asp. Net core theme Middleware

asp.net core Custom view engine in , Inherited interface IViewLocationExpander

public class ThemeViewLocationExpander : IViewLocationExpander
    {
    
        public const string ThemeKey = "Theme";
        public void PopulateValues(ViewLocationExpanderContext context)
        {
    
            string theme = context.ActionContext.HttpContext.Items[ThemeKey].ToString();
            context.Values[ThemeKey] = theme;
        }
        public IEnumerable<string> ExpandViewLocations(ViewLocationExpanderContext context, IEnumerable<string> viewLocations)
        {
    
            string theme;

            if (context.Values.TryGetValue(ThemeKey, out theme))
            {
    
                viewLocations = new[] 
                {
    
                    $"/Themes/{
      theme}/Views/{
     {1}}/{
     {0}}.cshtml",
                    $"/Themes/{
      theme}/Views/Shared/{
     {0}}.cshtml",
                    $"/Themes/{
      theme}/Areas/{
     {2}}/Views/{
     {1}}/{
     {0}}.cshtml",
                    $"/Themes/{
      theme}/Areas/{
     {2}}/Views/Shared/{
     {0}}.cshtml",
                }
                .Concat(viewLocations);
            }
            return viewLocations;
        }
    }

New middleware ThemeMiddleware

public class ThemeMiddleware
    {
    
        private readonly RequestDelegate _next;
        public IConfiguration _configuration;
        public ThemeMiddleware(RequestDelegate next, IConfiguration configuration)
        {
    
            _next = next;
            _configuration = configuration;
        }
        public Task Invoke(HttpContext context)
        {
    
            var folder = _configuration.GetSection("theme").Value;
            context.Request.HttpContext.Items[ThemeViewLocationExpander.ThemeKey] = folder ?? "Default";
            return _next(context);
        }
    }

Middleware extensions

public static class MiddlewareExtensions
{
    
    /// <summary>
    ///  Enable Theme middleware 
    /// </summary>
    /// <param name="builder"></param>
    /// <returns></returns>
    public static IApplicationBuilder UseTheme(this IApplicationBuilder builder)
    {
    
        return builder.UseMiddleware<ThemeMiddleware>();
    }
}

Middleware service extensions

public static class ServiceCollectionExtensions
    {
    
        /// <summary>
        ///  add to Theme service 
        /// </summary>
        /// <param name="services"></param>
        /// <returns></returns>
        public static IServiceCollection AddTheme(this IServiceCollection services)
        {
    
            return services.Configure<RazorViewEngineOptions>(options => {
    
                options.ViewLocationExpanders.Add(new ThemeViewLocationExpander());
            });
        }
    }

Use :

public void ConfigureServices(IServiceCollection services)
        {
    
            services.AddTheme(); // add to Theme service 
            services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1);
        }


public void Configure(IApplicationBuilder app, IHostingEnvironment env)
        {
    
          

            app.UseTheme();// Enable theme middleware 
            app.UseMvcWithDefaultRoute();
}

---

C# - stay MVC Use in IViewLocationExpander

I want to render from a custom location View , So I have achieved
Class IViewLocationExpander Interface (interface). I am already in Startup Class is registered with the same class , As shown below .

Startup class

public void ConfigureServices(IServiceCollection services)
{
    
    … 
    //Render view from custom location.
    services.Configure<RazorViewEngineOptions>(options =>
    {
    
        options.ViewLocationExpanders.Add(new CustomViewLocationExpander());
    });
    … 
}

CustomViewLocationExpander class

public class CustomViewLocationExpander : IViewLocationExpander
{
    
    public IEnumerable<string> ExpandViewLocations(ViewLocationExpanderContext context, IEnumerable<string> viewLocations)
    {
    

        var session = context.ActionContext.HttpContext.RequestServices.GetRequiredService<SessionServices>();
        string folderName = session.GetSession<string>("ApplicationType");

        viewLocations = viewLocations.Select(f => f.Replace("/Views/", "/" + folderName + "/"));


        return viewLocations;
    }

    public void PopulateValues(ViewLocationExpanderContext context)
    {
    

    }
}

Last , Of my application View Is organized as follows :

My question : If I start from the following URL from Views/Login Folder Access ViewsFrontend View :

http://localhost:56739/trainee/Login/myclientname 

But then immediately put... In the browser URL Change to :

http://localhost:56739/admin/Login/myclientname

under these circumstances , Even now it should now reference ViewsFrontend Folder , It still references ViewsBackend Folder , Because in order to trainee At the beginning URL You should quote ViewsFrontend Folder , And then admin At the beginning URL You should quote ViewsBackend Folder .

Besides , Change... In the browser URL after , It just calls PopulateValues() Method , Instead of calling ExpandViewLocations() Method .

How do I reconfigure ​​ This class makes it available to other folders ？

The best answer

PopulateValues Is a method for specifying parameters , Your View The lookup will vary according to each request . Because it is not filled , therefore View The engine will use the cached value from the previous request .

To solve this problem , Please send your ApplicationType Variable added to PopulateValues() In the method , And as long as the value changes , You should call ExpandValues() Method :

public class CustomViewLocationExpander : IViewLocationExpander
{
    
    public IEnumerable<string> ExpandViewLocations(ViewLocationExpanderContext context, IEnumerable<string> viewLocations)
    {
    
        string folderName = context.Values["ApplicationType"];
        viewLocations = viewLocations.Select(f => f.Replace("/Views/", "/" + folderName + "/"));

        return viewLocations;
    }

    public void PopulateValues(ViewLocationExpanderContext context)
    {
    
        var session = context.ActionContext.HttpContext.RequestServices.GetRequiredService<SessionServices>();
        string applicationType = session.GetSession<string>("ApplicationType");
        context.Values["ApplicationType"] = applicationType;
    }
}