Fix: Fixed issue where custom theme was not applied on launch (#10587)

Reload resources when applying theme

Author: gave92

src/Files.App/Helpers/ExternalResourcesHelper.cs

@@ -97,6 +97,7 @@ public async Task<bool> TryLoadThemeAsync(AppTheme theme)
 					{
 						Themes.Add(theme);
 					}
+					ForceReloadResourceFile();
 					return true;
 				}
 				return false;
@@ -108,6 +109,22 @@ public async Task<bool> TryLoadThemeAsync(AppTheme theme)
 			}
 		}
 
+		/// <summary>
+		/// Forces the application to use the correct resource styles
+		/// </summary>
+		private void ForceReloadResourceFile()
+		{
+			// Get the index of the current theme
+			var selTheme = ThemeHelper.RootTheme;
+
+			// Toggle between the themes to force the controls to use the new resource styles
+			ThemeHelper.RootTheme = ElementTheme.Dark;
+			ThemeHelper.RootTheme = ElementTheme.Light;
+
+			// Restore the theme to the correct theme
+			ThemeHelper.RootTheme = selTheme;
+		}
+
 		public async Task<ResourceDictionary> TryLoadResourceDictionary(AppTheme theme)
 		{
 			StorageFile file;