使用ajax获取值

I have a list defined in my controller. Now i want to get user input ,check if it exists in list in controller and then get all it related value.

Controller

private List<M> Ma()
   {
     List<M> md = new List<M>()
      { 
      new M{ R="a", A=300, T= 1, P=40, N=1200},
      new M{ R="Bl", A=100, T= 150, P=400, N=1200},
       };
      return mapData;
   }

Your controller should look like this:

public ActionResult DashData(double a)
{
    return Json(md.FirstOrDefault(map=>map.a == a));
}

While md is the List you defined first

then ur AJAX call should be like this:

    $.ajax({
            url: "../Home/DashData",
            type: "POST",
            data: {'a':a},
            success: function (data) {
                qv.val(data.a);
            }
        });

Firstly, change the ajax call to

var a = $('input').val();
var qv = $('.act');
var tv = $('.tot'); // you don't seem to use this
$.ajax({
  url: '@Url.Action("DashData", "Home")', // never hard code the url!
  type: "POST",
  data: { a: a }, // change this
  success: function (data) {
    // access the properties of the object
    var A = data.A; // returns 300
    var T = data.T; // returns 1
    var P = data.P; // returns 40
    var N = data.N; // returns 200
  }
});

Side notes:

1. var a = $('input').val(); will always return the value of the first <input> in the view, so suggest you use the id attribute ($('#myInput').val();)
2. You can also simplify it to $.post('Url.Action("DashData", "Home"), {a: a }, function(data) { ... })

Next modify the controller method to accept the parameter your passing and return the matching Map object

public ActionResult DashData(string a)
{
  // Get the first matching MapModel
    MapModel map = MapData().FirstOrDefault(m => m.R == a);
    return Json(map);
}