ASP.NET MVC Postback - dropdownlist example
In ASP.NET MVC, postback is handled differently then how it is handled in ASP.NET.
If you are starter then you will be searching for ways to do this. In this article I will discuss more about handling dropdownlist in the postback of the ASP.NET MVC view page.
In my previous article I had discussed How to bind IList with MVC dropdownlist. I will use that example in this article. I am using the same master page that comes with standard ASP.NET MVC project in Visual Studio.
Controller Name: PostBackCheck
Action Name: Index
The view page looks like this:
<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage" %>
<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
Index
</asp:Content>
<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
<h2>Index</h2>
<form id="frm_Main1" action="Index" method="post">
<div>
<%=Html.DropDownList("SecretQuestion") %><p/>
<input type="submit" value="Do PostBack" id="submit" name="btnSubmit"/>
</div>
</form>
To populate the dropdownlist with items I have used a method: GetDropdownlistItems()
Method 1: Bind dropdowlist value using FormCollection object:
using
System.Collections.Generic;
using
System.Linq;
using
System.Web;
using
System.Web.Mvc;
using
System.Web.Mvc.Ajax;
namespace
MvcApplication1.Controllers
{
public class PostBackCheckController :
Controller
{
//
// GET:
/PostBackCheck/
public ActionResult
Index()
{
IList<SelectListItem> ilSelectListItems = GetDropdownlistItems
();
ViewData["SecretQuestion"] = ilSelectListItems;
return View();
}
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult
Index(FormCollection frmCollection)
{
string dropDownSelectedValue = frmCollection.Get("SecretQuestion");
IList<SelectListItem> ilSelectListItems = GetDropdownlistItems
();
ViewData["SecretQuestion"] = new SelectList
(ilSelectListItems, "Value", "Text", dropDownSelectedValue);
return View();
}
public IList<SelectListItem> GetDropdownlistItems()
{
//1. Create a new IList of SelectListItems
//2. Add 10 items to the list.
IList<SelectListItem> ilSelectList = new List<SelectListItem>();
for (int cnt = 0; cnt < 10; cnt++)
{
SelectListItem selectListItem = new SelectListItem();
selectListItem.Text = "
selectListItem.Value = cnt.ToString();
ilSelectList.Add(selectListItem);
}
return ilSelectList;
}
}
}
FormCollection object will have all the objects on the form. We can get the dropdownlist selected value using: frmCollection.Get("SecretQuestion").
Method 2: Bind dropdownlist value using the object name. using
System.Collections.Generic;
using
System.Linq;
using
System.Web;
using
System.Web.Mvc;
using
System.Web.Mvc.Ajax;
namespace
MvcApplication1.Controllers
{
public class PostBackCheckController :
Controller
{
//
// GET:
/PostBackCheck/
public ActionResult
Index()
{
IList<SelectListItem> ilSelectListItems = GetDropdownlistItems
();
ViewData["SecretQuestion"] = ilSelectListItems;
return View();
}
[AcceptVerbs(HttpVerbs.Post)]
public ActionResult
Index(string SecretQuestion)
{
IList<SelectListItem> ilSelectListItems = GetDropdownlistItems
();
ViewData["SecretQuestion"] = new SelectList
(ilSelectListItems, "Value", "Text", SecretQuestion);
ViewData["SecretQuestion"] = ilSelectListItems;
return View();
}
public IList<SelectListItem> GetDropdownlistItems()
{
//1. Create a new IList of SelectListItems
//2. Add 10 items to the list.
IList<SelectListItem> ilSelectList = new List<SelectListItem>();
for (int cnt = 0; cnt < 10; cnt++)
{
SelectListItem selectListItem = new SelectListItem();
selectListItem.Text = "
selectListItem.Value = cnt.ToString();
ilSelectList.Add(selectListItem);
}
return ilSelectList;
}
}
}
Here we can get the dropdownlist selected value by accepting it as part of the method signature.
The input parameter name should be the same as the object name.
Hope this helps.