AspNetCore在TagHelper中获取wwwroot的路径

Question

我尝试创建一个TagHelper来检查图像是否存在,如果不存在,则替换默认图像的路径.

不幸的是我在标签帮助器中映射"〜"符号时遇到了问题.

例如.我的图像的src包含"〜\ images\image1.png".现在我想检查这个文件的存在,如果没有用标签的属性替换另一个文件.我被困在将"〜"映射到我的应用程序的wwwroot.

这就是我的实际情况:

[HtmlTargetElement("img", TagStructure = TagStructure.WithoutEndTag)]
public class ImageTagHelper : TagHelper
{
    public ImageTagHelper(IHostingEnvironment environment)
    {
        this._env = environment;
    }

    private IHostingEnvironment _env;

    public string DefaultImageSrc { get; set; }

    public override void Process(TagHelperContext context, TagHelperOutput output)
    {
    //    urlHelper.ActionContext.HttpContext.
    //var env = ViewContext.HttpContext.ApplicationServices.GetService(typeof(IHostingEnvironment)) as IHostingEnvironment;

        string imgPath = context.AllAttributes["src"].Value.ToString();

        if (!File.Exists(_env.WebRootPath + imgPath)) {
            output.Attributes.SetAttribute("src", _env.WebRootPath + DefaultImageSrc);
        }
    }

}

Answer 1

您应该对IUrlHelperFactor和IActionContextAccessor采用构造函数依赖,这将使您能够获得可以使用"〜/"语法从wwwroot解析URL的IUrlHelper

public ImageTagHelper(
    IUrlHelperFactory urlHelperFactory,
    IActionContextAccessor actionContextAccesor,)
{
    this.urlHelperFactory = urlHelperFactory;
    this.actionContextAccesor = actionContextAccesor;
}

private IUrlHelperFactory urlHelperFactory;
private IActionContextAccessor actionContextAccesor;

public override void Process(TagHelperContext context, TagHelperOutput output)
{
    var urlHelper = urlHelperFactory.GetUrlHelper(actionContextAccesor.ActionContext);
    var myUrl = urlHelper.Content("~/somefilebelowwwwroot");
    ...
}

你可以看到我在我的PagerTagHelper中这样做

Answer 2

它需要在 Startup.cs 的 ConfigureServices 方法中添加

您需要添加以下几行：

        services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>();
        services.AddSingleton<IActionContextAccessor, ActionContextAccessor>();

然后这有效：

   [HtmlTargetElement("img", TagStructure = TagStructure.WithoutEndTag)]
    public class ImageTagHelper : TagHelper
    {
        public ImageTagHelper(IUrlHelperFactory urlHelperFactory,
                              IActionContextAccessor actionContextAccessor,
                              IHostingEnvironment environment)
        {
            _urlHelperFactory = urlHelperFactory;
            _actionContextAccessor = actionContextAccessor;
            _env = environment;
        }

        private IUrlHelperFactory _urlHelperFactory;
        private IActionContextAccessor _actionContextAccessor;

        private IHostingEnvironment _env;

        public string DefaultImageSrc { get; set; }

        public override void Process(TagHelperContext context, TagHelperOutput output)
        {
            string imgPath = context.AllAttributes["src"].Value.ToString();

            IUrlHelper urlHelper = _urlHelperFactory.GetUrlHelper(_actionContextAccessor.ActionContext);

            if (!imgPath.StartsWith("data:"))
            {
                if (!File.Exists(_env.WebRootPath + urlHelper.Content(imgPath)))
                {
                    if (DefaultImageSrc != null)
                    {
                        output.Attributes.SetAttribute("src", urlHelper.Content(DefaultImageSrc));
                    }
                }
            }
        }

    }