How to get ViewBag or TempData value after ajax request and assign to c# variable in view

Question

I have list on View from the controller, this is initialize when page is load.

@{
    List<SomeClass> list = (List<SomeClass>) TempData["onload"];
}

I assign TempData["onload"] list to kendo treeview and set action("onSelect") when any item selected from treeview. than i have one js function ("onSelect") that fire when i select item from the treeviewlist. code behind the function:

::VIEW::

function(e){
     ...code...
     $.ajax({
        type: "POST",
        url: "/Report/itemSelection_Changed", // the URL of the controller action method
        data: {pid : parentid, cid : currentnodeid}, // optional data
        dataType: "json",

        success: function (result) {
            text = result;
            var yoo = null;
            document.getElementById("descriptionbox").value = text
            if ('@ViewBag.ppi' != null && '@ViewBag.cci' != null) {
                yoo = '@list[ (int) ViewBag.ppi].childrens[ (int) ViewBag.cci].extratxt';
            }
            //here i want to use yoo.
        },
        error: function (req, status, error) {
            text = req.responseText;
            document.getElementById("descriptionbox").value = text;
        }
    });
}

::Controller::

public JavaScriptResult itemSelection_Changed(string pid, string cid)
    {
        ViewBag.ppi = pid;
        ViewBag.cci = cid;
        return JavaScript( "sometext" );
    }

1. after the request the ViewBag.ppi and ViewBag.cci is null. why?
2. and if there is no possibility from ViewBag than there is any other way to set value in controller and get in view as c# variable?