解读ASP.NET 5 & MVC6系列教程（13）：TagHelper

@html.labelfor(model => model.fullname)
@html.editfor(model => model.fullname)
@html.validationmessagefor(model => model.fullname)

@addtaghelper "*, microsoft.aspnet.mvc.taghelpers" /* 这里需要首先引用taghelper所在的命名空间 */

<label asp-for="fullname" class="control-label col-md-2"></label>
<div class="col-md-10">
 <input asp-for="fullname" class="form-control" />
 <span asp-validation-for="fullname"></span>
</div>

<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 }"/>