make sure you have autopostback set to True
thanks :-)
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DropDownList items lost after postback, when inside a dynamic Panel-type custom control
I have attached a very simple sample of some ASP.NET files that are causing me problems. Inside the ZIP is a cut-down version of a dynamic custom control and an implementing ASP.NET page.
If I put a dropdown list inside the custom control, when it first loads, items are added to the dropdown. After postback, these items are lost. ViewState appears not to be loaded for the dropdown inside the panel.
The panel is added to the custom control's Controls collection, in the CreateChildControls override. I have also tried adding the panel in OnInit, OnLoad, LoadViewState and TrackViewState. All do the same thing and lose the items.
I want to know why ViewState is not loaded for the dropdown inside the panel. I've struggled for over three hours with this now...
J.
PS: I've had to rename all the files in the ZIP to .txt to get around the overly-sensitive extention check on the attachments facility -- remove the .txt extention and import the files into a VS2005 Web App Project.
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Answers
Romasa; the lists are only supposed to populate their items on first load, then cache them into ViewState for subsequent page loads. This works normally (see lst1) but not for the one in the panel (see lst2).
meispisces; AutoPostback is set to true. Not that this should make any difference. Items are supposed to be retained in ViewState, regardless of whether a list calls __doPostback as part of its onchange event.
I think I have worked this out. It just seems that I can't overload Controls to return a ControlCollection from one of my child controls. It would render correctly but postbacks are all messed up.
I rewrote the control to render the elements manually, overriding the RenderStartTag and RenderEndTag methods and it has worked ever since.
Obviously this is the 'correct' way to write a control but I was hoping to perform a couple of shortcuts and it looks like I can't.
J.
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by: RomasaPosted on 2009-09-08 at 22:21:42ID: 25288446
That is creating problem because aspx.cs page call it refreshes all object so
on page load
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
lst1.Items.Add("test1");
lst1.Items.Add("test2");
lst1.Items.Add("test3");
lst2.Items.Add("test1");
lst2.Items.Add("test2");
lst2.Items.Add("test3");
}
}
}
U can add it in aspx page or
call it on other event like on binding