Unable to add directories and subdirectories inside Assets in a Xamarin Android Project.

IDE: Visual Studio Community For Mac Version:7.3.2 (build 12)

OS: MacOS High Sierra version: 10.13.2

Error: /Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(2,2): Error MSB3025: The source file "Assets/Dir/" is actually a directory. The "Copy" task does not support copying directories. (MSB3025) (assetsCheck)

/Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Android.Common.targets(2,2): Error MSB3025: The source file "Assets/Dir/SubDir/" is actually a directory. The "Copy" task does not support copying directories. (MSB3025) (assetsCheck)

Note Was able to build successfully using Visual Studio Community in a Windows 10 system.

.csproj file

<?xml version="1.0" encoding="utf-8"?>
<Project DefaultTargets="Build" ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="..\packages\Xamarin.Build.Download.0.4.3\build\Xamarin.Build.Download.props" Condition="Exists('..\packages\Xamarin.Build.Download.0.4.3\build\Xamarin.Build.Download.props')" />
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProjectGuid>{A6BF443D-8B89-4044-B951-E346FA8E68D3}</ProjectGuid>
    <ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
    <OutputType>Library</OutputType>
    <RootNamespace>ScormReader.Droid</RootNamespace>
    <AssemblyName>ScormReader.Droid</AssemblyName>
    <TargetFrameworkVersion>v8.0</TargetFrameworkVersion>
    <AndroidApplication>True</AndroidApplication>
    <AndroidResgenFile>Resources\Resource.designer.cs</AndroidResgenFile>
    <AndroidResgenClass>Resource</AndroidResgenClass>
    <AndroidManifest>Properties\AndroidManifest.xml</AndroidManifest>
    <MonoAndroidResourcePrefix>Resources</MonoAndroidResourcePrefix>
    <MonoAndroidAssetsPrefix>Assets</MonoAndroidAssetsPrefix>
    <AndroidUseLatestPlatformSdk>true</AndroidUseLatestPlatformSdk>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
    <DebugSymbols>true</DebugSymbols>
    <DebugType>full</DebugType>
    <Optimize>false</Optimize>
    <OutputPath>bin\Debug</OutputPath>
    <DefineConstants>DEBUG;</DefineConstants>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
    <AndroidLinkMode>None</AndroidLinkMode>
    <AndroidSupportedAbis>arm64-v8a;armeabi;armeabi-v7a;x86</AndroidSupportedAbis>
  </PropertyGroup>
  <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
    <DebugSymbols>true</DebugSymbols>
    <DebugType>pdbonly</DebugType>
    <Optimize>true</Optimize>
    <OutputPath>bin\Release</OutputPath>
    <ErrorReport>prompt</ErrorReport>
    <WarningLevel>4</WarningLevel>
    <AndroidManagedSymbols>true</AndroidManagedSymbols>
    <AndroidUseSharedRuntime>false</AndroidUseSharedRuntime>
  </PropertyGroup>
  <ItemGroup>
    <Reference Include="System" />
    <Reference Include="System.Xml" />
    <Reference Include="System.Core" />
    <Reference Include="Mono.Android" />
    <Reference Include="Xamarin.Android.Support.Annotations">
      <HintPath>..\packages\Xamarin.Android.Support.Annotations.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Annotations.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.Compat">
      <HintPath>..\packages\Xamarin.Android.Support.Compat.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Compat.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.Core.UI">
      <HintPath>..\packages\Xamarin.Android.Support.Core.UI.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Core.UI.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.Core.Utils">
      <HintPath>..\packages\Xamarin.Android.Support.Core.Utils.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Core.Utils.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.Media.Compat">
      <HintPath>..\packages\Xamarin.Android.Support.Media.Compat.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Media.Compat.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.Fragment">
      <HintPath>..\packages\Xamarin.Android.Support.Fragment.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Fragment.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.Vector.Drawable">
      <HintPath>..\packages\Xamarin.Android.Support.Vector.Drawable.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Vector.Drawable.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.Animated.Vector.Drawable">
      <HintPath>..\packages\Xamarin.Android.Support.Animated.Vector.Drawable.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.Animated.Vector.Drawable.dll</HintPath>
    </Reference>
    <Reference Include="Xamarin.Android.Support.v7.AppCompat">
      <HintPath>..\packages\Xamarin.Android.Support.v7.AppCompat.25.3.1\lib\MonoAndroid70\Xamarin.Android.Support.v7.AppCompat.dll</HintPath>
    </Reference>
  </ItemGroup>
  <ItemGroup>
    <Compile Include="MainActivity.cs" />
    <Compile Include="Resources\Resource.designer.cs" />
    <Compile Include="Properties\AssemblyInfo.cs" />
  </ItemGroup>
  <ItemGroup>
    <None Include="Resources\AboutResources.txt" />
    <None Include="Properties\AndroidManifest.xml" />
    <None Include="Assets\AboutAssets.txt" />
    <None Include="packages.config" />
  </ItemGroup>
  <ItemGroup>
    <AndroidResource Include="Resources\layout\Main.axml" />
    <AndroidResource Include="Resources\values\Strings.xml" />
    <AndroidResource Include="Resources\mipmap-hdpi\Icon.png" />
    <AndroidResource Include="Resources\mipmap-mdpi\Icon.png" />
    <AndroidResource Include="Resources\mipmap-xhdpi\Icon.png" />
    <AndroidResource Include="Resources\mipmap-xxhdpi\Icon.png" />
    <AndroidResource Include="Resources\mipmap-xxxhdpi\Icon.png" />
  </ItemGroup>
  <ItemGroup>
    <Folder Include="Resources\drawable\" />
  </ItemGroup>
  <ItemGroup>
  </ItemGroup>
  <ItemGroup>

  </ItemGroup>
  <ItemGroup>
    <AndroidAsset Include="Assets\Parent\" />
    <AndroidAsset Include="Assets\Parent\Child\" />
  </ItemGroup>
  <Import Project="$(MSBuildExtensionsPath)\Xamarin\Android\Xamarin.Android.CSharp.targets" />
  <Import Project="..\packages\Xamarin.Build.Download.0.4.3\build\Xamarin.Build.Download.targets" Condition="Exists('..\packages\Xamarin.Build.Download.0.4.3\build\Xamarin.Build.Download.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Annotations.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Annotations.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Annotations.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Annotations.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Compat.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Compat.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Compat.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Compat.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Core.UI.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Core.UI.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Core.UI.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Core.UI.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Core.Utils.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Core.Utils.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Core.Utils.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Core.Utils.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Media.Compat.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Media.Compat.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Media.Compat.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Media.Compat.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Fragment.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Fragment.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Fragment.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Fragment.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Vector.Drawable.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Vector.Drawable.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Vector.Drawable.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Vector.Drawable.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.Animated.Vector.Drawable.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Animated.Vector.Drawable.targets" Condition="Exists('..\packages\Xamarin.Android.Support.Animated.Vector.Drawable.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.Animated.Vector.Drawable.targets')" />
  <Import Project="..\packages\Xamarin.Android.Support.v7.AppCompat.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.v7.AppCompat.targets" Condition="Exists('..\packages\Xamarin.Android.Support.v7.AppCompat.25.3.1\build\MonoAndroid70\Xamarin.Android.Support.v7.AppCompat.targets')" />
</Project>

The "Copy" task does not support copying directories.

I reproduced your problem on my MacOS, and found the fix. When you added the sub-directory, the csproj file had an item added that causes this error. Edit the csproj file and remove the line that references the sub-directory will solve this probelm.

Solution :

My .csproj file :

<ItemGroup>   
    <AndroidAsset Include="Assets\New Folder\hi.txt">
        <Generator>RazorTemplatePreprocessor</Generator>
        <LastGenOutput>hi.cs</LastGenOutput>
    </AndroidAsset>    
    <AndroidAsset Include="Assets\New Folder1\" /> 
</ItemGroup>

Remove the first AndroidAsset that refers to the sub-directory :