在datagridview单元格错误中获取价值

Question

I have a datagridview and it contain 5 rows, the column name are: XS,S,M,L, and XL.

And the flow is first The user will choose a brand(CHL and XRA), and if the user choose the XRA, the column names will be rename to -,1L,2L,3L,4L.

What the problem here is that every time I get the value from the cell that the column name is renamed, I'm getting this kind of error: Object reference not set to an instance of an object.

This is my sample code for getting the value from the cell:

dvJOBranch.Rows(0).Cells.Item("M").Value.ToString

This code is perfectly working if do not rename the column, but if I rename the column, its having an error.

Answer 1

If the index of the column does not change, you could access it by its index instead of its name:

dvJOBranch.Rows(0).Cells.Item(2).Value.ToString 'third column

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Note that Object reference not set to an instance of an object means you have a NullReferenceException

The line of code above supposes that:

• dvJOBranch.Rows(0) is not null , otherwise access to Cell will throw a NullReferenceException
• dvJOBranch.Rows(0).Cells.Item(2) is not null , otherwise access to Item(2).Value will throw a NullReferenceException
• dvJOBranch.Rows(0).Cells.Item(2).Value is not null , otherwise call of .ToString() method will throw a NullReferenceException

You need to make appropriate tests to handle null values.

If dvJOBranch.Rows(0).Cells.Item(2).Value IsNot Nothing Then
    (...)
End If

See also What is a NullReferenceException, and how do I fix it?

Answer 2

Try the following:

If dvJOBranch.Rows(0).Cells.Item(2).Value IsNot Nothing OrElse String.IsNullOrEmpty(dvJOBranch.Rows(0).Cells.Item(2).Value.ToString)
(...)
End if

The most important here is the OrElse (in stead of OR), because otherwise the second part of the equasion still gives the NullReferenceException.