How get? Updating table error: Parameter name: index

Question

I have two tables:

TotalItems :

ItemID (int)
ItemName (Nvarchar)
ItemNumbers (int)

Items :

ID (int)
ItemName (Nvarchar)
Numbers (int)
ItemID (int)

My Items in TotalItems as:

ItemID ItemName ItemNumbers 
1001    Item1       200 
1002    Item2       220
1003    Item3       230
1004    Item4       220
1005    Item5       200

I select 3 Items from TotalItems and add them in wpf DataGrid as:

ID  ItemName    Numbers     ItemID
1   Item1         2          1001
2   Item2         3          1003
3   Item5         6          1005

I want to save them into Items so that ItemNumbers must be updated as:

Item1: 200 - 2 = 198
Item2: 220 - 3 = 217 
Item5: 200 - 6 = 194 

Finally, in TotalItems we must have:

ItemID  ItemName    ItemNumbers
1001    Item1       198
1002    Item2       217
1003    Item3       230 
1004    Item4       220 
1005    Item5       194 

// snippet for update of TotalItems
for (int i = 0; i < gridItem.Items.Count - 1; i++)
    {
    DataBase db = new DataBase();
    DataTable dt = new DataTable();

    string a = gridItem.SelectedCells[2].ToString();
    int b=0;
    b = Convert.ToInt32(gridItem.SelectedCells[3].IsValid.ToString());

    int count, c;
    c = int.parse(comboBox1.Text);
    count = c-b;
    //Updating TotalItems table:
    db.DoCommand("update TotalItems set ItemNumbers='" + count.ToString() + "'where ItemName='" + a + "'");
    }

My problem is ( Specified argument was out of the range of valid values. Parameter name: index ):

string a = gridItem.SelectedCells[2].ToString();

and

b = Convert.ToInt32(gridItem.SelectedCells[3].IsValid.ToString());

Answer 1

Your main problem is that you're trying to access the selected cells in every row, which will not work unless the user has selected every individual cell; this is why you're getting an invalid index exception.

Instead of looping through rows this way, why not just look at the actual underlying data structure? Since you included a DataTable in your question, try something like:

private void ButtonBase_OnClick(object sender, RoutedEventArgs e)
{
    try
    {
        DataBase db = new DataBase();
        foreach (var row in gridItems.Items.Cast<DataRowView>())
        {
            int count;
            if (!int.TryParse(comboBox1.Text, out count))
            {
                // Log error
            }

            int b = (int) row["PropertyNameNotIndex"];
            int totalCount = count - b;

            int itemId = (int) row["ItemId"];
            db.DoCommand("update TotalItems set ItemNumbers='" + count.ToString() + "'where ItemName='" + row["ItemName"].ToString() + "'");
        }
    }
    catch (Exception ex)
    {
        // Handle DB connection errors, etc
    }
}

Notice that indexing is done on property/column name, which is going to be a lot more readable and maintainable. I'm not exactly sure what your logic is with checking IsValid, other than it shouldn't make it to the row if it doesn't pass validation.

Answer 2

I used this:

 private void btnSave_Click(object sender, RoutedEventArgs e)
        {
            for (int i = 0; i < gridItem.Items.Count - 1; i++)
            {
                DataRowView drv = gridItem.Items[i] as DataRowView;

                string a = drv[3].ToString();                
                dt = db.MySelect("select ItemNumbers from TotalItems where ItemName='" + a + "'");
                comboBox1.ItemsSource = dt.DefaultView;
                comboBox1.DisplayMemberPath = "ItemNumbers";
                comboBox1.SelectedValuePath = "ItemNumbers";

                int b = 0;
                b = Convert.ToInt32(drv[4]);
                int c, count;
                int.TryParse(comboBox1.Text, out c);
                count = c - b;                
                db.DoCommand("update TotalItems set ItemNumbers='" + count.ToString() + "' where ItemName='" + a + "'");
            }
            MessageBox.Show("Inserted");
        }