.axaml

packages/Avalonia/Avalonia.csproj

@@ -41,6 +41,10 @@
       <Pack>true</Pack>
       <PackagePath>build\</PackagePath>
     </Content>
+    <Content Include="AvaloniaItemSchema.xaml">
+      <Pack>true</Pack>
+      <PackagePath>build\</PackagePath>
+    </Content>
   </ItemGroup>
   <Import Project="..\..\build\SharedVersion.props" />
   <Import Project="..\..\build\NetFX.props" />

packages/Avalonia/AvaloniaBuildTasks.props

@@ -1,3 +1,12 @@
 <Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-
+  <ItemGroup>
+    <AvailableItemName Include="AvaloniaXaml" />
+    <PropertyPageSchema Include="$(MSBuildThisFileDirectory)AvaloniaItemSchema.xaml" />
+    <AvaloniaXaml Include="**\*.axaml" />
+    <AvaloniaXaml Include="**\*.paml" />
+    <Compile Update="**\*.paml.cs">
+      <DependentUpon>%(Filename)</DependentUpon>
+      <SubType>Code</SubType>
+    </Compile>
+  </ItemGroup>
 </Project>

packages/Avalonia/AvaloniaBuildTasks.targets

@@ -31,9 +31,12 @@
   
   <Target Name="GenerateAvaloniaResources" 
           BeforeTargets="CoreCompile;CoreResGen"
-          Inputs="@(AvaloniaResource);$(MSBuildAllProjects)"
+          Inputs="@(AvaloniaResource);@(AvaloniaXaml);$(MSBuildAllProjects)"
           Outputs="$(AvaloniaResourcesTemporaryFilePath)"
-          DependsOnTargets="$(BuildAvaloniaResourcesDependsOn)">
+	  DependsOnTargets="$(BuildAvaloniaResourcesDependsOn)">
+    <ItemGroup>
+        <AvaloniaResource Include="@(AvaloniaXaml)"/>
+    </ItemGroup>
     <GenerateAvaloniaResourcesTask
       Condition="'$(_AvaloniaUseExternalMSBuild)' != 'true'"
       Output="$(AvaloniaResourcesTemporaryFilePath)"

packages/Avalonia/AvaloniaItemSchema.xaml

@@ -0,0 +1,13 @@
+<ProjectSchemaDefinitions xmlns="http://schemas.microsoft.com/build/2009/properties">
+    <ContentType
+        Name="AvaloniaXaml"
+        DisplayName="Avalonia XAML"
+        ItemType="AvaloniaXaml">
+      <NameValuePair Name="DependentFileExtensions" Value=".cs" />
+      <NameValuePair Name="DefaultMetadata_SubType" Value="Designer" />
+    </ContentType>
+
+    <ItemType Name="AvaloniaXaml" DisplayName="Avalonia XAML" />
+    <FileExtension Name=".axaml" ContentType="AvaloniaXaml" />
+    <FileExtension Name=".paml" ContentType="AvaloniaXaml" />
+</ProjectSchemaDefinitions>

src/Avalonia.Build.Tasks/GenerateAvaloniaResourcesTask.cs

@@ -107,7 +107,7 @@ namespace Avalonia.Build.Tasks
             
             foreach (var s in sources.ToList())
             {
-                if (s.Path.ToLowerInvariant().EndsWith(".xaml") || s.Path.ToLowerInvariant().EndsWith(".paml"))
+                if (s.Path.ToLowerInvariant().EndsWith(".xaml") || s.Path.ToLowerInvariant().EndsWith(".paml") || s.Path.ToLowerInvariant().EndsWith(".axaml"))
                 {
                     XamlFileInfo info;
                     try
@@ -150,7 +150,7 @@ namespace Avalonia.Build.Tasks
 
             BuildEngine.LogMessage($"GenerateAvaloniaResourcesTask -> Root: {Root}, {Resources?.Count()} resources, Output:{Output}", _reportImportance < MessageImportance.Low ? MessageImportance.High : _reportImportance);
 
-            foreach (var r in EmbeddedResources.Where(r => r.ItemSpec.EndsWith(".xaml") || r.ItemSpec.EndsWith(".paml")))
+            foreach (var r in EmbeddedResources.Where(r => r.ItemSpec.EndsWith(".xaml") || r.ItemSpec.EndsWith(".paml") || r.ItemSpec.EndsWith(".axaml")))
                 BuildEngine.LogWarning(BuildEngineErrorCode.LegacyResmScheme, r.ItemSpec,
                     "XAML file is packed using legacy EmbeddedResource/resm scheme, relative URIs won't work");
             var resources = BuildResourceSources();

src/Avalonia.Build.Tasks/XamlCompilerTaskExecutor.cs

@@ -25,7 +25,8 @@ namespace Avalonia.Build.Tasks
     public static partial class XamlCompilerTaskExecutor
     {
         static bool CheckXamlName(IResource r) => r.Name.ToLowerInvariant().EndsWith(".xaml")
-                                               || r.Name.ToLowerInvariant().EndsWith(".paml");
+                                               || r.Name.ToLowerInvariant().EndsWith(".paml")
+                                               || r.Name.ToLowerInvariant().EndsWith(".axaml");
         
         public class CompileResult
         {