Object reference not set to an instance of an object.

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Hi, I am trying to access a MS Access database using Windows form. I added my connection string in App.congig file.

XML

 <?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
 
    <clear/>
    <add name="Constr" providerName="System.Data.OleDb" 
         connectionString="Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\XXXX\\Documents\\YYYYY.accdb; Persist Security Info=False;"/>
    
  </connectionStrings>
</configuration>

Code I added in my code to read this is

string connectionstring = ConfigurationManager.ConnectionStrings["Constr"].ConnectionString;

but I am getting following error on this line.

System.NullReferenceException was unhandled
Message=Object reference not set to an instance of an object.
Source=LoadTrackingTool.

I am not getting why I am getting this error. Can anyone please help me out in this. I am new in this functionality.

Thnx,
Aduu

Posted 11-Nov-12 14:02pm

Aduu

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Sergey Alexandrovich Kryukov · Answer 1 · 2012-11-11T17:02:00

This kind of exceptions is one of the easiest to debug and fix. If happens, when you try to dereference some variable/member of some reference type by using one of the instance member of this type. Any such operations requires the reference to be non-null; If it's a null, this exception is thrown. In your case, ConfigurationManager.ConnectionStrings["Constr"] should be null. Check up the index value "Constr" — it could be misspelled, or a connection string under this name is not found in the configuration.

Please see:
http://msdn.microsoft.com/en-us/library/system.configuration.configurationmanager.connectionstrings.aspx[^],
http://msdn.microsoft.com/en-us/library/c6t3b6f3.aspx[^].

—SA

Abhinav S · Answer 2 · 2012-11-11T18:37:00

Solution 2

Try to debug this error. In most likelihood, you are trying to access a property of an object that is null.

Posted 11-Nov-12 18:37pm

Abhinav S