Question

If I redirect to a new page passing TempData to initialise the page it works fine, however if the user presses the refresh button in their browser the TempData is no-longer available.
Given this, is there any situation where TempData could be used reliably?
Or any way to remove or mitigate the problem of users refreshing?

Answer 1

In MVC 1, yes, temp data is lost after the next request after you store a key.

With MVC 2 however, the temp data is lost after the first attempt to access it.

You can always use Session, which TempData uses anyway, to solve the temp data loss issue your having.

From the MVC 2 Beta Release Notes:

TempDataDictionary Improvements

The behavior of the TempDataDictionary
class has been changed slightly to
address scenarios where temp data was
either removed prematurely or
persisted longer than necessary. For
example, in cases where temp data was
read in the same request in which it
was set, the temp data was persisting
for the next request even though the
intent was to remove it. In other
cases, temp data was not persisted
across multiple consecutive redirects.

To address these scenarios, the
TempDataDictionary class was changed
so that all the keys survive
indefinitely until the key is read
from the TempDataDictionary object.
The Keep method was added to
TempDataDictionary to let you indicate
that the value should not be removed
after reading. The
RedirectToActionResult is an example
where the Keep method is called in
order to retain all the keys for the
next request.

You can also look directly in the MVC 2 source to see these changes:

MVC 1:

  public object this[string key] {
        get {
            object value;
            if (TryGetValue(key, out value)) {
                return value;
            }
            return null;
        }
        set {
            _data[key] = value;
            _modifiedKeys.Add(key);
        }
    }

MVC 2:

   public object this[string key] {
        get {
            object value;
            if (TryGetValue(key, out value)) {
                _initialKeys.Remove(key);
                return value;
            }
            return null;
        }
        set {
            _data[key] = value;
            _initialKeys.Add(key);
        }
    }