Object reference not set to an instance of an object.

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1.00/5 (1 vote)

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Hi all,
I have a small doubt.
I have a following class in my .dbml file. it has one string properity strType,

C#

[global::System.Data.Linq.Mapping.TableAttribute(Name="dbo.tblWorkType")]
    public partial class tblWorkType : INotifyPropertyChanging, INotifyPropertyChanged
    {

        private static PropertyChangingEventArgs emptyChangingEventArgs = new PropertyChangingEventArgs(String.Empty);

        private int lngWorkTypeID;

        private string strType;

        private bool Duration;

}

when I create Object of this its string properity initilized with null.

And when I try string.IsNullOrEmpty(objWorkTypeToAdd.strType.Trim()) it gives me error that "Object reference not set to an instance of an object."

my class object has already initilized,,,,but when I am trying to check its properity then I can't.
Can any one please tell me why the string.IsNullOrEmpty() gives error.

See the screenshot for detail from below link.
http://picpaste.com/pics/5306819cdbbacf658c3a181e13eddcff.1416290747.jpg[^]

Thanks in advance

Posted 17-Nov-14 19:09pm

Devendra lodha

Updated 17-Nov-14 19:21pm

v3

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Comments

Sergey Alexandrovich Kryukov 18-Nov-14 1:12am

What code sample you are showing? This class is apparently incomplete; it's code is probably unrelated to the problem.
—SA

2 solutions

Solution 1

You did not show where the exception with the message "Object reference not set to an instance of an object" is thrown.

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

Posted 17-Nov-14 19:14pm

Sergey Alexandrovich Kryukov

Updated 17-Nov-14 19:15pm

v2

Comments

Devendra lodha 18-Nov-14 1:32am

The exception is thrown by string.IsNullOrEmpty() when I am trying to check Object's property "strType" as string.IsNullOrEmpty(objWorkTypeToAdd.strType.Trim())

Sergey Alexandrovich Kryukov 18-Nov-14 1:37am

No, it is not!
It is thrown before you call it, because either objWorkTypeToAdd or objWorkTypeToAdd.strType is null. Then you dereference null and get your exception. You need to interprer what debugger shown correctly. Your line is not one operation, but some 4 of them.
—SA

BillWoodruff 18-Nov-14 3:21am

Really valuable comments about debugging Sergey, but, in this case, the error is a very simple one caused by the use of 'Trim on an uninitialized (null) string. Because 'Trim is invoked inside the condition clause of an 'if statement, the debugger is going to highlight the entire line where the if/condition appears.

Sergey Alexandrovich Kryukov 18-Nov-14 9:02am

Sure, it is, but pay attention for the comment above: OP failed to see this reason even when the debugger pointed to this line with Trim(). Simple or not, the problem is really about the debugging... :-)
—SA

Manas Bhardwaj 18-Nov-14 6:53am

Nice +5!

Sergey Alexandrovich Kryukov 18-Nov-14 9:00am

Thank you, Manas.
—SA

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BillWoodruff · Accepted Answer · 2014-11-17T21:13:00

Solution 2

Your error is caused by trying to use 'Trim on an uninitialized (null) string.

Posted 17-Nov-14 21:13pm

BillWoodruff

Updated 17-Nov-14 21:14pm

v2

Comments

Manas Bhardwaj 18-Nov-14 6:53am

Agree +5!