NullReferenceException in string.IsNullOrWhiteSpace() and string.IsNullOrEmpty()

Question

I'm checking the cell values of cells of a column that might or not be empty/null so I needed something to avoid a NullReferenceException.

How do I do that since even with the IsNullOrWhiteSpace() and IsNullOrEmpty() I get that exception somehow.

Here's part of the code I'm using:

s = "Total = " + dataGridView1.Rows[0].Cells.Count +
    "0 = " + dataGridView1.Rows[0].Cells[0].Value.ToString() +
    "/n  1 = " + dataGridView1.Rows[0].Cells[1].Value.ToString() +
    "/n  2= " + dataGridView1.Rows[0].Cells[2].Value.ToString() +
    "/n  3 = " + dataGridView1.Rows[0].Cells[3].Value.ToString() +
    "/n  4= " + dataGridView1.Rows[0].Cells[4].Value.ToString() +
    "/n  5 = " + dataGridView1.Rows[0].Cells[5].Value.ToString() +
    "/n  6= " + dataGridView1.Rows[0].Cells[6].Value.ToString() +
    "/n  7 = " + dataGridView1.Rows[0].Cells[7].Value.ToString();

    if (string.IsNullOrEmpty(dataGridView1.Rows[0].Cells[8].Value.ToString()))
    {

    }
    else
    {
        s += "/n  8 = " + dataGridView1.Rows[0].Cells[8].Value.ToString();
    }

I've tried those methods I've tried putting it ==null, I've tried !=null. What else is there or what am I doing wrong exactly and how do I do it right?

I usually use as in this situation: string.IsNullOrEmpty(dataGridView1.Rows[0].Cells[8].Value as string). as will return null if Value is not a string or is null. Also assuming of course that this particular exception is because Value is null. Do note, however, that my example is semantically different from attempting to call ToString on something, as that will work for any type. — Adam Houldsworth
– Adam Houldsworth, Commented Oct 31, 2013 at 14:51
Almost all cases of NullReferenceException are the same. Please see "What is a NullReferenceException in .NET?" for some hints. — John Saunders
– John Saunders, Commented Oct 31, 2013 at 14:52
.ToString() never returns null (in the .NET Framework - you could of course write one that does), so your test with .IsNullOrEmpty is pointless against null. In fact, you probably get the exception from calling .ToString() on a value that is null. — Kris Vandermotten
– Kris Vandermotten, Commented Oct 31, 2013 at 14:54

Jens Kloster · Accepted Answer · 2013-10-31 14:54:31Z

5

the are a lot of places you code could throw that exception ..

dataGridView1.Rows[0]  //here
             .Cells[0] //here
             .Value    //and here
             .ToString()

I belive you don't need the ToString() just type:

"... "+ dataGridView1.Rows[0].Cells[0].Value

in your ifstatement do this:

if (string.IsNullOrEmpty(dataGridView1.Rows[0].Cells[8].Value as string))

answered Oct 31, 2013 at 14:54

Jens Kloster

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Comments

John Saunders · Accepted Answer · 2013-10-31 15:02:00Z

Many people don't understand how to diagnose a NullReferenceException. Consider the following:

dataGridView1.Rows[0].Cells[3].Value.ToString()

Many parts of this could be null. It's the same thing as

var a = dataGridView1.Rows;
var b = a[0];
var c = b.Cells;
var d = c[3];
var e = d.Value;
var f = e.ToString();

If a is null, then a[0] will throw a NullReferenceException. If b is null, then b.Cells will throw a NullReferenceException, etc.

You simply have to figure out which of these is null in your particular situation. The simplest way is to use the debugger. Set a breakpoint before the line that throws the exception. Then hover the mouse over various parts of the expression to see which are null, or use the "Watch" window to enter parts of the expression.

When you find a null, you can stop looking for your NullReferenceException.

Alex Walker · Accepted Answer · 2013-10-31 14:51:52Z

0

You can add an extra line of code to check and handle the null case.

var value = dataGridView1.Rows[0].Cells[0].Value;
string s = (value == null ? string.Empty : value.ToString());

If value is null, then ToString() will not be evaluated and the program cannot throw NullReferenceException.

answered Oct 31, 2013 at 14:51

Alex Walker

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Comments

Tomtom · Accepted Answer · 2013-10-31 14:53:05Z

0

I think in dataGridView1.Rows[0].Cells[8].Value.ToString() you will get a NullReferenceException if the Value is null. So you should check for dataGridView1.Rows[0].Cells[8].Value != null and then you can convert it to a string

answered Oct 31, 2013 at 14:53

Tomtom

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