Beginning ASP.NET 4.5 in CSharp and VB Opsylum

786 x APPENDIX A EXERCISE ANSWERS
DropDownList control, which you can accomplish with the following code in the Page_Load
method:
VB.NET
Protected Sub Page_Load(sender As Object, e As EventArgs) Handles Me.Load
If Not Page.IsPostBack Then
Dim genreId As String = Request.QueryString.Get("GenreId")
If Not String.IsNullOrEmpty(genreId) Then
DropDownList1.DataBind()
Dim myItem As ListItem = DropDownList1.Items.FindByValue(genreId)
If myItem IsNot Nothing Then
myItem.Selected = True
End If
End If
End If
End Sub
C#
protected void Page_Load(object sender, EventArgs e)
{
if (!Page.IsPostBack)
{
string genreId = Request.QueryString.Get("GenreId");
if (!string.IsNullOrEmpty(genreId))
{
DropDownList1.DataBind();
ListItem myItem = DropDownList1.Items.FindByValue(genreId);
if (myItem != null)
{
myItem.Selected = true;
}
}
}
}
Only when the page loads from a new request (and not from a postback) does this code fire. The
code then tries to find a GenreId in the query string. If it can find it, it tries to find an item with that
requested value in the DropDownList. Because the DropDownList control hasn’t been data bound
yet it doesn’t contain any items. Therefore, you need to call DataBind() first. This gets the genres
from the database using EF and puts them in the DropDownList. Once that’s done and the item is
found in the Items collection, it’s made the active item by setting its Selected property to True/
true. The SqlDataSource control watches this DropDownList so when the data source gets its
reviews, it does so for the correct genre.
Exercise 3 Solution
The various data-bound controls can raise exceptions that you can handle in their event handlers.
Once you have dealt with the exception appropriately, you need to set the ExceptionHandled property
of the e argument to True. The following code snippet shows how a Label control is updated