Could any body explain, when to use
I have a requirement, where I need to set a value in a controller one, that controller will redirect to Controller Two and Controller Two will render the View.
I have tried to use ViewBag, the value gets lost by the time I reach Controller Two.
Can I know when to use and advantages or disadvantages?
Thanks
1)TempData
Allows you to store data that will survive for a redirect. Internally it uses the Session as backing store, after the redirect is made the data is automatically evicted. The pattern is the following:
public ActionResult Foo()
{
// store something into the tempdata that will be available during a single redirect
TempData["foo"] = "bar";
// you should always redirect if you store something into TempData to
// a controller action that will consume this data
return RedirectToAction("bar");
}
public ActionResult Bar()
{
var foo = TempData["foo"];
...
}
2)ViewBag, ViewData
Allows you to store data in a controller action that will be used in the corresponding view. This assumes that the action returns a view and doesn't redirect. Lives only during the current request.
The pattern is the following:
public ActionResult Foo()
{
ViewBag.Foo = "bar";
return View();
}
and in the view:
@ViewBag.Foo
or with ViewData:
public ActionResult Foo()
{
ViewData["Foo"] = "bar";
return View();
}
and in the view:
@ViewData["Foo"]
ViewBag is just a dynamic wrapper around ViewData and exists only in ASP.NET MVC 3.
This being said, none of those two constructs should ever be used. You should use view models and strongly typed views. So the correct pattern is the following:
View model:
public class MyViewModel
{
public string Foo { get; set; }
}
Action:
public Action Foo()
{
var model = new MyViewModel { Foo = "bar" };
return View(model);
}
Strongly typed view:
@model MyViewModel
@Model.Foo
After this brief introduction let's answer your question:
My requirement is I want to set a value in a controller one, that controller will redirect to ControllerTwo and Controller2 will render the View.
public class OneController: Controller
{
public ActionResult Index()
{
TempData["foo"] = "bar";
return RedirectToAction("index", "two");
}
}
public class TwoController: Controller
{
public ActionResult Index()
{
var model = new MyViewModel
{
Foo = TempData["foo"] as string
};
return View(model);
}
}
and the corresponding view (~/Views/Two/Index.cshtml):
@model MyViewModel
@Html.DisplayFor(x => x.Foo)
There are drawbacks of using TempData as well: if the user hits F5 on the target page the data will be lost.
Personally I don't use TempData neither. It's because internally it uses Session and I disable session in my applications. I prefer a more RESTful way to achieve this. Which is: in the first controller action that performs the redirect store the object in your data store and user the generated unique id when redirecting. Then on the target action use this id to fetch back the initially stored object:
public class OneController: Controller
{
public ActionResult Index()
{
var id = Repository.SaveData("foo");
return RedirectToAction("index", "two", new { id = id });
}
}
public class TwoController: Controller
{
public ActionResult Index(string id)
{
var model = new MyViewModel
{
Foo = Repository.GetData(id)
};
return View(model);
}
}
The view stays the same.
ViewBag.Title property on all my Views which gets used in my _Layout.cshtml base view file. Another case where I use it is giving info-messages (e.g. "Product saved successfully!") to the users. I placed some generic markup in Layout.cshtml to render a message if provided and this allows me to set ViewBag.Message in any Action. Using a ViewModel property for either case has too many disadvantages. –
Fairchild ViewBag. Please describe a specific, real world scenario, when ViewBag has some use. Since you are saying that it is, I quote a powerful resource, I guess you have some specific cases where this powerful resource is powerful. Since I've never used it in my career, I would be very happy to learn how people are using this powerful weapon. –
Back Basically it's like a DataReader, once read, data will be lost.
public class HomeController : Controller
{
public ActionResult Index()
{
ViewBag.Message = "Welcome to ASP.NET MVC!";
TempData["T"] = "T";
return RedirectToAction("About");
}
public ActionResult About()
{
return RedirectToAction("Test1");
}
public ActionResult Test1()
{
String str = TempData["T"]; //Output - T
return View();
}
}
If you pay attention to the above code, RedirectToAction has no impact over the TempData until TempData is read. So, once TempData is read, values will be lost.
Check the output in Action Method Test 1 and Test 2
public class HomeController : Controller
{
public ActionResult Index()
{
ViewBag.Message = "Welcome to ASP.NET MVC!";
TempData["T"] = "T";
return RedirectToAction("About");
}
public ActionResult About()
{
return RedirectToAction("Test1");
}
public ActionResult Test1()
{
string Str = Convert.ToString(TempData["T"]);
TempData.Keep(); // Keep TempData
return RedirectToAction("Test2");
}
public ActionResult Test2()
{
string Str = Convert.ToString(TempData["T"]); //OutPut - T
return View();
}
}
If you pay attention to the above code, data is not lost after RedirectToAction as well as after Reading the Data and the reason is, We are using TempData.Keep(). is that
The Data will persist to the corresponding View
ViewBag, ViewData, TempData and View State in MVC
http://royalarun.blogspot.in/2013/08/viewbag-viewdata-tempdata-and-view.html
ASP.NET MVC offers us three options ViewData, VieBag and TempData for passing data from controller to view and in next request. ViewData and ViewBag are almost similar and TempData performs additional responsibility.
Similarities between ViewBag & ViewData :
Helps to maintain data when you move from controller to view. Used to pass data from controller to corresponding view. Short life means value becomes null when redirection occurs. This is because their goal is to provide a way to communicate between controllers and views. It’s a communication mechanism within the server call.
Difference between ViewBag & ViewData:
ViewData is a dictionary of objects that is derived from ViewDataDictionary class and accessible using strings as keys. ViewBag is a dynamic property that takes advantage of the new dynamic features in C# 4.0. ViewData requires typecasting for complex data type and check for null values to avoid error. ViewBag doesn’t require typecasting for complex data type.
ViewBag & ViewData Example:
public ActionResult Index()
{
ViewBag.Name = "Arun Prakash";
return View();
}
public ActionResult Index()
{
ViewData["Name"] = "Arun Prakash";
return View();
}
In View, we call like below:
@ViewBag.Name
@ViewData["Name"]
TempData:
Helps to maintain data when you move from one controller to other controller or from one action to other action. In other words when you redirect, “Tempdata” helps to maintain data between those redirects. It internally uses session variables. TempData is meant to be a very short-lived instance, and you should only use it during the current and the subsequent requests only
The only scenario where using TempData will reliably work is when you are redirecting. This is because a redirect kills the current request (and sends HTTP status code 302 Object Moved to the client), then creates a new request on the server to serve the redirected view.
It requires typecasting for complex data type and check for null values to avoid error.
public ActionResult Index()
{
var model = new Review()
{
Body = "Start",
Rating=5
};
TempData["ModelName"] = model;
return RedirectToAction("About");
}
public ActionResult About()
{
var model= TempData["ModelName"];
return View(model);
}
void Keep()
Calling this method with in the current action ensures that all the items in TempData are not removed at the end of the current request.
@model MyProject.Models.EmpModel;
@{
Layout = "~/Views/Shared/_Layout.cshtml";
ViewBag.Title = "About";
var tempDataEmployeet = TempData["emp"] as Employee; //need typcasting
TempData.Keep(); // retains all strings values
}
void Keep(string key)
Calling this method with in the current action ensures that specific item in TempData is not removed at the end of the current request.
@model MyProject.Models.EmpModel;
@{
Layout = "~/Views/Shared/_Layout.cshtml";
ViewBag.Title = "About";
var tempDataEmployeet = TempData["emp"] as Employee; //need typcasting
TempData.Keep("emp"); // retains only "emp" string values
}
TempData will be always available until first read, once you read it its not available any more can be useful to pass quick message also to view that will be gone after first read. ViewBag Its more useful when passing quickly piece of data to the view, normally you should pass all data to the view through model , but there is cases when you model coming direct from class that is map into database like entity framework in that case you don't what to change you model to pass a new piece of data, you can stick that into the viewbag ViewData is just indexed version of ViewBag and was used before MVC3
Also the scope is different between viewbag and temptdata. viewbag is based on first view (not shared between action methods) but temptdata can be shared between an action method and just one another.
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