My sample below which uses try...finally does handle the case properly if there is an exception thrown in either the command constructor or the connection creation.
For example if the connection is properly constructed with no exceptions then cn is not null and cn.Close() will be closed no matter how the routine exits (by return or by exception). If an exception occurs during connection creation then cn is null and cn.Close() will not be called. The main advantage to using nested using statements is that the using statement allows putting your construction and cleanup code in one place (at the top of the using block). There is a downside though. Each using statement creates a new try...finally construct. Look through ILDASM and you will see a try...finally block for every nested using statement. While try...finally overhead might be minimal, it still requires more overhead than hand coding the try...finally block. It would be nice if the using statement allowed initialization of multiple types at once! *sigh* -- Peter > Kirk Jackson spake: > > The reason 'using' is useful, is that you don't need to worry > about an exception being thrown from your first dispose call (as > if there is an exception, you'd still want to call cn.Close) > > Kirk > > -----Original Message----- > From: Peter Stephens [mailto:[EMAIL PROTECTED]] > Sent: Thursday, 2 May 2002 8:03 p.m. > To: [EMAIL PROTECTED] > Subject: Re: [DOTNET] From C# to VB.NET > > > Thank you Mattias, > > I had never considered that multiple using statements before the > code block were valid. I certainly haven't seen it used like this > before. Your second technique is also interesting except that it > requires the overhead of the cast. > > My typical pattern is: > > SqlConnection cn = null; > SqlCommand cmd = null; > try > { > cn = new SqlConnection(...); > cmd = cn.CreateCommand(); > > // Do something > } > finally > { > if(cmd != null) cmd.Dispose(); > if(cn != null) cn.Close(); > } > > This keeps everything strongly typed from the start. Still your > first technique is intriguing in that it also eliminates the > chance of forgetting the cleanup code in the finally block... > > -- > Peter > > > > Mattias Sjögren spake: > > > > Peter, > > > > >I will often use the try ... finally pattern in C# if there is > > more than one > > >type of resource to clean up. The using statement only supports > > one type at > > >a time. > > > > Yes, but you can easily nest them > > > > using ( DisposableType1 d1 = new DisposableType1() ) > > using ( DisposableType2 d2 = new DisposableType2() ) > > using ( DisposableType3 d3 = new DisposableType3() ) { > > // ... > > } > > > > or > > > > using ( IDisposable d1 = new DisposableType1(), d2 = new > > DisposableType2() ) { > > DisposableType1 dt1 = d1 as DisposableType1; > > DisposableType2 dt2 = d2 as DisposableType2; > > // ... > > } > > > > > > Mattias > > You can read messages from the DOTNET archive, unsubscribe from > DOTNET, or subscribe to other DevelopMentor lists at http://discuss.develop.com. You can read messages from the DOTNET archive, unsubscribe from DOTNET, or subscribe to other DevelopMentor lists at http://discuss.develop.com. You can read messages from the DOTNET archive, unsubscribe from DOTNET, or subscribe to other DevelopMentor lists at http://discuss.develop.com.
