Created simple theme manager.

src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic/AbpAspNetCoreMvcUIBasicThemeModule.cs

@@ -2,6 +2,7 @@
 using Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic.Toolbars;
 using Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared;
 using Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared.Toolbars;
+using Volo.Abp.AspNetCore.Mvc.UI.Theming;
 using Volo.Abp.Modularity;
 using Volo.Abp.VirtualFileSystem;
 
@@ -14,6 +15,11 @@ namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic
     {
         public override void ConfigureServices(IServiceCollection services)
         {
+            services.Configure<ThemingOptions>(options =>
+            {
+                options.Themes.Add<BasicTheme>();
+            });
+
             services.Configure<VirtualFileSystemOptions>(options =>
             {
                 options.FileSets.AddEmbedded<AbpAspNetCoreMvcUiBasicThemeModule>("Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic");
@@ -23,7 +29,7 @@ namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic
             {
                 options.Contributors.Add(new BasicThemeMainTopToolbarContributor());
             });
-
+            
             services.AddAssemblyOf<AbpAspNetCoreMvcUiBasicThemeModule>();
         }
     }

src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic/BasicTheme.cs

@@ -0,0 +1,15 @@
+using Volo.Abp.AspNetCore.Mvc.UI.Theming;
+using Volo.Abp.DependencyInjection;
+
+namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic
+{
+    public class BasicTheme : ITheme, ITransientDependency
+    {
+        public string DefaultLayout => "~/Views/Shared/_AppLayout.cshtml";
+
+        public string GetLayoutOrNull(string name)
+        {
+            return DefaultLayout;
+        }
+    }
+}

src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic/Pages/_ViewStart.cshtml

@@ -1,3 +1,6 @@
-@{
-    Layout = "~/Views/Shared/_AppLayout.cshtml";
-}
+@using Volo.Abp.AspNetCore.Mvc.UI.Theming
+@inject IThemeManager ThemeManager
+@{
+    //TODO: Move this to a lower layer... to Shared?
+    Layout = ThemeManager.CurrentTheme.DefaultLayout;
+}

src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic/Toolbars/BasicThemeMainTopToolbarContributor.cs

@@ -14,6 +14,11 @@ namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Basic.Toolbars
                 return Task.CompletedTask;
             }
 
+            if (!(context.Theme is BasicTheme))
+            {
+                return Task.CompletedTask;
+            }
+
             context.Toolbar.Items.Add(new ToolbarItem(typeof(LanguageSwitchViewComponent)));
             context.Toolbar.Items.Add(new ToolbarItem(typeof(UserMenuViewComponent)));
 

src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared/Toolbars/IToolbarConfigurationContext.cs

@@ -1,9 +1,12 @@
-using Volo.Abp.DependencyInjection;
+using Volo.Abp.AspNetCore.Mvc.UI.Theming;
+using Volo.Abp.DependencyInjection;
 
 namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared.Toolbars
 {
     public interface IToolbarConfigurationContext : IServiceProviderAccessor
     {
+        ITheme Theme { get; }
+
         Toolbar Toolbar { get; }
     }
 }

src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared/Toolbars/ToolbarConfigurationContext.cs

@@ -1,15 +1,19 @@
 using System;
+using Volo.Abp.AspNetCore.Mvc.UI.Theming;
 
 namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared.Toolbars
 {
     public class ToolbarConfigurationContext : IToolbarConfigurationContext
     {
+        public ITheme Theme { get; }
+
         public Toolbar Toolbar { get; }
 
         public IServiceProvider ServiceProvider { get; }
         
-        public ToolbarConfigurationContext(Toolbar toolbar, IServiceProvider serviceProvider)
+        public ToolbarConfigurationContext(ITheme currentTheme, Toolbar toolbar, IServiceProvider serviceProvider)
         {
+            Theme = currentTheme;
             Toolbar = toolbar;
             ServiceProvider = serviceProvider;
         }

src/Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared/Toolbars/ToolbarManager.cs

@@ -2,17 +2,23 @@
 using System.Threading.Tasks;
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Options;
+using Volo.Abp.AspNetCore.Mvc.UI.Theming;
 using Volo.Abp.DependencyInjection;
 
 namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared.Toolbars
 {
     public class ToolbarManager : IToolbarManager, ITransientDependency
     {
+        protected IThemeManager ThemeManager { get; }
         protected ToolbarOptions Options { get; }
         protected IServiceProvider ServiceProvider { get; }
 
-        public ToolbarManager(IOptions<ToolbarOptions> options, IServiceProvider serviceProvider)
+        public ToolbarManager(
+            IOptions<ToolbarOptions> options, 
+            IServiceProvider serviceProvider,
+            IThemeManager themeManager)
         {
+            ThemeManager = themeManager;
             ServiceProvider = serviceProvider;
             Options = options.Value;
         }
@@ -23,7 +29,7 @@ namespace Volo.Abp.AspNetCore.Mvc.UI.Theme.Shared.Toolbars
 
             using (var scope = ServiceProvider.CreateScope())
             {
-                var context = new ToolbarConfigurationContext(menu, scope.ServiceProvider);
+                var context = new ToolbarConfigurationContext(ThemeManager.CurrentTheme, menu, scope.ServiceProvider);
 
                 foreach (var contributor in Options.Contributors)
                 {

src/Volo.Abp.AspNetCore.Mvc.UI/UI/Theming/DefaultThemeManager.cs

@@ -0,0 +1,54 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
+using Volo.Abp.DependencyInjection;
+
+namespace Volo.Abp.AspNetCore.Mvc.UI.Theming
+{
+    public class DefaultThemeManager : IThemeManager, ITransientDependency, IServiceProviderAccessor
+    {
+        public IServiceProvider ServiceProvider { get; }
+
+        public ITheme CurrentTheme => GetCurrentTheme();
+
+        protected ThemingOptions Options { get; }
+
+        protected Lazy<List<ITheme>> Themes { get; }
+
+        private readonly IHttpContextAccessor _httpContextAccessor;
+
+        public DefaultThemeManager(
+            IOptions<ThemingOptions> options, 
+            IServiceProvider serviceProvider,
+            IHttpContextAccessor httpContextAccessor)
+        {
+            _httpContextAccessor = httpContextAccessor;
+            ServiceProvider = serviceProvider;
+            Options = options.Value;
+            Themes = new Lazy<List<ITheme>>(CreateThemeList, true);
+        }
+
+        protected virtual ITheme GetCurrentTheme()
+        {
+            return Themes.Value.First();
+            ////TODO: Temporary code!
+
+            //var currentTheme = _httpContextAccessor.HttpContext.Items["_AbpCurrentTheme"] as ITheme;
+            //if (currentTheme != null)
+            //{
+            //    return currentTheme;
+            //}
+
+            //_httpContextAccessor.HttpContext.Items["_AbpCurrentTheme"] = currentTheme = RandomHelper.GetRandomOf(Themes.Value.ToArray());
+            //return currentTheme;
+        }
+
+        protected virtual List<ITheme> CreateThemeList()
+        {
+            return Options.Themes.Select(t => (ITheme) ServiceProvider.GetRequiredService(t)).ToList();
+        }
+    }
+}

src/Volo.Abp.AspNetCore.Mvc.UI/UI/Theming/ITheme.cs

@@ -0,0 +1,9 @@
+namespace Volo.Abp.AspNetCore.Mvc.UI.Theming
+{
+    public interface ITheme
+    {
+        string DefaultLayout { get; }
+
+        string GetLayoutOrNull(string name);
+    }
+}

src/Volo.Abp.AspNetCore.Mvc.UI/UI/Theming/IThemeManager.cs

@@ -0,0 +1,7 @@
+namespace Volo.Abp.AspNetCore.Mvc.UI.Theming
+{
+    public interface IThemeManager
+    {
+        ITheme CurrentTheme { get; }
+    }
+}

src/Volo.Abp.AspNetCore.Mvc.UI/UI/Theming/ThemingOptions.cs

@@ -0,0 +1,14 @@
+using Volo.Abp.Collections;
+
+namespace Volo.Abp.AspNetCore.Mvc.UI.Theming
+{
+    public class ThemingOptions
+    {
+        public TypeList<ITheme> Themes { get; }
+
+        public ThemingOptions()
+        {
+            Themes = new TypeList<ITheme>();
+        }
+    }
+}