Ch 15 exercise 2 don't need to call DataBind

Notso · April 14th, 2012, 11:52 PM

Hi Imar,
In the solution for Ch. 15 exercise 2, you state that "Because the DropDownList control hasn't been data bound yet, it doesn't contain any items. Therefore you need to call DataBind() first."

However, I have found that this code works just fine for me in Reviews.aspx.cs

int _genreId;

protected void Page_Load(object sender, EventArgs e)
{
if (!string.IsNullOrEmpty(Request.QueryString.Get("Ge nreId")) && Page.IsPostBack == false)
{
_genreId = Convert.ToInt32(Request.QueryString.Get("GenreId") );
DropDownList1.SelectedValue = Convert.ToString(_genreId);
}
}

I have run some tests and find that it seems to work for new inserts, editing review without changing genre, and editing review and changing review's genre. Am I missing something here? Is there a case where this isn't going to work? Or are you incorrect about needing to DataBind? Why does this work when I am not calling DropDownList1.DataBind();?

Thanks.

Imar · April 15th, 2012, 04:11 AM

Hi there,

Both solutions are correct, and both would work. By setting the SelectedValue property directly, the control remembers this value, so when it comes to data binding (done by the framework automatically), it knows which item to preselect.

By calling DataBind explicitly, the items are loaded into the control so FindByValue works as well. You can use either solution; however, by calling DataBind you get the actual items in the control at the time of Page_Load, giving you the opportunity to look at the items and add or change them. If you don't need that behavior (as in this exercise where you're only interested in preseleting the correct item) your solution is perfect.

Cheers,
Imar