NullReferenceException: "Object reference not set to an instance of an object" when user clicks a button

Question

I have deployed my software to a few users around the world, and today one of them told me he got this error. I've never seen it when running the software on my own machine, and I've not gotten any other reports of it.

When the user clicks a standard button, he gets the following error text:

System.NullReferenceException: Object reference not set to an instance of an object.
at x.MainForm.btnCreateOutput_Click(Object sender, EventArgs e)
at System.Windows.Forms.Control.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnClick(EventArgs e)
at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
at System.Windows.Forms.Control.WndProc(Message& m)
at System.Windows.Forms.ButtonBase.WndProc(Message& m)
at System.Windows.Forms.Button.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

I'm not really sure what to make of this message.

In btnCreateOutput_Click I just do some string work, I don't use the parameters of the function for anything.

There are a lot of similar functions in the software, and the error only happens with this button apparently.

Solution 1

Problem exists inside btnCreateOutput_Click, to see which line is responsible for exception you could attach .pdb's to installer, and you will get detailed information what file/line in your source is invalid.

Solution 2

First of all catch the exception and get the specific error....

it might be because of connection string getting wrong and the connection object is not initialized (well if at all your application uses one...)..

Comments

[Sergey Kalinichenko]

Please post btnCreateOutput_Click code.

[gosr]

If I do this, will I get more exception text from the user? I mean now it only says which method is "failing". And to be honest, I think I've already enabled this by the looks of it.

[cichy]

Problem exists inside click method. To see where exactly you could give user .pdb and you should get file/line wich is failing. You could also log to his computer via remote desktop for 3 min, to check yourself by using ie. Ammyy Admin ;)

[Tigran]

@cichy: as I wrote I assume in my post that OP has no any "easy" access to the client machine or client time to make him to test it.

[cichy]

@Tigran i have read it. Eventualy he needs to take some of his clients time to find error, ie. by reinstalling application with new version with updated log. Why not attach .pdb's, and get full info then. Remote Access was only a partial solution to this which should help faster find where is the problem.

[gosr]

@Tigran I tried to use the UnhandledException event from your link, didn't give me more info on the exception unfortunately.

[gosr]

@cichy Using .pdb file gave me the info I needed, I got the exact line where the error occurred. Please make an answer and I'll approve...

[Tigran]

@eightx2: considering that this exception doesn't happen always (according to a post) but sometimes, you need to investigate whta client does, in order to get to the point when in that event handler he gets exception. For this you need to log all possible conditions. By the way, if you have a possibility to access the client's machine, and/or make him to remake the problem, PDB suggested by CICHY is better choice. In my answer I assumed that you have no access and flexibility from the client.