Object reference is not set to instance .

Question

1.00/5 (1 vote)

See more:

I got above error when my program runs. It gives error at SendKeys.SendWait method.
It gets proper input but didn't work. Actually in my scenario I want to send received data to activated window (i.e word , excel , notepad , or any application text box which is activated at that instance).
Help me please, Thanks

here is code,

C#

void sendkeytest(string input)
      {
           //static extern int SetForegroundWindow(IntPtr point);
          Process p = Process.GetCurrentProcess();

          IntPtr h = p.Handle;
          SetForegroundWindow(h);
          if (p.Responding)
          {
              foreach (char c in input)
              {
                  SendKeys.SendWait(c.ToString());
              }
          }
      }

if (res.StartsWith("*"))
{
   sendkeytest(res);

}

In above code "res" is string received from socket and i want to send this string to activated window i.e text editor opened at runtime.

Posted 28-Jul-15 19:40pm

Member 11543226

Updated 28-Jul-15 20:22pm

v2

Add a Solution

Comments

Sergey Alexandrovich Kryukov 29-Jul-15 2:16am

Why using SendKeys?
—SA

2 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

OriginalGriff · Answer 1 · 2015-07-28T19:57:00

We can't tell - because we can't run your app.
So start with the debugger, and look at exactly what is happening when you get the error.
SendKeys.SendWait is a static method - so it can't generate a null reference error on it's own. So res must be doing it.
Since res is a string (or the StartsWith method call would not compile) we can ignore the ToString call as it's already a string and the call is redundant.
So it must be the res.StartsWith itself that causes the problem - which means that res itself is null.

Now you have to find out why: and we can't do that for you!
Once you have confirmed that res is null, put a breakpoint at the top of the method, and step through to find out why.

Sergey Alexandrovich Kryukov · Answer 2 · 2015-07-28T20:18:00

If your observations are correct, res is null, which throws exception in "if" statement. Isn't it obvious?

You did not really show exact line 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

Object reference is not set to instance .

2 solutions

Solution 1

Solution 2

Add your solution here

Preview 0