Passing TempData with RedirectToAction

Question

Intro: I am a .NET studet trying to learn ASP.NET Core MVC. So please be understanding. I have searched the web for an answer to my problem, but havent found a solution that works for me.

Problem: I want to pass a validation message from my create post method to the index IActionmethod whenever a post has been created and them show it as an alert message for now. I have read on the web that ViewBag dosent survive a redirect, but a TempData does. This is my code so far.

Create post method:

 public IActionResult CreatePost(string textContent, string headline, string type)
    {

        var catType = new Category() { CategoryType = type.ToUpper() };

        if (db.Category.Any(s => s.CategoryType.Trim().ToLower() == type.Trim().ToLower()))
            catType = db.Category.FirstOrDefault(s => s.CategoryType.Trim().ToLower() == type.Trim().ToLower());


        var newPost = new Post()
        {
            Content = textContent,
            Header = headline,
            DateOfPost = DateTime.Now,
            category = catType

        };
        db.Posts.Add(newPost);
        db.SaveChanges();

        TempData["validation"] = "Your post hase been publsihed";

        return RedirectToAction("Index");
    }

The index method:

public IActionResult Index()
        {

        var validation = TempData["validation"];

            var posts = (from x in db.Posts
                         orderby x.DateOfPost descending
                         orderby x.PostID descending
                         select x);

            return View(posts);
        }

I have tried this guide: ClickThis and this one: ClickThis2 but I got this message:

I know this line from gudie number 2 might be important, but didnt now how to apply it. -

var product = TempData["myTempData"] as Product;

The last thing I want to do is pass it to the index view, but dont know how. I am currently passing a model from the index.

Tell me if it is anything more you would like to see. Like dependencies.

All the help I get is gold and will be much appreciate!!!

Answer 1

I landed on this question while googling for "asp.net core redirect to action tempdata". I found the answer and am posting it here for posterity.

Problem

My issue was that, after filling in some TempData values and calling RedirectToAction(), TempData would be empty on the page that I was redirecting to.

Solution

Per HamedH's answer here: If you are running ASP.NET Core 2.1, open your Startup.cs file and make sure that in your Configure() method app.UseCookiePolicy(); comes after app.UseMVC();.

Example:

public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
    ...

    app.UseMvc(routes =>
    {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
        });
    }

    app.UseCookiePolicy();
}

Answer 2

Did you configure Session? TempData is using session behind the scenes.

Project.json

"Microsoft.AspNetCore.Session": "1.1.0"

Here is the Startup.cs file. - ConfigureServices method

public void ConfigureServices(IServiceCollection services)
{
     services.AddMemoryCache();
     services.AddSession();
     services.AddMvc();
}

And Configure method.

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    app.UseSession();
    app.UseMvc(routes => {
        routes.MapRoute(
            name: "default",
            template: "{controller=Home}/{action=Index}/{id?}");
    });
}

Now try with TempData, it will work.

And you can set the environment with set ASPNETCORE_ENVIRONMENT=Development environment variable.