asp.net core 自定視圖主題 實現IViewLocationExpander接口

新建ThemeViewLocationExpander.cs 實現IViewLocationExpander接口

 /// <summary>
    /// 自定視圖主題 實現IViewLocationExpander接口
    /// </summary>
    public class ThemeViewLocationExpander : IViewLocationExpander
    {
        public ThemeViewLocationExpander()
        {
        }
        /// <summary>
        /// 主題名稱
        /// /Views/+ViewLocationExpanders
        /// </summary>
        public string ThemeName { get; set; } = "Default";

        public void PopulateValues([FromServices]ViewLocationExpanderContext context)
        {
            HttpContext httpcontext = context.ActionContext.HttpContext;
            string theme = httpcontext.Request.GetTheme();
            if (theme.IsNotNullOrEmpty())
            {
                ThemeName = theme;
            }
            context.Values["theme"] = ThemeName;
        }

        /// <summary>
        /// 主題切換
        /// </summary>
        /// <param name="theme"></param>
        /// <returns></returns>
        public virtual IEnumerable<string> ExpandViewLocations(ViewLocationExpanderContext context,
                                                               IEnumerable<string> viewLocations)
        {
            string n = string.Empty;
            foreach (string item in viewLocations)
            {
                n = item.ToLower();
                if (!n.Contains("/shared"))
                {
                    n = n.Replace("{1}", $"theme/{context.Values["theme"]}/{{1}}");
                }
                yield return n;
            }

        }
    }

　添加新的ViewLocationExpanders

 public class Startup{
  public virtual void ConfigureServices(IServiceCollection services)
        {
services.AddMvc().AddRazorOptions(option =>
    {
        option.ViewLocationExpanders.Clear();
        option.ViewLocationExpanders.Add(new ThemeViewLocationExpander());
    })
    }
}