Html帮助类
used to render (modify and output) HTML form elements
用来渲染HTML表单元素（修改和输出）
Html.ActionLink
输出: <a href=”..”…>..</a>
Html.BeginForm
输出: <form …>
Html.CheckBox
输出: <input type="checkbox" …/>
Html.DropDownList
输出: <select ..> .. </select>
Html.EndForm
输出: </form>
Html.Hidden
输出: <input type="hidden" ... />
Html.ListBox
输出: <select multiple …>…</select>
Html.Password
输出: <input type="password" … />
Html.RadioButton
输出: <input type="radio" .. />
Html.TextArea
输出: <textarea…>…</textarea>
Html.TextBox
输出: <input type="text" … />
Html.ValidationSummary
Returns an unordered list (ul element) of validation messages that are in the ModelStateDictionary object.
返回一个在ModelStateDictionary对象中的无序列表（ul元素）的验证消息。
Html.ValidationMessage
To display an error for a particular field in the ModelState dictionary
要显示一个错误的ModelState字典中的特定字段
Html.RouteLink
To generate a URL to a specific route
要生成一个URL到一个特定的路由