How to update a people and group field via code?

Today I was working on my custom web part. One of my questions was : after pressing submit button how to update a people and group field in the destination list.

I tested many ways and they gives me this error :

Invalid data has been used to update the list item. The field you are trying to update may be read only.

after searching and googling for some hours I found it in my way , here it is :

SPListItemCollection itemCollection;
SPListItem item;
PeopleEditor people;
PickerEntity picker;
SPUserInfo userInf;
SPUser user;

itemCollection = web.Lists["ListName"].Items;
item = itemCollection.Add();

// I arranged my controls in a table
// here is my one of people editor controls
// So after pressing submit, the account of this control should set
// new Item "Assigned To" field in the related list.
people = (PeopleEditor)Tbl.Rows[0].Cells[0].Controls[0];  
picker = (PickerEntity)people.ResolvedEntities[0];
userInf = new SPUserInfo();
user = web.EnsureUser(picker.Key);
item["Assigned To"] = user;
item.Update();

with this kind of coding my list start updating correctly ! hope this help you …

Also here is some related links that helped me :

• http://mysharepointblog.com/post/2007/07/How-to-use-the-PeoplePicker-in-SharePoint.aspx
• http://suguk.org/forums/post/13950.aspx
• http://blog.qumsieh.ca/2008/07/21/how-to-use-the-people-editor-control-loading-data-to-a-column-of-type-person-or-group/