ViewData, ViewBag, TempData and Session in MVC

ViewBag, ViewData, TempData and Session are the options to send value from controller to view or to other action method/pages. ViewData and ViewBag are very straight forward, they used to send the data from controller to view and done but in case of TempData and Session we can pass values from controller to view and even we can get our value from other pages after redirecting. As we know TempData and Session they both are saved into session but their behavior is a little different, in this article we will explore ViewBag and ViewData a little bit and more on TempData and Session with different examples.

Let's take a very simple example of ViewData to pass the data from controller to view and show in view

 // In controller
 ViewData["item"] = "Some string";
 Or
 ViewData("item", "Some string"); 

 // In view
 <div>@ViewData["item"]</div>

It will render the string on the page, very simple, Can we pass object into ViewData, yes we can, let's try it as well,

create a simple class to test it.

 public class Product
 {
    public int Id { get; set; }
    public string Product { get; set; }
 }

 // In controller add to view data
 ViewData["product"] = new Product { Id = 1, Product = "Computer" };

 // In View 
 @{
    var vdProduct = ViewData["product"] as SessionLess.Controllers.Product;      
    <div>
        View Data Values
        <div>
            @vdProduct.Id : @vdProduct.product 
        </div>
    </div>
 }
 //And here is the output:
  View Data Values
  1 : Computer

ViewData Conclusion:

1. ViewData is a dictionary type public ViewDataDictionary ViewData { get; set; }
2. ViewData can be used to pass data from controller to view, one way only
3. ViewData life lies only during the current request
4. If passing string into ViewData then no need to typecast
5. if passing object in ViewData then you need to typecast it but before that you need to check if it is not null
6. ViewData is a property on ControllerBase, which is the parent of Controller class

ViewBag behaves in very similar to ViewData so no need to take examples but just give the Conclusion

1. ViewBag internally use dynamic public dynamic ViewBag { get; }
2. ViewBag can also be used to pass data from controller to view, one way only
3. ViewBag's life also lies only during the current request
4. ViewBag's a dynamic type so not necessary to typecast
5. ViewBag is also a property on ControllerBase, which is the parent of Controller class

TempData

Now time to examine TempData, lets first note it’s feature before applying in code

1. TempData internally use TempDataDictionary public TempDataDictionary TempData { get; set; }
2. Once data is saved into TempDataDictionary object
3. TempData persist in it and can be read from any view or any action in any controller
4. TempData can only be read once, once read, it becomes null
5. TempData Saves into session so on expiration of session data loss
6. This behavior is new from ASP.NET MVC 2 and latter version.
7. In earlier versions of ASP.NET MVC, the values in TempData was available only until the next request
8. TempData’s life, until it is read or session expire and can be read from anywhere

Let's try to examine it:

  // Assign value in action View1
  TempData["item"] = "TempData value to show";

  // To render in view
  TempData : @TempData["item"]

Let's try to render the value from two different views, say view1 and view 3

1. Open View1 : value exits
2. Open View3: Null

Other scenario:

1. Remove the code to read TempData value from view1
2. Open different pages
3. Finally open the page where you written code to read and you will see value exists

It can be handy in some situation like you want to assign once and read only once, say

1. It can be used to pass the value for error message and show on the page and done
2. Store the transaction Id before sending the user to bank site, and once user return match with returned value

As we know now, once temp data is read it will no longer be available, so If we want to keep it after reading it once then we can use Keep pr Peek

@TempData[“MyData”];
TempData.Keep(“MyData”);

First read and then indicate to keep it for further use, but if you want to do the same thing in one line then use Peek like this

var str = TempData.Peek("MyData").ToString();

In this way you can use temp data as many times as you want or you can say in this way it will work like a session.

Session

1. Session stores data into session
2. Session is not similar to TempData to access one but you can read as many time as you want
3. Session never becomes null until or unless session timeout or session expire.
4. Session is not a good practice to use session very frequently or store big data, it hits performance
5. List item

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