Availability of e.Item.DataItem in DataGrid?

[Dave]

I'm trying to understand when DataItem will be available to use as follows:

DataRowView rowData = (DataRowView)(e.Item.DataItem);
int someId = (int)(rowData["someId"]);

I found that e.Item.DataItem is available in DataGrid ItemDataBound such as

private void dgMyDataGrid_ItemDataBound(Object sender, DataGridItemEventArgs
e)

But not in Update method as in

private void dgCompanyCodes_Update(Object sender, DataGridCommandEventArgs e)

I guess I don't know why? Otherwise I have to use the following.

string myId= e.Item.Cells[0].Text;