IDisposable or not in custom classes

Following on from the recent thread about why HttpWebRequest doesn't
implement the IDisposable interface, I got to wondering whether people
make their custom classes inherit IDisposable or not as a general rule, or
only under certain circumstances...

Since it's an easy enough thing to do
(http://msdn2.microsoft.com/en-us/lib...sposable.aspx), is
there any good reason not to make every custom class IDisposable, the same
way as there's no good reason not to use exception handling in every
method...?

I can understand the rationale for implementing IDisposable for classes
which e.g. use unmanaged resources, or which open files and/or streams,
because the GC won't know about them, but what about for classes which use
/ reference only managed code? Would it be overkill to make those classes
IDisposable, and would it simply be enough to destroy references to them
by variables which have instantiated them to null...?

classes which e.g. use unmanaged resources, or which open files and/or
streams, because the GC won't know about them, but what about for
classes which use / reference only managed code? Would it be overkill
to make those classes IDisposable, and would it simply be enough to
destroy references to them by variables which have instantiated them
to null...?

Hi,
>
Following on from the recent thread about why HttpWebRequest doesn't
implement the IDisposable interface, I got to wondering whether people make
their custom classes inherit IDisposable or not as a general rule, or only
under certain circumstances...
>
Since it's an easy enough thing to do
(http://msdn2.microsoft.com/en-us/lib...sposable.aspx), is there
any good reason not to make every custom class IDisposable, the same way as
there's no good reason not to use exception handling in every method...?
>
I can understand the rationale for implementing IDisposable for classes
which e.g. use unmanaged resources, or which open files and/or streams,
because the GC won't know about them, but what about for classes which use /
reference only managed code? Would it be overkill to make those classes
IDisposable, and would it simply be enough to destroy references to them by
variables which have instantiated them to null...?
>
Interested to know your opinions...
>
Mark

IDisposable should be implemented if your class composites:
>
A. unmanaged resources
B. IDisposable types
>
If your class doesn't manage the lifetime of unmanaged or IDisposable
references then IDisposable isn't necessary. In all other circumstances,
IDisposable isn't necessary either.

Hi,
>
Following on from the recent thread about why HttpWebRequest doesn't
implement the IDisposable interface, I got to wondering whether people
make their custom classes inherit IDisposable or not as a general rule, or
only under certain circumstances...
>
Since it's an easy enough thing to do
(http://msdn2.microsoft.com/en-us/lib...sposable.aspx), is
there any good reason not to make every custom class IDisposable, the same
way as there's no good reason not to use exception handling in every
method...?
>
I can understand the rationale for implementing IDisposable for classes
which e.g. use unmanaged resources, or which open files and/or streams,
because the GC won't know about them, but what about for classes which use
/ reference only managed code? Would it be overkill to make those classes
IDisposable, and would it simply be enough to destroy references to them
by variables which have instantiated them to null...?
>
Interested to know your opinions...
>
Mark
>

If you have the class implementing the IDisposable interface then it must
have a Dispose() method since that is part of the interface.

Can you show the thread that you are referring to?

I don't know if it was pointed out, but there is no reason to implement
IDisposable on the request since the request doesn't do anything until it
is sent.

And yes, it is overkill to implement it on all the classes.

There are very specific guidelines in place for when to implement
IDisposable.

>"Mark R. Dawson" <MarkRDawson@discussions.microsoft.comwrote in message
>news:DF26A3D0-7CC0-4047-B5BC-BC3A707F8875@microsoft.com...
>>
>D'oh! I really could have found that out for myself...Apologies.
>
>I'm learning a lot of good practices here, though...
>
>OK, here's another one...
>
>Let's say you have a Database Abstraction Layer class called MyDAL which,
>for the sake of argument, has a static method called GetSqlDataReader which
>accepts a string of SQL as its only argument and returns an SqlDataReader
>object). Barring the obvious comments about using stored procedures to avoid
>SQL Injection, it might look something like this:
>
>public static SqlDataReader GetSqlDataReader(string strSQL)
>{
try
{
using (SqlConnection objSqlConn = new SqlConnection(<read connection
>string from config file>))
{
using (SqlCommand objSqlCommand = new SqlCommand(strSQL,
>objSqlConn))
{
objSqlCommand.Connection.Open();
return
>(objSqlCommand.ExecuteReader(CommandBehavior.Clos eConnection));
}
}
}
catch (SqlException ex)
{
throw ex;
}
catch(Exception)
{
throw;
}
>}
>
>You might use it something like this:
>
>using (SqlDataReader objDR = MyDAL.GetSqlDataReader("SELECT * FROM
>MyTable"))
>{
while (objDR.Read())
{
// do something
}
objDR.Close(); // is this necessary?
>}
>
>Since SqlDataReader is disposable, and it has been instantiated with the
>using (...) syntax, and the reader itself has been created with the
>ExecuteReader method of a SqlCommand object specifying the
>CommandBehavior.CloseConnection property), is the line "objDR.Close()"
>necessary...?
>

Close() is not necessary when using "using".

Also note that since your class is returning a connected Reader
instance you do not want to use "using" on the SqlConnection object
'cause you don't want to close the connection. That's why readers
have the CloseConnection behavior, you don't have to worry about
closing the connection 'cause the reader closes it automatically when
the reader itself is closed.

>
Are there? Are they available for download anywhere...?

"Nicholas Paldino [.NET/C# MVP]" <mvp@spam.guard.caspershouse.comwrote
in message news:%23T6DsguHHHA.4712@TK2MSFTNGP04.phx.gbl...
>
Nicholas,
>>
Its subject is "HttpWebRequest and IDisposable" and it was started by me
in this group on 10th December.
>>
It's actually not possible to implement it because it's not disposable,
much to everyone's surprise...
>>
Indeed.
>>
Are there? Are they available for download anywhere...?
>
Mark
>

>
".NET Framework Developer's Guide, Implementing Finalize and Dispose to
Clean Up Unmanaged Resources"
http://msdn2.microsoft.com/en-us/library/b1yfkh5e.aspx
>
".NET Framework Developer's Guide, Implementing a Dispose Method"
http://msdn2.microsoft.com/en-us/library/fs2xkftw.aspx
>
Check out the TOC on the left and you'll see a whole bunch of topics that
provide development guidelines for many other things.