Prism: I create a Xamarin.Forms solution but Xamarin.Android cannot build

[vulcanlee]

My environment as following
Windows 10 : 1709
Visual Studio 2017 : 15.7.1
Prism Template Pack : 2.0.9

My problem is :

1. I create a Xamarin.Forms solution by Prism Template Pack

2. build the Xamarin.Android project, then I got following error message:

Error       Your project is not referencing the "MonoAndroid,Version=v8.1" framework. Add a reference to "MonoAndroid,Version=v8.1" in the "frameworks" section of your project.json, and then re-run NuGet restore.    BlankApp1.Android

But when I have changed the target Android version of Application of Xamarin.Android property to Android 7.1

And I can build this Xamarin.Adnroid project without any error and can run on emulator.

You can reference the test Visual Studio Project : https://github.com/vulcanlee/CannotBuildAndroid

[vulcanlee]

Following is the .csproj

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="4.0" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProductVersion>8.0.30703</ProductVersion>
    <SchemaVersion>2.0</SchemaVersion>
    <ProjectGuid>{BE0624F1-7930-439B-A633-DE63C4A4FC8B}</ProjectGuid>
    <ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>
    <OutputType>Library</OutputType>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>BlankApp1.Droid</RootNamespace>
    <AssemblyName>BlankApp1.Android</AssemblyName>
    <FileAlignment>512</FileAlignment>
    <TargetFrameworkVersion>v7.1</TargetFrameworkVersion>
    <AndroidApplication>True</AndroidApplication>
    <AndroidResgenFile>Resources\Resource.designer.cs</AndroidResgenFile>
    <GenerateSerializationAssemblies>Off</GenerateSerializationAssemblies>
    <AndroidResgenClass>Resource</AndroidResgenClass>
    <AndroidManifest>Properties\AndroidManifest.xml</AndroidManifest>
    <MonoAndroidResourcePrefix>Resources</MonoAndroidResourcePrefix>
    <MonoAndroidAssetsPrefix>Assets</MonoAndroidAssetsPrefix>
    <AndroidUseLatestPlatformSdk>true</AndroidUseLatestPlatformSdk>
    <AndroidStoreUncompressedFileExtensions />
    <MandroidI18n />
    <JavaMaximumHeapSize />
    <JavaOptions />
    <NuGetPackageImportStamp></NuGetPackageImportStamp>
  </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>
  </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="Mono.Android" />
    <Reference Include="System" />
    <Reference Include="System.Core" />
    <Reference Include="System.Xml.Linq" />
    <Reference Include="System.Xml" />
  </ItemGroup>
  <ItemGroup>
    <PackageReference Include="Xamarin.Forms" Version="2.5.0.122203" />
    <PackageReference Include="Xamarin.Android.Support.Design" Version="25.4.0.2" />
    <PackageReference Include="Xamarin.Android.Support.v7.AppCompat" Version="25.4.0.2" />
    <PackageReference Include="Xamarin.Android.Support.v4" Version="25.4.0.2" />
    <PackageReference Include="Xamarin.Android.Support.v7.CardView" Version="25.4.0.2" />
    <PackageReference Include="Xamarin.Android.Support.v7.MediaRouter" Version="25.4.0.2" />
    <PackageReference Include="Prism.Unity.Forms" Version="7.0.0.396" />
  </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="Assets\AboutAssets.txt" />
  </ItemGroup>
  <ItemGroup>
    <AndroidResource Include="Resources\mipmap-hdpi\ic_launcher.png" />
    <AndroidResource Include="Resources\mipmap-mdpi\ic_launcher.png" />
    <AndroidResource Include="Resources\mipmap-xhdpi\ic_launcher.png" />
    <AndroidResource Include="Resources\mipmap-xxhdpi\ic_launcher.png" />
    <AndroidResource Include="Resources\mipmap-xxxhdpi\ic_launcher.png" />
  </ItemGroup>
  <ItemGroup>
    <None Include="Properties\AndroidManifest.xml" />
  </ItemGroup>
  <ItemGroup>
    <AndroidResource Include="Resources\layout\Tabbar.axml" />
    <AndroidResource Include="Resources\layout\Toolbar.axml" />
    <AndroidResource Include="Resources\values\styles.xml">
      <SubType>Designer</SubType>
    </AndroidResource>
  </ItemGroup>
  <ItemGroup>
    <ProjectReference Include="..\BlankApp1\BlankApp1.csproj">
      <Project>{A682884C-CB44-4A89-B752-27BB634E0ABE}</Project>
      <Name>BlankApp1</Name>
    </ProjectReference>
  </ItemGroup>
  <Import Project="$(MSBuildExtensionsPath)\Xamarin\Android\Xamarin.Android.CSharp.targets" />
</Project>

[jbachelor]

I've seen this error numerous times on different solutions and different machines, both mac and pc. I've been most successful getting around this error by checking the Android sdk manager. I cannot explain why, but things seem to start working only when I've got Android 7.1, 8.0, and 8.1 all installed.

If it still won't compile after that, I recommend deleting all bin & obj directories in your solution's projects. Then restore nuget packages and try to build one more time.

I know this is not a satisfying answer, but at least it might help get you going. Perhaps someone else will be able to shed a bit more insight onto what's going on.

[dansiegel]

@vulcanlee the error would seem to be related to the issue that @jbachelor mentioned. Make sure that you have Android 8.1 SDK installed.

[vulcanlee]

@dansiegel

Yes, I have Android 8.1 SDK installed

[vulcanlee]

I have removed Android 8.1 SDK and the problem is disappeared.

Thanks for your help.

[nqbjnh]

I have the same problem.
Reason: file obj/project.assets.json target "MonoAndroid,Version=v7.1" when my project target android version 8.1
I resolved it by:

1. Right click Android project => Properties => Application => Compile
   using Android version => Android 7.1
2. Clean and Build project => build success, and restart IDE.
3. Right click Android project => Properties => Application => Compile
   using Android version => Android 8.1
4. Clean and Build project => build success

File obj/project.assets.json updated to "MonoAndroid,Version=v8.1"

[mopreni]

@nqbjnh Thank you!!!

[phamthanhtong]

@nqbjnh Could you explain me how to fix in Visual Studio for Mac?

[nqbjnh]

@nqbjnh Could you explain me how to fix in Visual Studio for Mac?
I don't use VS for Mac. I am not sure the same VS for Windows. You can check MonoAndroid version in project.assets.json file and project

[lock[bot]]

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