Issues creating a nuget package referening Xamarin Forms - visual-studio

Question

I'm creating a nuget package that is refercing a number of different packages for the platforms.
I don't sem to be able to reference Xam.Forms.Platform. from the various ItemGroups as well as packages I've added via nuget for specific platforms.
I'm using this as a reference : https://learn.microsoft.com/en-us/nuget/guides/create-packages-for-xamarin and my csproj is this
<Project Sdk="MSBuild.Sdk.Extras/2.0.54">
<PropertyGroup>
<!--Work around so the conditions work below-->
<TargetFrameworks></TargetFrameworks>
<TargetFrameworks Condition=" '$(OS)' ==
'Windows_NT'">netstandard2.0;Xamarin.iOS10;MonoAndroid90;uap10.0.16299</TargetFrameworks>
<TargetFrameworks Condition=" '$(OS)' !=
'Windows_NT'">netstandard2.0;Xamarin.iOS10;MonoAndroid90</TargetFrameworks>
<AssemblyName>Plugin.Mobile.Xamarin</AssemblyName>
<RootNamespace>Plugin.Mobile.Xamarin</RootNamespace>
<PackageId>Plugin.Mobile.Xamarin</PackageId>
<Product>Plugin.Mobile.Xamarin</Product>
<AssemblyVersion>1.0.0.0</AssemblyVersion>
<AssemblyFileVersion>1.0.0.0</AssemblyFileVersion>
<Version>1.0.0.0</Version>
<PackageVersion>1.0.0.0</PackageVersion>
<PackOnBuild>true</PackOnBuild>
<NeutralLanguage>en</NeutralLanguage>
<LangVersion>default</LangVersion>
<DefineConstants>$(DefineConstants);</DefineConstants>
<UseFullSemVerForNuGet>false</UseFullSemVerForNuGet>
<EnableDefaultCompileItems>false</EnableDefaultCompileItems>
<LangVersion>latest</LangVersion>
<DebugType>portable</DebugType>
<PropertyGroup Condition=" '$(Configuration)'=='Debug' ">
<DebugSymbols>true</DebugSymbols>
<GenerateDocumentationFile>false</GenerateDocumentationFile>
</PropertyGroup>
<PropertyGroup Condition=" '$(Configuration)'=='Release' ">
<GeneratePackageOnBuild>true</GeneratePackageOnBuild>
<GenerateDocumentationFile>true</GenerateDocumentationFile>
</PropertyGroup>
<ItemGroup>
<Compile Include="**\*.cs" />
</ItemGroup>
<ItemGroup>
<PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.2.10" />
<PackageReference Include="Newtonsoft.Json" Version="12.0.3" />
<PackageReference Include="Xamarin.Essentials" Version="1.5.3.2" />
<PackageReference Include="Xamarin.Forms" Version="4.7.0.1179" />
<PackageReference Include="Xamarin.Forms.Visual.Material" Version="4.7.0.1179" />
<PackageReference Include="SkiaSharp.Views.Forms" Version="2.80.1" />
</ItemGroup>
<ItemGroup>
<None Update="Langs.Designer.cs">
<DesignTime>True</DesignTime>
<AutoGen>True</AutoGen>
<DependentUpon>Langs.resx</DependentUpon>
</None>
</ItemGroup>
<ItemGroup>
<None Update="shared\Langs.Designer.cs">
<DesignTime>True</DesignTime>
<AutoGen>True</AutoGen>
<DependentUpon>Langs.resx</DependentUpon>
</None>
</ItemGroup>
<ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
<PackageReference Include="SkiaSharp.Views.Forms">
<Version>2.80.1</Version>
</PackageReference>
<PackageReference Include="Xamarin.Essentials" Version="1.5.3.2" />
</ItemGroup>
<ItemGroup Condition="'$(TargetFramework)' == 'uap10.0.16299'">
<PackageReference Include="Microsoft.NETCore.UniversalWindowsPlatform" Version="6.2.9" />
<Reference Include="Microsoft.CSharp" />
<PackageReference Include="SkiaSharp.Views.Forms">
<Version>2.80.1</Version>
</PackageReference>
<PackageReference Include="Xamarin.Forms" Version="4.7.0.1179" />
<PackageReference Include="Xamarin.Forms.Visual.Material" Version="4.7.0.1179" />
<SDKReference Include="WindowsMobile, Version=10.0.16299.0">
<Name>Windows Mobile Extensions for the UWP</Name>
</SDKReference>
<Compile Include="**\UWP*.cs" />
</ItemGroup>
<ItemGroup Condition="'$(TargetFramework)' == 'Xamarin.iOS10'">
<Reference Include="Xamarin.iOS">
<HintPath>..\..\..\..\..\..\..\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\ReferenceAssemblies\Microsoft\Framework\Xamarin.iOS\v1.0\Xamarin.iOS.dll</HintPath>
</Reference>
<Reference Include="Microsoft.CSharp" />
<PackageReference Include="EasyTipView">
<Version>1.0.1</Version>
</PackageReference>
<PackageReference Include="SkiaSharp.Views.Forms">
<Version>2.80.1</Version>
</PackageReference>
<PackageReference Include="Xamarin.Forms" Version="4.7.0.1179" />
<PackageReference Include="Xamarin.Forms.Visual.Material" Version="4.7.0.1179" />
<Compile Include="**\iOS*.cs" />
</ItemGroup>
<ItemGroup Condition=" $(TargetFramework.StartsWith('MonoAndroid')) ">
<Reference Include="Mono.Android">
<HintPath>..\..\..\..\..\..\..\Program Files (x86)\Microsoft Visual Studio\2019\Community\Common7\IDE\ReferenceAssemblies\Microsoft\Framework\MonoAndroid\v9.0\Mono.Android.dll</HintPath>
</Reference>
<PackageReference Include="SkiaSharp.Views.Forms">
<Version>2.80.1</Version>
</PackageReference>
<PackageReference Include="Xamarin.Android.Tooltips">
<Version>1.0.7</Version>
</PackageReference>
<PackageReference Include="System.Numerics.Vectors" Version="4.5.0" />
<Reference Include="System.Numerics" />
<PackageReference Include="Xamarin.Forms" Version="4.7.0.1179" />
<PackageReference Include="Xamarin.Forms.Visual.Material" Version="4.7.0.1179" />
<Compile Include="**\Droid*.cs" />
</ItemGroup>
</Project>
Any ideas on why I can't include or reference these packages?
The errors I'm seeing are the likes of

Answer 1

Any ideas on why I can't include or reference these packages?
The issue is caused by the project template Cross-Platform .NET Standard Library Plugin.
To be precise, this is due to the design of this special project template.
As the document said, you should use the corresponding platform namespace in xxx.<PLATFORM>.cs file of each platform project.
Suggestion
From your description, the namespaces you are using are all related to Android, so you should add these in the file <project_name>.andoroid.cswhich targets to MonoAndroid90.
And if you input them in the file called apple.cs,uwp.cs or others, the template is unable to identify them.
And you can see <project_name>.andoroid.cs file is connected with MonoAndroid90, so it can identify android namespaces and the same is true for other platform files.
In addition, if you still want your requirements, you should connect with the extension's author to reflect the issue.

Answer 2

try to change your TargetFrameworks become like this
<TargetFrameworks>netstandard2.0;Xamarin.iOS10;MonoAndroid90</TargetFrameworks>
<TargetFrameworks Condition=" '$(OS)' == 'Windows_NT' ">uap10.0.16299;$(TargetFrameworks)</TargetFrameworks>