Added XamlFileProjectPath to UpdateXamlMessage

src/Avalonia.DesignerSupport/DesignWindowLoader.cs

@@ -12,7 +12,7 @@ namespace Avalonia.DesignerSupport
 {
     public class DesignWindowLoader
     {
-        public static Window LoadDesignerWindow(string xaml, string assemblyPath)
+        public static Window LoadDesignerWindow(string xaml, string assemblyPath, string xamlFileProjectPath)
         {
             Window window;
             Control control;
@@ -26,9 +26,11 @@ namespace Avalonia.DesignerSupport
                 Uri baseUri = null;
                 if (assemblyPath != null)
                 {
+                    if (xamlFileProjectPath == null)
+                        xamlFileProjectPath = "/Designer/Fake.xaml";
                     //Fabricate fake Uri
                     baseUri =
-                        new Uri($"res:asm:{Path.GetFileNameWithoutExtension(assemblyPath)}/Designer/Fake.xaml");
+                        new Uri($"res:asm:{Path.GetFileNameWithoutExtension(assemblyPath)}{xamlFileProjectPath}");
                 }
 
                 var localAsm = assemblyPath != null ? Assembly.LoadFile(Path.GetFullPath(assemblyPath)) : null;

src/Avalonia.DesignerSupport/Remote/RemoteDesignerEntryPoint.cs

@@ -199,7 +199,7 @@ namespace Avalonia.DesignerSupport.Remote
                 s_currentWindow = null;
                 try
                 {
-                    s_currentWindow = DesignWindowLoader.LoadDesignerWindow(xaml.Xaml, xaml.AssemblyPath);
+                    s_currentWindow = DesignWindowLoader.LoadDesignerWindow(xaml.Xaml, xaml.AssemblyPath, xaml.XamlFileProjectPath);
                     s_transport.Send(new UpdateXamlResultMessage(){Handle = s_currentWindow.PlatformImpl?.Handle?.Handle.ToString()});
                 }
                 catch (Exception e)

src/Avalonia.Remote.Protocol/DesignMessages.cs

@@ -7,6 +7,7 @@ namespace Avalonia.Remote.Protocol.Designer
     {
         public string Xaml { get; set; }
         public string AssemblyPath { get; set; }
+        public string XamlFileProjectPath { get; set; }
     }
 
     [AvaloniaRemoteMessageGuid("B7A70093-0C5D-47FD-9261-22086D43A2E2")]
@@ -22,4 +23,4 @@ namespace Avalonia.Remote.Protocol.Designer
         public string SessionId { get; set; }
     }
     
-}
+}