Convert contents of DataGridView to List in C#

        List<MyItem> items = new List<MyItem>();
        foreach (DataGridViewRow dr in dataGridView1.Rows)
        {
            MyItem item = new MyItem();
            foreach (DataGridViewCell dc in dr.Cells)
            { 
                ...build out MyItem....based on DataGridViewCell.OwningColumn and DataGridViewCell.Value  
            }

            items.Add(item);
        }

If you bind your list using DataSource, you can convert back by with:

List<Class> myClass = DataGridView.DataSource as List<Class>;

Or a linq way

var list = (from row in dataGridView1.Rows.Cast<DataGridViewRow>()
           from cell in row.Cells.Cast<DataGridViewCell>()
           select new 
           {
             //project into your new class from the row and cell vars.
           }).ToList();