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Use TempData Keep or Peek method to persist data in MVC

TempData used to transfer data between controllers or between actions. There is one point to note that TempData is only work during the current and subsequent request and it is generally used to store one time message.
But one can persist data in TempData object even after request completion with the help of Keep() or Peek() method.

TempData.Keep(): TempData.Keep() method keep value in TemData object at the end of current request. There are two overloaded keep methods available with TempData:
·         void Keep(): This method make ensures that all the items in TempData are not destroyed on current request completion.
·         void Keep(string key): One can persist the specific item in TempData by passing in the item name.

TempData.Peek(string key): It returns an object that contains the element that is associated with the specified key, without marking the key for deletion.

//Set some value to TempData
TempData["value"] = "some value";

//Get value from TempData and marking TempData for deletion.
var val = TempData["value"];

//Decide to retain the value.
//Keep all items.

//Keep specific item named as value.

//Read and retain value at the end of the request in a single request using Peek.
val = TempData.Peek("value");

Difference between Keep() and Peek() method: Both method used to retain the value at the end of request and if you are wondering what is the difference then here it is:
Keep Method
Peek Mthod
To read and retain the value with Keep one need to do two request, i.e. first read the value and in next statement call Keep method to retain value.
With the help of Peek method one can do both operation in a single statement i.e. access as well retain value.
Keep method can be overloaded, i.e. one can keep all items or pass the key to retain specific item.
There is no overloaded method in case of Peek method.
RedirectResult and RedirectToRouteResult internally calls Keep method to retain items
Peek method is not called internally with any of ActionResult.

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