Asp.Net Repeater loses data on postback - asp.net

Question

My problem is a bit more complicated than the title says:
I made a user control (I called it editor) for editing Data base data into another user control I also made(I called it GridView).
The editor is use for each row (a row is also a usercontrol and the editor is only inside row even for insert) inside my gridview and work perfectly but not when I try to use it to insert.
The only difference between insert and edit is this Field:
#region Field
/// <summary>
///
/// </summary>
//public Field Field { get { return DataItem as Field; } }
private Field _field;
[Bindable(true)]
public Field Field
{
get
{
if (IsInsert && _field == null)
{
_field = SubscriptionController.CreateField();
}
return _field;
}
set { _field = value; }
}
#endregion
Inside this Field I've the collection I bind to the repeater
the SubscriptionController.CreateField(); method just create an instance of Field class and all collection inside here is the code:
public Field CreateField()
{
Field field = new Field();
field.Type = GetFieldTypes().First();
field.Label = new LocalizedStringCollection();
field.Values = new FieldValueCollection();
field.Selections = new FieldSelectionCollection();
foreach (Models.TrainingGroup trainingGroup in GetTrainingGroup())
{
foreach (Models.Division division in GetDivisions())
{
foreach (Models.ProfilStatusGroup profilStatusGroup in GetProfilStatusGroup())
{
field.Selections.Add(new Models.FieldSelection() { Selected = false, DivisionId = division.Id, ProfilStatusGroupId = profilStatusGroup.Id, TrainingGroupId = trainingGroup.Id });
}
}
}
}
the collection I bind is stored in viewstate :
#region FieldValues
/// <summary>
/// Get/Set FieldValues from Viewstate
/// </summary>
public FieldValueCollection FieldValues
{
get
{
if (ViewState["FieldValues"] == null)
{
if (Field != null && Field.Values != null)
ViewState.Add("FieldValues", Field.Values);
else
ViewState.Add("FieldValues", new FieldValueCollection());
}
if (ViewState["FieldValues"] != null)
{
return (FieldValueCollection)ViewState["FieldValues"];
}
return null;
}
set
{
if (ViewState["FieldValues"] == null)
{
ViewState.Add("FieldValues", value);
}
else
{
ViewState["FieldValues"] = value;
}
}
}
#endregion
but when I get on postback all textboxes inside my repeater are empty.