Knockout.js随手记(4)

动态绑定下拉列表

　　　在<select> data-bind的options选项如果绑定到ko.observableArray()，就可以动态新增选项效果，也就是可以利用其完成常见的级联效果的。

在这一篇文章中，我们用单页面完成无刷新的前台新增选项和使用MVC完成后台的动态添加2个例子。

范例一：

ViewModel中声明一个selectOptions属性为一个ko.observableArray()对象，并将其设为<select>的options下拉列表的数据源，再用两个<input>分別输入入Text及Value，输入內容点击新增按钮，此時就可看到下拉列表出現新增的选项內容。

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
  <title>动态新增下拉列表选项</title>
    <script src="Scripts/jquery-2.0.3.js"></script>
    <script src="Scripts/knockout-2.3.0.js"></script>
   <script type="text/javascript">
       //创建一个View对象
       function ViewModel() {
           var self = this;
           //使用observableArray进行绑定可以动态变更option选项
           self.selectOptions = ko.observableArray([
                { "text": "请选择", "value": "0" }
           ]);
           self.result = ko.observable("0");//添加result监控属性，初始绑定值为0
       }

       $(function () {
           var vm = new ViewModel();
           ko.applyBindings(vm);
           $("#btnAddItem").click(function () {
               vm.selectOptions.push({
                   "text": $("#txtOptText").val(),
                   "value": $("#txtOptValue").val()
               });
           });
       });
   </script>
    </head>
<body>
    <div style=" background-color:#0094ff; width:180px; margin:100px auto auto auto;">
        <select style="background-color:ActiveCaption;width:100px" data-bind="options: selectOptions, optionsText: 'text', optionsValue: 'value', value: result"></select>Value=<span data-bind="    text: result"></span>
        <div> Text: <input id="txtOptText" value="选项1"/></div>
        <div>Value: <input id="txtOptValue" value="1" /></div>
        <input type="button" value="新增选项" id='btnAddItem' />
 </div>
</body>
</html>

运行效果如下：

范例二：Mvc结合knockout.js完成级联下拉菜单

本例只是为了模拟，所以数据比较简陋，当然也可以从数据库中出数据来进行处理。

@{
    Layout = null;
}

<!DOCTYPE html>

<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
    <script src="~/Scripts/jquery-2.0.3.js"></script>
    <script src="~/Scripts/knockout-2.3.0.debug.js"></script>

    </head>
    <body>
      <p>
        <b style="color:#0094ff">选择学生:</b> @Html.DropDownList("Student", ViewBag.Students  as SelectList, "请选择", new { onchange = "searchLover();" })
     </p>
      <p data-bind="visible: selectOptions().length > 0">
      <b style="color:#0094ff">喜爱的事物:</b>
      <select data-bind="options: selectOptions, optionsText: 'Name', optionsValue: 'Value', optionsCaption: '请选择'">
      </select>
</p>
    </body>
    <script type="text/javascript">
        function ViewModel() {
            this.selectOptions = ko.observableArray([]);
        }
        var vm = new ViewModel();
        ko.applyBindings(vm);
        function searchLover() {
            var id= $("#Student").val();
            $.getJSON(
                   "@Url.Action("GetLovers")",
                    { studentId: id},
                    function (data) {
                        vm.selectOptions(data);
            });
        }
</script>
</html>

-------------------------------------Controller中的数据模拟代码------------------------------------

using System.Collections.Generic;
using System.Web.Mvc;

namespace KnockFunctionDemo.Controllers
{
    public class HomeController : Controller
    {
        public ViewResult Index()
        {
            ViewBag.Students = new SelectList(GetStudentList(),"Id","Name");
            return View();
        }
        private static List<Student> GetStudentList()
        {
            return new List<Student>
            {
                new Student{ Id=001, Name="halower"},
                 new Student{ Id=002, Name="rohelm"}
            };
        }
        public JsonResult GetLovers(int studentId)
        {
            var list = new List<Lover>();
            if (studentId == null)
                list= null;
            else if (studentId == 001)
            {
                list.Add(new Lover { Name = "编程", Value = "program" });
                list.Add(new Lover { Name = "女朋友", Value = "GF" });
            }
            else
            {
                list.Add(new Lover { Name = "旅游", Value = "travel" });
                list.Add(new Lover { Name = "家庭", Value = "family" });
            }
            return  Json(list, JsonRequestBehavior.AllowGet);
        }
        
    }

   
    public class Student
    {
        public int Id { get; set; }
        public string Name { get; set; }
    }

    public class Lover
    {
        public string Value { get; set; }
        public string Name { get; set; }
    }
}