How can i prevent the program from crashing due to null data

Question

I'm using Datagridview to get data from my sql server. I'm trying to change color of the cell according to their value. However, if there is a null data on the column, it crashes. I'm using .NET Framework 4.0. Here is the code:

 private void MyDataGrid()
    {
        foreach (DataGridViewRow row in MyDataGrid.Rows)

        {
            var cell = row.Cells[5];
            int val = Convert.ToInt32(cell.Value);
            if (val < 0)
            {
                cell.Style.BackColor = Color.Red;
            }
            else if (val > 0)
            {
                cell.Style.BackColor = Color.Green;
            }

        }
    }

This is the error:

An unhandled exception of type 'System.InvalidCastException' occurred in mscorlib.dll

Additional information: Object cannot be assigned to other types from DBNull.

Do favor [Int32.TryParse](https://learn.microsoft.com/en-us/dotnet/api/system.int32.tryparse?view=net-5.0) — LarsTech, Jul 15 '21 at 14:35
compare DBNull.Value with cell.Value ... if they are equals then yous should not execute your code — Selvin, Jul 15 '21 at 14:37
@LeiYang catching expected exception ... interesting (but obviously wrong) approach — Selvin, Jul 15 '21 at 14:39
@Selvin You're right. I forgot the Cell.Value is an object. I usually have a DataSource to avoid those issues. — LarsTech, Jul 15 '21 at 14:40
the OP wants to solve crash. and doesn't specify what to do with null value. so i think try catch and just ignore is ok. — Lei Yang, Jul 15 '21 at 14:43
@LeiYang if you had toothache you can simply extract a tooth but maybe you should try something less invasive first ... [catching exception is very costly](http://www.developerfusion.com/article/5250/exceptions-and-performance-in-net/) — Selvin, Jul 15 '21 at 14:49

Dionis Takac · Answer 1 · 2021-07-15T15:22:27.680

0

It happens in the row where you use Convert.ToInt32(). You can add condition to check if cell.Value is null. I am not sure what you want to do with those kind of values but you can skip showing it by using 'continue' which will skip current iteration and goes to next:

private void MyDataGrid()
        {
            foreach (DataGridViewRow row in MyDataGrid.Rows)
            {
                var cell = row.Cells[5];

                if (cell.Value == null || cell.Value == DBNull.Value) 
                    continue;

                int val = Convert.ToInt32(cell.Value);
                if (val < 0)
                {
                    cell.Style.BackColor = Color.Red;
                }
                else if (val > 0)
                {
                    cell.Style.BackColor = Color.Green;
                }

            }
        }

edited Jul 15 '21 at 15:22

answered Jul 15 '21 at 14:39

Dionis Takac

91
5

I already tried this one, doesn't works. – Swen22 Jul 15 '21 at 14:41
1

compare it to `DBNull.Value` – Selvin Jul 15 '21 at 14:42
2

`if (cell.Value == null || cell.Value == DBNull.Value) continue;` – Jimi Jul 15 '21 at 14:50
it works, thank you so much! @Selvin,@Jimi. – Swen22 Jul 15 '21 at 14:56
i think code style `cell.Style.BackColor = val < 0 ? Red : Green` just fits here. – Lei Yang Jul 15 '21 at 15:12

How can i prevent the program from crashing due to null data

1 Answers1