When value is equal to nothing getting an error even with data checking?

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I have the following part of code:

VB

If IsNothing(strCellValue = tabledgv.Rows(newNum).Cells(1).Value.ToString()) Then

            datetxt.Text = "N/A"
        Else
            datetxt.Text = strCellValue

        End If

As you can see I have isNothing so it should check for that correct? Anyways when I run it I still get an error:

System.NullReferenceException: 'Object reference not set to an instance of an object.'

System.Windows.Forms.DataGridViewCell.Value.get returned Nothing.

What I have tried:

I've tried removing the IsNothing. I also tried using isDBNull as it is a null value on SQL but have fixed that with the .tostring at the end.

Posted 26-Nov-19 6:04am

Cody O'Meara

Updated 26-Nov-19 22:00pm

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[no name] 26-Nov-19 12:35pm

tabledgv.Rows(newNum).Cells(1): Looks like the Row/Col does not exists.

Cody O'Meara 26-Nov-19 13:58pm

Thank you for the response. Correct. Inside the cell there is no value so I'm trying to get it to say "N/A" when there is nothing in the cell.

[no name] 26-Nov-19 14:04pm

I think you misunderstand this. I think the problem is more that tabledgv.Rows(newNum) or then the cell does not exists. This you _can't_ check by accessing tabledgv.Rows(newNum).Cells(1).Value. You need to make sure before that the requested row and also the requested col does exists.

Cody O'Meara 26-Nov-19 14:18pm

I probably am missing something. I have this "totalRows = tabledgv.Rows.GetRowCount(DataGridViewElementStates.Visible) - 1" for getting total rows. It does work as I have a label that displays on load to which is correct amount. I also have this checker"If newNum > totalRows Then newNum = 1 End If" to reset back to the first row which there are 2 rows with data. Happens when trying the second row. This happens before the check to see if strCellValue equals nothing.

[no name] 26-Nov-19 14:52pm

why -1 in totalRows = tabledgv.Rows.GetRowCount(DataGridViewElementStates.Visible) - 1?

2 solutions

Solution 2

You are doing it wrong!

First of all, you can't initiate variable inside IsNothing function, because the underlined part of line is interpreted by compiler like a boolean value (a result of comparison):

VB

If IsNothing(strCellValue = tabledgv.Rows(newNum).Cells(1).Value.ToString()) Then

Boolean value will never return null/nothing!

comparison of strCellValue to the tabledgv cell Value
"" = "" ' returns true
"" = "some value" ' returns false

If your DataGrdView object is bind to the datatable of SQL database, i'd change it to:

VB

If DbNull.Value.Equals(tabledgv.Rows(newNum).Cells(1).Value) Then

For further details, please see:
Comparison Operators - Visual Basic | Microsoft Docs[^]
Information.IsNothing(Object) Method (Microsoft.VisualBasic) | Microsoft Docs[^]
DBNull.Value Field (System) | Microsoft Docs[^]

Posted 26-Nov-19 22:00pm

Maciej Los

Updated 26-Nov-19 22:07pm

v3

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RickZeeland · Accepted Answer · 2019-11-26T06:49:00

Solution 1

In this blog it is advised not to use IsNothing(): Patrick Steele's .NET Blog - Avoiding IsNothing()[^]
Instead you can use:

VB

If tabledgv.Rows(newNum).Cells(1).Value Is Nothing Then
...

Posted 26-Nov-19 6:49am

RickZeeland

Updated 26-Nov-19 6:50am

v2

Comments

Cody O'Meara 26-Nov-19 13:40pm

Thank you for the response RickZeeland. I change it. Now getting Suppression State
Error BC30020 'Is' operator does not accept operands of type 'Boolean'. Operands must be reference or nullable types.

RickZeeland 26-Nov-19 14:44pm

Could it be a Checkbox maybe? then use:
If (tabledgv.Rows(newNum).Cells(1).Value) Then
...