asp.net-core-mvc – 确定Tag Helper中的当前路由.这可能吗？

@addTagHelper "*,Microsoft.AspNet.Mvc.TagHelpers"
@addTagHelper "*,WebApplication5"

然后,无论何时执行帮助程序,TagHelperOutput都将包含使用asp-controller和asp-action标记的默认AnchorTagHelper生成的href.

//Get url from href attribute generated by the default AnchorTagHelper
var url = output.Attributes["href"].Value.ToString();

然后,您可以将该URL与将为当前请求生成的URL进行比较：

var currentRoutUrl = this.urlHelper.Action();

Initially I tried the code below,but it does not work when using attribute routing. I can see an entry with key !__route_group in the route values and an exception ArgumentException: An item with the same key has already been added is thrown:

06003

这样做而不是比较当前请求URL是有原因的.这样,无论当前请求url是“/”还是“/ Home / Index”,在这两种情况下,您都会考虑为控制器Home和action Index激活一个链接)

我按照这个想法创建了一个标签助手：

>标签助手将用于< a>已定义属性highlight-active的元素. (这允许css类的属性是可选的,在这种情况下使用默认的活动类)：
>标记属性highlight-active从输出html中删除
> class属性与css-active-class属性合并(也从输出html中删除)

代码如下：

[HtmlTargetElement("a",Attributes = "highlight-active")]
public class RouteTagHelper : TagHelper
{
    private IActionContextAccessor actionContextAccessor;
    private IUrlHelper urlHelper;

    public RouteTagHelper(IActionContextAccessor actionContextAccessor,IUrlHelper urlHelper)
    {
        this.actionContextAccessor = actionContextAccessor;
        this.urlHelper = urlHelper;
    }

    //Optional attribute. If not defined,"active" class will be used
    [HtmlAttributeName("css-active-class")]
    public string CssClass { get; set; } = "active";

    public override void Process(TagHelperContext context,TagHelperOutput output)
    {
        //Remove marker attribute
        output.Attributes.Remove(output.Attributes["highlight-active"]);

        //Get the url from href attribute generaed in the default AnchorTagHelper
        var url = output.Attributes["href"].Value.ToString();

        //Add active css class only when current request matches the generated href
        var currentRouteUrl = this.urlHelper.Action();
        if (url == currentRouteUrl)
        {
            var linkTag = new TagBuilder("a");
            linkTag.Attributes.Add("class",this.CssClass);
            output.MergeAttributes(linkTag);
        }
    }
}

因此,您现在可以在主页/索引页面中编写以下内容：

<a class="menu" asp-controller="Home" asp-action="Index" highlight-active>Home</a>
<a class="menu" asp-controller="Home" asp-action="About" highlight-active>About</a>
<a class="menu" asp-controller="Home" asp-action="Index" highlight-active css-active-class="myActiveClass">Home with special class name</a>
<a class="menu" asp-controller="Home" asp-action="Index">Home using default tag helper</a>

其呈现方式如下(无论当前网址是/或/ Home还是/ Home / Index)：

<a class="menu active" href="/">Home</a>
<a class="menu" href="/Home/About">About</a>
<a class="menu myActiveClass" href="/">Home with special class</a>
<a class="menu" href="/">Home using default tag helper</a>

PS.当您添加一个直接指定href属性的锚点时,您可能仍需要考虑这些情况(在调用base.Process之前,您可以检测是否已经有一个href).在这种情况下,您可能还希望与当前URL进行比较(通过httpContext.Request).