Asp.Net core Tempdata and redirecttoaction not working

Question

I have a method in my basecontroller class that adds data to tempdata to display pop-up messages.

protected void AddPopupMessage(SeverityLevels severityLevel, string title, string message)
{
    var newPopupMessage = new PopupMessage()
    {
        SeverityLevel = severityLevel,
        Title = title,
        Message = message
    };
    _popupMessages.Add(newPopupMessage);
    TempData["PopupMessages"] = _popupMessages;
}

If the action returns a view, this works fine. If the action is calling a redirectotoaction I get the following error.

InvalidOperationException: The 'Microsoft.AspNetCore.Mvc.ViewFeatures.Internal.TempDataSerializer' cannot serialize an object of type

Any thoughts ?

Answer 1

TempData uses Session, which itself uses IDistributedCache. IDistributedCache doesn't have the capability to accept objects or to serialize objects. As a result, you need to do this yourself, i.e.:

TempData["PopupMessages"] = JsonConvert.SerializeObject(_popupMessages);

Then, of course, after redirecting, you'll need to deserialize it back into the object you need:

ViewData["PopupMessages"] = JsonConvert.DeserializeObject<List<PopupMessage>>(TempData["PopupMessages"]);

Answer 2

Another scenario where this type of error happened to me was upgrading from AspNetCore 2.2 to 3.0 - and, where I had AzureAD as an OpenID Connect provider - when it would try to process the AzureAD cookie, it threw an exception the TempDataProvider and complained that it could not serialize a type of Int64. This fixed:

    services.AddMvc()
    .AddNewtonsoftJson(options =>
           options.SerializerSettings.ContractResolver =
              new CamelCasePropertyNamesContractResolver());

https://learn.microsoft.com/en-us/aspnet/core/migration/22-to-30?view=aspnetcore-3.1&tabs=visual-studio#newtonsoftjson-jsonnet-support