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I am learning ASP.net MVC5 with the code in book.

public ActionResult DemoTempData()
{
    ViewData["Msg1"] = "From ViewData Message.";
    ViewBag.Msg2 = "From ViewBag Message.";
    TempData["Msg3"] = "From TempData Message.";
    return RedirectToAction("Redirect1");
}

public ActionResult Redirect1()
{
    TempData["Msg4"] = TempData["Msg3"];
    return RedirectToAction("GetRedirectData");
}

public ActionResult GetRedirectData()
{
    return View();
}

GetRedirectData view:

@{
    ViewBag.Title = "GetRedirectData";
}

<h2>GetRedirectData</h2>
<ul>
    <li>ViewData-Msg1：@ViewData["Msg1"]</li>
    <li>ViewBag-Msg2：@ViewBag.Msg2</li>
    <li>TempData-Msg3：@TempData["Msg3"]</li>
    <li>TempData-Msg4：@TempData["Msg4"]</li>
</ul>

I know that ViewData and ViewBag will not pass value. The Msg3 and Msg4 in view should have value, but it doesn't. I check the value in Redirect1(), it turns out that Msg3 is null.
I am very confused with what's going on.

Koopakiller
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Echo
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    `@TempData["Msg3"]` in the view will not have a value (`TempData` only lasts one request). But `@TempData["Msg4"]` should have a value - are you saying that is also `null`? –  Aug 21 '17 at 10:01

2 Answers2

4

ASP.NET MVC TempData stores it’s content in Session state. So TempData gets destroyed immediately after it’s used in subsequent HTTP request.

In your case you are assigning the TempData["Msg3"] to TempData["Msg4"]. So once you consume the content from TempData["Msg3"] it gets destroyed. So whenever you try to access TempData["Msg3"] you get null value.

The Peek and Keep methods allow you to read the value without getting destroyed.

reference :

https://msdn.microsoft.com/enus/library/system.web.mvc.tempdatadictionary.peek(v=vs.118).aspx 

object value = TempData["value"];

TempData.Keep("value");

object value = TempData["value"];
Mannan Bahelim
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-3

in the controller Use the builtin Session plumbing, it stays with you until you destroy it. I like it because it always works, and its easy. It is available in

System.Web.HttpContext

which is really the current request

to save use (Example)

System.Web.HttpContext.Current.Session["Msg3"] =  StringOfIds;

To retrieve...

string msg3= (string) System.Web.HttpContext.Current.Session["Msg3"];
alikuli
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