Initialize the theme in ThemeService from RadzenTheme.

Author: akorchev

Radzen.Blazor/ThemeService.cs

@@ -1,3 +1,5 @@
+using Microsoft.AspNetCore.Components;
+using Microsoft.Extensions.DependencyInjection;
 using Microsoft.JSInterop;
 using System;
 using System.Collections;
@@ -367,13 +369,31 @@ public static class Themes
     /// <summary>
     /// Service for theme registration and management.
     /// </summary>
-    public class ThemeService(IJSRuntime jsRuntime)
+    public class ThemeService(IJSRuntime jsRuntime, IServiceProvider serviceProvider)
     {
 
+        private string theme;
         /// <summary>
         /// Gets the current theme.
         /// </summary>
-        public string Theme { get; private set; }
+        public string Theme
+        {
+            get
+            {
+                if (theme == null)
+                {
+                    var persistentComponentState = serviceProvider.GetService<PersistentComponentState>();
+
+                    if (persistentComponentState?.TryTakeFromJson(nameof(Theme), out string persistedTheme) == true)
+                    {
+                        theme = persistedTheme;
+                    }
+                }
+                return theme;
+            }
+
+            private set => theme = value;
+        }
 
         /// <summary>
         /// Specify if the theme colors should meet WCAG contrast requirements.

RadzenBlazorDemos/Pages/ThemeServicePage.razor

@@ -32,6 +32,9 @@ The Radzen.Blazor library provides a built-in service that persists the current
 
     [Inject]
     private ThemeService ThemeService { get; set; }
+    
+    [Inject]
+    private IOptions<CookieThemeServiceOptions> Options { get; set; }
 
     protected override void OnInitialized()
     {
@@ -45,6 +48,10 @@ The Radzen.Blazor library provides a built-in service that persists the current
             {
                 ThemeService.SetTheme(theme, false);
             }
+            else
+            {
+                HttpContext.Response.Cookies.Append("MyApplicationTheme", "material" , new CookieOptions { Secure = Options.Value.IsSecure, Expires = DateTimeOffset.Now.Add(Options.Value.Duration) });    
+            }
         }
     }
 }