MVC---Help Methods

一. 创建自定义Help Method

@model string
@{
    Layout = null;
}




    
    


    

        Here are the fruits:
        @foreach (string str in (string[])ViewBag.Fruits)
        {
            @str 
        }
    
    

        Here are the cities:
        @foreach (string str in (string[])ViewBag.Cities)
        {
            @str 
        }
    
    

        Here is the message:
        
@Model
    

1.1 创建内联(Inline)的Help Method

@model string
@{
    Layout = null;
}

@helper ListArrayItems(string[] items)
{
    foreach (string str in items)
    {
        @str 
    }
}




    
    


    

        Here are the fruits:
        @ListArrayItems(ViewBag.Fruits)
    
    

        Here are the cities:
        @ListArrayItems(ViewBag.Cities)
    
    

        Here is the message:
        
@Model
    

内联Help Method看上去是一个方法，但是没有返回值。

1.2 创建外部的Help Method

    public static class CustomHelpers
    {
        public static MvcHtmlString ListArrayItems(this HtmlHelper html, string[] list)
        {
            TagBuilder tag = new TagBuilder("ul");
            foreach (string str in list)
            {
                TagBuilder itemTag = new TagBuilder("li");
                itemTag.SetInnerText(str);
                tag.InnerHtml += itemTag.ToString();
            }
            return MvcHtmlString.Create(tag.ToString());
        }
    }

this关键字说明定义的是一个扩展方法，HtmlHelper类型的实例能够提供很多内容，如Controller，View，RouteData等。
TagBuilder常用的成员有：
InnerHtml
SetInnerText(string)
AddCssClass(string)
MergeAttribute(string, string, bool)

使用自定义的外部Help Method：

@model string
@using HelperMethods.Infrastructure
@{
    Layout = null;
}




    
    


    

        Here are the fruits:@Html.ListArrayItems((string[])ViewBag.Fruits)
    
    

        Here are the cities:@Html.ListArrayItems((string[])ViewBag.Cities)
    
    

        Here is the message:
        
@Model
    

1.3 管理HelpMethods中的字符串编码
处于安全性考虑，需要防止数据被浏览器解释成标记。
必须对Help Methods的内容进行编码。
解决方式是使用Encode方法：

        public static MvcHtmlString DisplayMessage(this HtmlHelper html, string msg)
        {
            // msg值为： This is an Html element:
            string encodeMessage = html.Encode(msg);
            string result = string.Format("This is th message:
{0}
", encodeMessage);
            return new MvcHtmlString(result);
        }

1.4 使用内建的Form Help Methods
1.4.1 创建Form元素
标准的表单如下：

   

        

            PersonId
            
        
        

            First Name
            
        
        

            Last Name
            
        
        
    

使用Help Methods：

@using (Html.BeginForm())
{
    

        PersonId
        
    
    

        First Name
        
    
    

        Last Name
        
    
    
}

BeginForm有多个重载方法：

@using (Html.BeginForm("CreatePerson", "Home", 
    new { id = "MyIdValue" }, FormMethod.Post, 
    new { @class = "personClass", data_fromType = "person" }))
{
    

        PersonId
        
    
    

        First Name
        
    
    

        Last Name
        
    
    
}

调用上述BeginForm所产生的HTML的form标签为：

1.4.2 指定Form使用的路由
首先在RouteConfig中加入一条路由：

routes.MapRoute(name: "FormRoute", url: "app/forms/{controller}/{action}");

如果需要确保使用特定的一条路由：

@using (Html.BeginRouteForm("FormRoute", 
new { }, 
FormMethod.Post, 
new { @class = "personClass", data_formType = "person" }))
{
}

产生的form标签为：

1.4.3 使用Input Helper

Input Html Helper.png

@using (Html.BeginRouteForm("FormRoute", new { }, FormMethod.Post, new { @class = "personClass", data_formType = "person" }))
{
    

        PersonId
        @**@
        @Html.TextBox("personId", @Model.PersonId)
    
    

        First Name
        @Html.TextBox("firstName", @Model.FirstName)
    
    

        Last Name
        @**@
        @Html.TextBox("lastName", @Model.LastName)
    
    
}

上述方法需要保证第一个参数匹配第二个参数。上图中的所有input Helper都对应一个强类型的Helper。

强类型Input Html Helper.png

@using (Html.BeginRouteForm("FormRoute", new { }, FormMethod.Post, new { @class = "personClass", data_formType = "person" }))
{
    

        PersonId
        @**@
        @*@Html.TextBox("personId", @Model.PersonId)*@
        @Html.TextBoxFor(m => m.PersonId)
    
    

        First Name
        @*@Html.TextBox("firstName", @Model.FirstName)*@
        @Html.TextBoxFor(m => m.FirstName)
    
    

        Last Name
        @**@
        @*@Html.TextBox("lastName", @Model.LastName)*@
        @Html.TextBoxFor(m => m.LastName)
    
    
}

1.4.4 创建Select元素

Select Html Helper.png