Question

I have a combo box on an MVC3 application. When a new item is selected it does a post back as I want it to. All fine there. In the process I pop in a querystring and read it on page load. When the page refreshes it reads the query string and sets the other controls as needed.

However, I need to detect when the page reloads, that it is as a result of a postback, as opposed to the first time the page loads. This is because when the page loads initially, everything is messed up until someone picks something from the combobox.

However, a new user to the site wont know that and will just see a mess.

I understand that MVC3 apps don’t have the same isPostback as ASP.Net has and for various reasons that I don’t understand, I know it is somehow not considered “accaptable”.

However, I am just interested in knowing if there is a 100% guaranteed reliable way to differentiate between a page first loading, and a postback in the same manner as was done in ASP.Net. If there is such a way, what is it and how can I implement it.

I have seen other post’s that do this:

    public bool IsPostBack
    {
        get
        {
            return ViewBag.IsPostBack = (Request.HttpMethod == "POST");
        }
    }

but I read other places that this is always true. So therefore if this is always true it will be true on first load too and in so being, I cant tell reliably if it is a postback or not. I know of course it is a postback of some sort. But it is not if it is a first load.

Can anyone help me with an answer to this please. Also I am using the Razor view engine as opposed to standard aspx view engines.

Answer 1

In MVC, you typically have different actions for GET and POST:

[HttpGet] // Actions are GET by default, so you can omit this
public ActionResult YourAction(int id)
{
    // GET
}

[HttpPost]
public ActionResult YourAction(YourModel model)
{
    // POST
}

If you follow this pattern, there is no need to worry about a Page.IsPostBack-like property.