How to solve this error?

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Object reference not set to an instance of an object.<br />
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. <br />
<br />
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 265:        System.IO.StringWriter sw = new System.IO.StringWriter();
Line 266:        HtmlTextWriter htw = new HtmlTextWriter(sw);
Line 267:        gvWarden.HeaderRow.Style.Add("background-color", "#FFFFFF");
Line 268:
Line 269:        //Applying stlye to gridview header cells

What I have tried:

C#

Response.ClearContent();
        Response.AddHeader("content-disposition", "attachment; filename=WardenCoverage.xls");
        Response.ContentType = "application/excel";
        System.IO.StringWriter sw = new System.IO.StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        gvWarden.HeaderRow.Style.Add("background-color", "#FFFFFF");

        //Applying stlye to gridview header cells

        for (int i = 0; i < gvWarden.HeaderRow.Cells.Count; i++)
        {
            gvWarden.HeaderRow.Cells[i].Style.Add("background-color", "#507CD1");
        }

        gvWarden.RenderControl(htw);

Posted 12-Jul-18 4:44am

Member 13878450

Updated 12-Jul-18 5:03am

Tejas Vaishnav

v2

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F-ES Sitecore · Answer 1 · 2018-07-12T04:54:00

This question is asked every day, please do basic research such as using google before you ask a question.

gvWarden.HeaderRow.Style.Add("background-color", "#FFFFFF");

Either gWarden is null, HeaderRow is null, or Style is null. We can't run your code so can't tell you which, and can't tell you why. Use the debugger to find out what is null, then try and work out why it is null.

OriginalGriff · Answer 2 · 2018-07-12T05:04:00

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!

How to solve this error?

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