Object Reference not set to an instance of object

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Hi,

When I write the following code in button am getting the error that 'object reference not set to an instance of object'.

C#

public Test t=new Test();
       private void button4_Click_1(object sender, EventArgs e)
       {
           nm = button4.Text;
           this.Hide();
         //  Test t = new Test();
           t.ShowDialog(this.Owner);
           this.Close();
       }

I don't know what updation need to be added to this code.

Posted 9-Sep-15 20:00pm

Member 10994712

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Sergey Alexandrovich Kryukov 10-Sep-15 2:20am

In what line?
Note that this is not a self-sufficient code sample. You cannot ask such questions without showing at least the declarations of all variables and members you are showing. Can you be just logical?
—SA

2 solutions

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Sergey Alexandrovich Kryukov · Accepted Answer · 2015-09-09T20:23:00

Please see my comment to the question. 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

DamithSL · Accepted Answer · 2015-09-09T20:18:00

Solution 1

One of your object references is NULL. You'll see this when you try and access the property or method of a NULL'd object. debug and see which object is null at run time.
According to your code, object "t" may be null at the time you call ShowDialog but I can't exactly say which object is null with the given details. please update the question with full error stack trace and also try to debug and understand the which code blocks execute and how the given object is null etc..

Posted 9-Sep-15 20:18pm

DamithSL

Updated 9-Sep-15 20:19pm

v2

Comments

CPallini 10-Sep-15 2:30am

5.

DamithSL 10-Sep-15 3:07am

Thank You.

Member 10994712 10-Sep-15 5:50am

I debugged the code and it shows error in this line
t.ShowDialog(this.Owner);

here this.Owner is null.

Member 10994712 11-Sep-15 0:14am

How can I solve this error?