn't realize that the variable used in a foreach is always
implicitly readonly.

I don't believe that I'm confused by reference and value types. For each
Address object in my collection, when the data from an Address object is
inserted into the database an AddressID will be returned in an output
parameter. I want to populate the AddressID property of the Address object
with that ID.

And you don't need to pass anything by reference in order to do that.
Pass the reference to an Address object (passing that reference by
value) and update it in your method.

Put it this way: passing a variable by reference when you then make no
use of the potentially changed value of the variable should always
raise alarm bells - there's no (semantic) point in passing the variable
by reference in that case.

See the article I referred to in my last post.