jQuery的：

jQuery.ajax({
    url: 'AddToCart.aspx/AddTo_Cart',type: "POST",data: "{'quantity' : " + total_qty + ",'itemId':" + itemId + "}",contentType: "application/json; charset=utf-8",dataType: "json",beforeSend: function () {
                  alert("Start!!! ");
               },success: function (data) {
                 alert("a");
              },failure: function (msg) { alert("Sorry!!! "); }
    });

C#代码：

[System.Web.Services.WebMethod]
public static string AddTo_Cart(int quantity,int itemId)
{
    SpiritsShared.ShoppingCart.AddItem(itemId,quantity);      
    return "Add";
}

但它总是调用page_load.我该如何解决？