Keeping selected item from dropdown box after page refresh in asp web form

问题

I have a aspx page that has several drop down list. So when the users forget to input some values i have to show an error to user, but every DDL are initialized again, and the users information are lost, how can I avoid this ?

When the users forget to input values i return them to current url

url1=www.spadsystem.com
Response.Redirect(Url1);

I heard that we can avoid this problem by using something like absolute i am not sure.

回答1:

Use SessionState object to store the SelectedIndex property of ComboBox (e.g. Cmb), then apply it in Page_Load() event.

Example 1: Store value in Session

int _idx = Cmb.SelectedIndex;
Session["idx"] = _idx.ToString();

Example 2: Read from Session and apply to ComboBox:

Cmb.SelectedIndex = (int)(Session["idx"]);

More details at: http://msdn.microsoft.com/en-us/library/vstudio/ms178581%28v=vs.100%29.aspx

Rgds,

回答2:

Avoid redirecting to another page and back to show the error, and ensure you initialize the lists if IsPostBack is false. Then, the ASP.NET Viewstate will take care of it all for you and keep all the selected values.

回答3:

First of all do not redirect the user when its not required.

Secondly use RequiredFieldValidator for your Fields. It will prevent the postback when your users forget to input any value.

And thirdly, if you are Binding dropdownlists programetically, do that in

If(!IsPostBack)
{
   //Your ddl initialization here
}

This will ensure you get the selected values from DropDownLists

回答4:

agree with use RequiredFieldValidator. and, controls should hold their values if view state is on for the control (check properties).

来源：https://stackoverflow.com/questions/24468464/keeping-selected-item-from-dropdown-box-after-page-refresh-in-asp-web-form