C# - Inserting An Item Using FormView Control?

I am attempting to insert an items using a basic FormView control.

The FormView has standard entries like:

ItemName
ItemPrice
ItemSize

It also has controls that will be hidden from the user such as:

ItemDateCreated
ItemDatechanged
ItemChangedBy

..These items I am attempting to modify their values before the Insert() takes place, so I have captured the event InsertButton_Click():

protected void InsertButton_Click(object sender, EventArgs e)
{
LinkButton btnInsert = (LinkButton)FormView1.FindControl("InsertButton");
TextBox txtDateAdded = (TextBox)FormView1.FindControl("ItemDateAddedTextBox");

[Code]....

It keeps telling me that the ItemName field is NULL, and throws an error, even though I can plainly see the value is being set in the textbox. Why is this value being thrown as NULL? Do I need to manually create the INSERT statement before I call the Insert()? How would I go about doing that?