non reference exception was unhandeled by your code

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public static int Room_Capacity(int i)
{

SqlConnection conn = ConnectingDatabase.GetConnection();
string com= "SELECT Room_Capacity FROM Room where Room_ID =" + i;
SqlCommand commnd = new SqlCommand(com, conn);

int RoomCapacity = (int)commnd.ExecuteScalar();

conn.Close();

return RoomCapacity;

}
he tell me that error///non reference exception was unhandeled by your code

any answer please >>>i know that i am reference to null but how to solve that

Posted 2-May-13 12:11pm

mahmoud.abdallah

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Sergey Alexandrovich Kryukov 2-May-13 19:09pm

I'm sure you did not provide us with the real exception message, forget about other exception information. You should never type any essential messages or code, to avoid mistakes. Copy and paste.
—SA

2 solutions

Solution 1

If you're talking about the message "Object reference not set to an instance of an object", it means that you're trying to get/set a property or call a method on null.

Look at the line that threw the exception. Then trace the code back to where you should have gotten an object instance and see what's wrong.

With the code sniuppet you posted, it's impossible for anyone to tell you exactly what happened and what to do about it. You haven't shown which line the error occured.

Posted 2-May-13 12:26pm

Dave Kreskowiak

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mahmoud.abdallah 2-May-13 18:52pm

int RoomCapacity = (int)commnd.ExecuteScalar() the error is on that line

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-05-02T13:11:00

In your case, commnd was null. Was it so hard to check it up under the debugger?

Not to worry. This is one of the very easiest cases to detect and fix. It simply means that some member/variable of some reference type is dereferenced by using and of its instance (non-static) members, which requires this member/variable to be non-null, but in fact it appears to be null. Simply execute it under debugger, it will stop the execution where the exception is thrown. Put a break point on that line, restart the application and come to this point again. Evaluate all references involved in next line and see which one is null while it needs to be not null. After you figure this out, fix the code: either make sure the member/variable is properly initialized to a non-null reference, or check it for null and, in case of null, do something else.

Please see also: want to display next record on button click. but got an error in if condition of next record function "object reference not set to an instance of an object"[^].

Sometimes, you cannot do it under debugger, by one or another reason. One really nasty case is when the problem is only manifested if software is built when debug information is not available. In this case, you have to use the harder way. First, you need to make sure that you never block propagation of exceptions by handling them silently (this is a crime of developers against themselves, yet very usual). The you need to catch absolutely all exceptions on the very top stack frame of each thread. You can do it if you handle the exceptions of the type System.Exception. In the handler, you need to log all the exception information, especially the System.Exception.StackTrace:
http://msdn.microsoft.com/en-us/library/system.exception.aspx[^],
http://msdn.microsoft.com/en-us/library/system.exception.stacktrace.aspx[^].

The stack trace is just a string showing the full path of exception propagation from the throw statement to the handler. By reading it, you can always find ends. For logging, it's the best (in most cases) to use the class System.Diagnostics.EventLog:
http://msdn.microsoft.com/en-us/library/system.diagnostics.eventlog.aspx[^].

Good luck,

—SA