Urgent: DBNull error - 'System.InvalidCastException'

Posted by Supernova122 under VB.NET on 12/10/2013 | Points: 10 | Views : 1455 | Status : [Member] | Replies : 6
Using Visual Studio 2008 and generating .net 2.0 framework with VB.net for a web application.

I encountered a very strange problem currently. After I build a solution and click a link in a web page, I got an error message as following. The same thing happened when I tried to run in debug mode.

************* Error ************************************************************
"An exception of type 'System.InvalidCastException' occurred in Microsoft.VisualBasic.dll but was not handled in user code"

"Additional information: Operator '=' is not defined for type 'DBNull' and string "". "
***********************************************************************************

The problem part is simply as below in a vb file. The value of dataview(0)(“name”) is NULL and my_name is a variable string. The strange is thing I didn’t change any code in this vb file. This vb file was built previously and used for a long time ago without any problem. It just suddenly happened today. I have this syntax all over the program without causing any problem. I have tried to restore the whole solution back to original but still have the problem. Can anyone please advise why all the sudden and how to fix? Thanks.

“If dataview(0)(“name”) = my_name then …”




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Posted by: Bandi on: 12/10/2013 [Member] [MVP] Platinum | Points: 25
Posted by: Bandi on: 12/10/2013 [Member] [MVP] Platinum | Points: 25

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try this ?

If Not IsDbNull(dataview(0)(“name”)) AND dataview(0)(“name”) = my_name then 


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Posted by: vishalneeraj-24503 on: 12/10/2013 [Member] [MVP] Platinum | Points: 25

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Check
If Not IsDbNull(dataview(0)(“name”)) AndAlso Convert.Tostring(dataview(0)(“name”))= my_name Then


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Posted by: Supernova122 on: 12/10/2013 [Member] Starter | Points: 25

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Thanks for the advice. Actually, I have the problem syntax all over the program and they don't have problem before. If I change it one by one, that will take forever. Could this has something to do with Visual Studio 2008 or microsoft.visualbasic.dll library? I am thinking on what is the source of the problem, what could be the change on the environment as I haven't touched the code. Please help. Thanks a lot.

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Posted by: vishalneeraj-24503 on: 12/10/2013 [Member] [MVP] Platinum | Points: 25

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Hi,please enable
Option Explicit On and Option Strict ON at the Top of the page in vb.net

it will check syntax and type conversion.

please include this. and check it.

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Posted by: Supernova122 on: 12/10/2013 [Member] Starter | Points: 25

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Thanks. I will try that.

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