解讀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" /* 這里需要首先引用TagHelper所在的命名空間 */

<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" 

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"  />
<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="https://www.gxlcms.com//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="https://www.gxlcms.com//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="https://www.gxlcms.com//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="https://www.gxlcms.com//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="https://www.gxlcms.com//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="https://www.gxlcms.com//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);

 // 刪除所有的attributes，因為路由里已經可以自動生成了
 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" >© @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)
 {
 // 如果設置了condition，并且該值為false，則不渲染該元素
 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 }"/>