Tim Abell - Professional Profile

Tim Abell11-Jan-06 5:53

11-Jan-06 5:53

Implement IDisposeable if you use "expensive" resources eg database connections.
I wrote this to help me understand how dispose is used and how it affects execution.

It's a basic console app (for .NET 2.0) and can be compiled with csc.exe

Here's the code:

using System;
public class hellodispose
{
    public static void Main()
    {
        Console.WriteLine();
        Console.WriteLine("test with dispose");
        Console.WriteLine("=================");
        Test(true);
        Console.WriteLine("====================");     
        Console.WriteLine();
        Console.WriteLine("test without dispose");
        Console.WriteLine("====================");
        Test(false);
        Console.WriteLine("====================");
    }

    private static void Test(bool rundispose)
    {
        Console.WriteLine("main()");
        Console.WriteLine("create dt:");
        disposetest dt = new disposetest(rundispose?1:0);
        Console.WriteLine("optionally call dispose:");
        if (rundispose) dt.Dispose();
        Console.WriteLine("end");
    }

    public class disposetest : IDisposable
    {
        private int _instance;
        public disposetest(int instance)
        {
            _instance = instance;
            Console.WriteLine("disposetest({0})", _instance);
        }
        ~disposetest()
        {
            Console.WriteLine("~disposetest({0})", _instance);
            Console.WriteLine("- force dispose: ({0})", _instance);
            Dispose();
        }

        public void Dispose()
        {
            Console.WriteLine("Dispose() ({0})", _instance);
           GC.SuppressFinalize(this); //try commenting this out - note dispose is called in the destructor even id it was called by the owner code.
        }
    }
}

And here's the output:

test with dispose
=================
main()
create dt:
disposetest(1)
optionally call dispose:
Dispose() (1)
end
====================

test without dispose
====================
main()
create dt:
disposetest(0)
optionally call dispose:
end
====================
~disposetest(0)
- force dispose: (0)
Dispose() (0)

and with the GC.SuppressFinalize(this) statement removed:

test with dispose
=================
main()
create dt:
disposetest(1)
optionally call dispose:
Dispose() (1)
end
====================

test without dispose
====================
main()
create dt:
disposetest(0)
optionally call dispose:
end
====================
~disposetest(0)
- force dispose: (0)
Dispose() (0)
~disposetest(1)
- force dispose: (1)
Dispose() (1)

The upshot of this as far as I'm concerned is:
- The IDisposable interface makes it clear the class uses expensive resources.
- Dispose() allows the consumer of a class to release the expensive resources immediately.
- The destructor should release the expensive resources, but only if they have not already been released, and using the GC.SuppressFinalize routine allows dispose to prevent the destructor from re-running the Dispose() routine.

Note that garbage collection is a separate thread, which is why the destructors fire outside the main routine.

References:

Programming for Garbage Collection
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconProgrammingEssentialsForGarbageCollection.asp

Implementing a Dispose Method
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpconimplementingdisposemethod.asp?frame=true&hidetoc=true

IDisposable Interface
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfsystemidisposableclasstopic.asp

IDisposable.Dispose Method
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpref/html/frlrfSystemIDisposableClassDisposeTopic.asp?frame=true&hidetoc=true

The IDisposable design pattern considered harmful
http://www.vbinfozine.com/a_disposable.shtml

Fundamentals of IDisposable (and some best practices)
http://www.codeproject.com/dotnet/ForDotNetBeginner.asp

Changing the title of MasterPage from the code of a templated page.

Tim Abell11-Jan-06 3:36

Tim Abell

11-Jan-06 3:36

Really damn simple when you know how.

From the (C#) code of the contained page:

<br />
Master.Page.Header.Title = "new page title";<br />

Handling "A potentially dangerous Request.Form value was detected"

Tim Abell9-Nov-05 5:07

Tim Abell

9-Nov-05 5:07

If you want an html editing form in asp.net, you get

Server Error in '/emapsite/intranet' Application.<br />
A potentially dangerous Request.Form value was detected from the client (txtContent="<h1>My new page...").

when a textbox containing "<" is encountered in a form submission.

The quick fix is to add validateRequest="false" to the page directive in your aspx file. Voila no errors.
No protection against script injection either, but if you're writing this then your probably writing a log in only admin page anyway.

---
This post was for my benefit. Let me know if it helps you and I might post more!

visual studio dataset xml / insert with autoincrement

Tim Abell10-Aug-05 6:03

Tim Abell

10-Aug-05 6:03

Here's something that flummoxed me for a while.

I'd created a dataset (with xml schema) using the visual studio 2002 designer and a dataadapter by hand. My main table was a normal table with an auto increment non-nullable int for a primary key. I created a record and poulated the values. When I tried to add the record to the dataset's datatable I received a message informing me I couldn't as the primary key was null.

Much scratching of head and googling later I found I needed to change the field definition of the primary key field from
<xs:element name="Record_ID" type="xs:int" minOccurs="0" />
to
<xs:element name="Record_ID" type="xs:int" minOccurs="0" msdata:ReadOnly="true" msdata:AutoIncrement="true" />

It occurs to me that last time I did something similar I'd pointed visual studio at sql server and told it to build the xml for me. This time I couldn't because visual studio can't (afaik) look into mysql.

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

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