How to prevent special characters in datagridview using vb.net

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VB

validation

DataGridView

I have a windows forms vb.net program that uses a datagridview. I'm trying to find a way to prevent a user from entering special characters (e.g. $,@,!,#,%,^,&) in my datagridview. When the user inputs a special character I have an approprioate message box appear explaining their mistake, then I provide them a default value. I have everything working except a way to prevent the special character or symbols. I'm thinking something like this has to work, but I can't seem to find any way of preventing this sort of entry:

If (columnindex = 0) Then 'checking value for column 1 only
            Dim cellString = DataGridView1.Rows(rowindex).Cells(columnindex).value
            If cellString String.IsSymbol(cellString) = true Then

                    MessageBox.Show("Special Characters Not Allowed")
                End If
                DataGridView1.Rows(rowindex).Cells(columnindex).value = "Default Value"
                Exit Sub
            End If