Question

I want to save GridView cells in a list to compare it with another list.

This is what I tried:

        BudgetCommessa budgetCommessa = new BudgetCommessa();
        List<BudgetCommessa> listaDaGridView = new List<BudgetCommessa>();
        for (int i = 1; i <= preventivoView.Rows.Count; i++)
        {
            budgetCommessa.Task = Convert.ToString(preventivoView.SelectedRow.Cells[0].Text);//SelectedDataKey.Values[0]);
            listaDaGridView.Add(budgetCommessa);
        }

but i get a NullReferenceException even if the cell (0,0) of the GridView is populated

Answer 1

You should check if your gridview has any selected row. Apart from that, there are other problems in your code:

1. Loop should start with 0 and should continue with Rows.Count - 1.
2. You should instantiate budgetCommesa inside the for loop, otherwise you will end up with a list of object all pointing to the same value.

So your code should be like:

for (int i = 0; i < preventivoView.Rows.Count; i++)
 {
        if(preventivoView.SelectedRow != null)
            {            
            BudgetCommessa budgetCommessa = new BudgetCommessa();
            budgetCommessa.Task = Convert.ToString(preventivoView.SelectedRow.Cells[0].Text);//SelectedDataKey.Values[0]);
            listaDaGridView.Add(budgetCommessa);
            }
 }

If you are looking to get value from a cell from all rows, irrespective of selected then, you have to iterate each Row, instead of SelectedRow:

for (int i = 0; i < preventivoView.Rows.Count; i++)
 {
    BudgetCommessa budgetCommessa = new BudgetCommessa();
    budgetCommessa.Task = Convert.ToString(preventivoView.Rows[i].Cells[0].Text);//SelectedDataKey.Values[0]);
    listaDaGridView.Add(budgetCommessa);
 }