解读ASP.NET 5 & MVC6系列教程（13）：TagHelper

link rel="stylesheet" 
href="//ajax.aspnetcdn.com/ajax/bootstrap-touch-carousel/0.8.0/css/bootstrap-touch-carousel.css"
asp-fallback-href="~/lib/bootstrap-touch-carousel/css/bootstrap-touch-carousel.css"
asp-fallback-test-class="carousel-caption" 
asp-fallback-test-property="display" 
asp-fallback-test-value="none" />

link rel="stylesheet" href="//ajax.aspnetcdn.com/ajax/bootstrap-touch-carousel/0.8.0/css/bootstrap-touch-carousel.css" />
meta name="x-stylesheet-fallback-test" class="carousel-caption" />
script>
 !function (a, b, c) {
  var d, e = document,
   f = e.getElementsByTagName("SCRIPT"),
   g = f[f.length - 1].previousElementSibling,
   h = e.defaultView  e.defaultView.getComputedStyle ? e.defaultView.getComputedStyle(g) : g.currentStyle;

  if (h  h[a] !== b) {
   for (d = 0; d  c.length; d++) {
    e.write('link rel="stylesheet" href="' + c[d] + '"/>')
   }
  }
 }("display", "none", ["\/lib\/bootstrap-touch-carousel\/css\/bootstrap-touch-carousel.css"]);
/script>

script src="//ajax.aspnetcdn.com/ajax/jquery/jquery-1.10.2.min.js"
 asp-fallback-src="~/lib/jquery/jquery.min.js"
 asp-fallback-test="window.jQuery">
/script>

script src="//ajax.aspnetcdn.com/ajax/jquery/jquery-1.10.2.min.js">
/script>
script>(window.jQuery||document.write("script src=\"\/lib\/jquery\/jquery.min.js\">\/script>"));/script>

environment names="Development">
 script src="~/lib/jquery/jquery.js">/script>
 script src="~/lib/bootstrap/js/bootstrap.js">/script>
 script src="~/lib/hammer.js/hammer.js">/script>
 script src="~/lib/bootstrap-touch-carousel/js/bootstrap-touch-carousel.js">/script>
/environment>
environment names="Staging,Production">
 script src="//ajax.aspnetcdn.com/ajax/jquery/jquery-1.10.2.min.js"
   asp-fallback-src="~/lib/jquery/jquery.min.js"
   asp-fallback-test="window.jQuery">
 /script>
 script src="//ajax.aspnetcdn.com/ajax/bootstrap/3.0.0/bootstrap.min.js"
   asp-fallback-src="~/lib/bootstrap/js/bootstrap.min.js"
   asp-fallback-test="window.jQuery">
 /script>
 script src="//ajax.aspnetcdn.com/ajax/hammer.js/2.0.4/hammer.min.js"
   asp-fallback-src="~/lib/hammer.js/hammer.js"
   asp-fallback-test="window.Hammer">
 /script>
 script src="//ajax.aspnetcdn.com/ajax/bootstrap-touch-carousel/0.8.0/js/bootstrap-touch-carousel.js"
   asp-fallback-src="~/lib/bootstrap-touch-carousel/js/bootstrap-touch-carousel.js"
   asp-fallback-test="window.Zepto">
 /script>
/environment>

public interface ITagHelper
{
 int Order { get; }
 Task ProcessAsync(TagHelperContext context, TagHelperOutput output);
}

public class ATagHelper : TagHelper
{
 [Activate]
 public IUrlHelper UrlHelper { get; set; }

 public string Controller { get; set; }

 public string Action { get; set; }

 public override void Process(TagHelperContext context, TagHelperOutput output)
 {
  if (Controller != null  Action != null)
  {
   var methodParameters = output.Attributes.ToDictionary(attribute => attribute.Key,
                 attribute => (object)attribute.Value);

   // 删除所有的attributes，因为路由里已经可以自动生成了
   output.Attributes.Clear();

   output.Attributes["href"] = UrlHelper.Action(Action, Controller, methodParameters);

   output.PreContent.SetContent("My ");
  }
 }
}

[TargetElement("p")]
public class AutoLinkerTagHelper : TagHelper
{
 public override async Task ProcessAsync(TagHelperContext context, TagHelperOutput output)
 {
  var childContent = await context.GetChildContentAsync();

  // Find Urls in the content and replace them with their anchor tag equivalent.
  output.Content.SetContent(Regex.Replace(
   childContent.GetContent(),
   @"\b(?:https?://|www\.)(\S+)\b",
   "strong>a target=\"_blank\" href=\"http://$0\">$0/a>/strong>"));
 }
}

p condition="Model.Approved" >copy; @Model.CopyrightYear - My ASP.NET Application/p>

[TargetElement("div")]
[TargetElement("style")]
[TargetElement("p")]
public class ConditionTagHelper : TagHelper
{
 public bool? Condition { get; set; }

 public override void Process(TagHelperContext context, TagHelperOutput output)
 {
  // 如果设置了condition，并且该值为false，则不渲染该元素
  if (Condition.HasValue  !Condition.Value)
  {
   output.SuppressOutput();
  }
 }
}

public class WebsiteInformationTagHelper : TagHelper
{
 public WebsiteContext Info { get; set; }

 public override void Process(TagHelperContext context, TagHelperOutput output)
 {
  output.TagName = "section";
  output.PostContent.SetContent(string.Format(
   "p>strong>Version:/strong> {0}/p>" + Environment.NewLine +
   "p>strong>Copyright Year:/strong> {1}/p>" + Environment.NewLine +
   "p>strong>Approved:/strong> {2}/p>" + Environment.NewLine +
   "p>strong>Number of tags to show:/strong> {3}/p>" + Environment.NewLine,
   Info.Version.ToString(),
   Info.CopyrightYear.ToString(),
   Info.Approved.ToString(),
   Info.TagsToShow.ToString()));
  output.SelfClosing = false;
 }
}

website-information info="new WebsiteContext {
        Version = new Version(1, 1),
        CopyrightYear = 1990,
        Approved = true,
        TagsToShow = 30 }"/>