Add a lookup fild by the bottom Click, not from Adding Item

Question

Hello how to add to the value by bottom click not from the Adding Item. Only from code:

          protected void Button2_Click(object sender, EventArgs e)
            {
                using (SPWeb witryna = SPContext.Current.Web)
                {
                    SPListItemCollection listItems = witryna.Lists["Szczegoly"].Items;

                    SPListItem item = listItems.Add();
                    item["Kontrakt"] = TextBox1.Text;
                    item["Pracownik"] = TextBox2.Text;
                    item["Dzien"] = TextBox3.Text;
                    item["Procenty"] = TextBox4.Text;
                    item.Update();
                }
            }

Here is My code. How can I choise and add a Value to item["Procenty"] = TextBox4.Text; When I debug it show me that Value is no-writable.

Answer 1

You have to create a SPFieldLookupValue object,

SPFieldLookupValue splkup=new SPFieldLookupValue(TextBox4.Text);
item["Procenty"] = splkup;

Answer 2

What's the internal name of this field? Is it custom?

Assuming that item["Procenty"] is the same as item["PercentComplete"] you could set it with something like this (Note that TextBox.Text returns a string)

//Set item to 10% completet
item["PercentComplete"] = .10;