asp.net-core-mvc - 确定标记帮助程序中的当前路线。这可能吗？

Question

在 ASP.NET MVC 6 项目中，我有以下内容:

[Route("help/how-it-works")]
public IActionResult HowItWorks() {
   return View();
}

我想创建一个标签助手，如下所示:

<a class="menu" asp-controller="Help" asp-action="HowItWorks" route-is="help/how-it-works" css-class="active">How it works</a>

因此，route-is 标签助手会检查当前路由是否为“help/how-it-works”...如果是，则将“active”添加到 A 标签的 css 类中。

所以我开始创建一个标签助手:

[TargetElement("a", Attributes = "route-is, css-class")]
public class RouteTagHelper : TagHelper
{

public override void Process(TagHelperContext context, TagHelperOutput output)
{

    String routeIs = context.AllAttributes["route-is"].ToString();

    String cssClass = context.AllAttributes["css-class"].ToString();

    if (String.IsNullOrWhiteSpace(cssClass))
        cssClass = "active";

    ViewContext.RouteData.Values.Keys;

}
}// Process

我的问题是如何确定当前路由是否为“help/how-it-works”以及是否将 Css 类添加到 A 标记而不更改其他任何内容。

有人知道如何做到这一点吗？

更新1

解决了使用属性路由时出现重复值的问题，并添加了 Daniel J.G. 提出的替代方法

[TargetElement("a", Attributes = RouteIsName)]
[TargetElement("a", Attributes = RouteHasName)]
public class ActiveRouteTagHelper : TagHelper
{
    private const String RouteIsName = "route-is";
    private const String RouteHasName = "route-has";
    private const String RouteCssName = "route-css";

    private IActionContextAccessor _actionContextAccessor;
    private IUrlHelper _urlHelper;

    [HtmlAttributeName(RouteCssName)]
    public String RouteCss { get; set; } = "active";

    [HtmlAttributeName(RouteHasName)]
    public String RouteHas { get; set; }

    [HtmlAttributeName(RouteIsName)]
    public String RouteIs { get; set; }


    public ActiveRouteTagHelper(IActionContextAccessor actionContextAccessor, IUrlHelper urlHelper)
    {

        _actionContextAccessor = actionContextAccessor;
        _urlHelper = urlHelper;

    } // ActiveRouteTagHelper


    public override void Process(TagHelperContext context, TagHelperOutput output)
    {

        IDictionary<String, Object> values = _actionContextAccessor.ActionContext.RouteData.Values;

        String route = _urlHelper.RouteUrl(values.Distinct()).ToLowerInvariant();

        Boolean match = false;

        if (!String.IsNullOrWhiteSpace(RouteIs))
        {

            match = route == RouteIs;

        } else {        

            if (RouteHas != null) {

                String[] keys = RouteHas.Split(',');

            if (keys.Length > 0) 
                match = keys.All(x => route.Contains(x.ToLowerInvariant()));

            }
        }

        if (match)
        {
            TagBuilder link = new TagBuilder("a");
            link.AddCssClass(RouteCss);
            output.MergeAttributes(link);
        }

    } // Process

} // ActiveRouteTagHelper

Answer 1

您可以利用您定位相同元素 <a> 的事实比默认的 MVC AnchorTagHelper 。您只需确保在 _ViewImports.cshtml 中的默认助手之后添加助手即可:

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

然后每当你的助手被执行时，TagHelperOutput已经包含默认 AnchorTagHelper 生成的 href使用asp-controller和asp-action标签。

//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:

var currentRouteUrl = this.urlHelper.RouteUrl(
                               this.actionContextAccessor.ActionContext.RouteData.Values);

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，您都会考虑激活 Controller Home 和操作 Index 的链接)

我按照这个想法创建了一个标签助手:

• 标签助手将用于 <a>具有属性 highlight-active 的元素定义的。 (这允许 css 类的属性是可选的，在这种情况下使用默认的 active 类):

• 标记属性 highlight-active从输出 html 中删除

• 类属性与 css-active-class 合并属性(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);
        }
    }
}

现在您可以在主页/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>

呈现如下(无论当前 url 是 / 或 /Home 或 /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。当您添加直接指定 href 的 anchor 时，您可能仍然需要考虑这种情况。属性(您可以在调用 base.Process 之前检查是否已经有 href )。在这种情况下，您可能还想与当前 url 进行比较(通过 httpContext.Request)。