error while converting decimal to string

Question

1.44/5 (2 votes)

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C#

decimal a = 0;
             for (Int32 i = 0 ; i< this.GridView1.Rows.Count; i++)
             {

                 a = a+ Convert.ToDecimal(((Label)GridView1.Rows[i].FindControl("lbl_price")).Text.ToString());

             }
             lbl_total.Text =  Convert.ToString(a);

this is my code and in the last line when i am assign the value of a into label m getting error?
error is this...

C#

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error: 


Line 104:                
Line 105:             }
Line 106:             lbl_total.Text =  Convert.ToString(a);
Line 107:         
Line 108:        }

Posted 24-Sep-13 18:35pm

Omprakash Kukana

Updated 24-Sep-13 18:36pm

v2

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PIEBALDconsult 25-Sep-13 0:54am

Rule 1: Don't use the Convert class; it's needless. Just use the appropriate Parse or TryParse method on the type you want; they're way better and Convert simply calls them anyway, so all you've done is add a call to the stack for no reason.

Same with ToString, just call a.ToString(), don't even think about using Convert.

Also, try not to call ToString on something that's already a string -- e.g. .Text.ToString()

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Sergey Alexandrovich Kryukov · Accepted Answer · 2013-09-24T18:44:00

I'm not sure if you pointed out correct line where the exception was thrown, because it would mean that, by some reason, lbl_total is null. Anyway, check it up with the debugger.

In case your information on this exception is inaccurate, and in all such cases in general, it's much more important that you master the technique of locating and fixing such problems by yourself. 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

Omprakash Kukana · Accepted Answer · 2013-09-25T01:25:00

Solution 2

C#

decimal a = 0;
           for (Int32 i = 0; i < this.GridView1.Rows.Count; i++)
           {

               a = a + Convert.ToDecimal(((Label)GridView1.Rows[i].FindControl("label3")).Text.ToString());

           }
           lbl_total.Text = Convert.ToString(a);

Posted 25-Sep-13 1:25am

Omprakash Kukana

Comments

PIEBALDconsult 25-Sep-13 9:41am

How is that different from the original?