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The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'mscorlib, Version=2.0.5.0


This issue was not unlike others that I have come up against with my cross-device mobile development efforts.

- February 12, 2017

Rest of the Story:

Another day, another issue while building a Xamarin project. In this case, I was building a project from Xamarin and working through some logic. When building the Android project I was presented with the following build errors. I am getting use to different errors at the most unexpected times. This issue was not unlike others that I have come up against with my cross-device mobile development efforts. The good news, after much hunting and packing I found the solution. See below.

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Severity Code Description Project File Line Suppression State
Error CS0012 The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'mscorlib, Version=2.0.5.0, Culture=neutral,

PublicKeyToken=7cec85d7bea7798e'. GreatQuotes.Android C:\Xamarin\10a_xam300\Lab Materials\Part 01 Resources\Start\GreatQuotes.Android\App.cs 9 ActiveError CS0234 The type or namespace name 'TargetFrameworkAttributeAttribute' does not exist in the namespace 'System.Runtime.Versioning' (are you missing an assembly reference?) GreatQuotes.Android

C:\Users\dyardy\AppData\Local\Temp\MonoAndroid,Version=v7.1.AssemblyAttributes.cs 4 ActiveError CS0234 The type or namespace name 'TargetFrameworkAttribute' does not exist in the namespace 'System.Runtime.Versioning' (are you missing an assembly reference?) 
GreatQuotes.Android C:\Users\dyardy\AppData\Local\Temp\MonoAndroid,Version=v7.1.AssemblyAttributes.cs 4 ActiveError CS0518 Predefined type 'System.String' is not defined or imported GreatQuotes.Android C:\Users\dyardy\AppData\Local\Temp\MonoAndroid,Version=v7.1.AssemblyAttributes.cs 4 ActiveError CS0246 The type or namespace name 'FrameworkDisplayName' could not be found (are you missing a using directive or an assembly reference?) GreatQuotes.Android

C:\Users\dyardy\AppData\Local\Temp\MonoAndroid,Version=v7.1.AssemblyAttributes.cs 4 ActiveError CS0518 Predefined type 'System.String' is not defined or imported GreatQuotes.Android C:\Users\dyardy\AppData\Local\Temp\MonoAndroid,Version=v7.1.AssemblyAttributes.cs 4 ActiveError CS0518 Predefined type 'System.Object' 
is not defined or imported 
GreatQuotes.Android C:\Xamarin\10a_xam300\Lab Materials\Part 01 Resources\Start\GreatQuotes.Android\App.cs 9 Active
Error CS0518 Predefined type 'System.Void' is not defined or imported GreatQuotes.Android C:\Xamarin\10a_xam300\Lab Materials\Part 01 Resources\Start\GreatQuotes.Android\App.cs 9 ActiveError CS0012 The type 'Object' is defined in an assembly that is not referenced. 

You must add a reference to assembly 'mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'. GreatQuotes.Android C:\Xamarin\10a_xam300\Lab Materials\Part 01 Resources\Start\GreatQuotes.Android\App.cs 9 Active

Error CS0246 The type or namespace name 'Icon' could not be found (are you missing a using directive or an assembly reference?) GreatQuotes.Android C:\Xamarin\10a_xam300\Lab Materials\Part 01 Resources\Start\GreatQuotes.Android\App.cs 9 ActiveError CS0518 Predefined type 'System.Object' is not defined or imported GreatQuotes.Android 

C:\Xamarin\10a_xam300\Lab Materials\Part 01 Resources\Start\GreatQuotes.Android\App.cs 9 Active
Error CS0518 Predefined type 'System.String' is not defined or imported GreatQuotes.Android C:\Xamarin\10a_xam300\Lab Materials\Part 01 

Resources\Start\GreatQuotes.Android\App.cs 9 ActiveError CS0012 The type 'Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'mscorlib, Version=2.0.5.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e'.
GreatQuotes.Android C:\Xamarin\10a_xam300\Lab Materials\Part 01 Resources\Start\GreatQuotes.Android\App.cs 9 Active
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The solution (to make a very long story short) was to unload the project from Visual Studio. Open the csproj and add the following reference (in bold). I initially was comparing some of my working Android projects with this one that just would not build.

I noticed the reference to mscorlib. I tried to add a reference to this dll directly through ‘Add Reference’ but I got the following error "mscorlib.dll" component is already automatically referenced. The build system should add this reference for you. Since I could not add through the VS.NET interface, i chose to add via csproj file. After reloading the project and rebuilding the reference to mscorlib was visible in the list of references and finally my project built fine.

<ItemGroup> 
    <Reference Include="Mono.Android" />
    <Reference Include="mscorlib" />
    <Reference Include="System" /> 
    <Reference Include="System.Xml" /> 
    <Reference Include="System.Core" /> 
    <Reference Include="System.Xml.Linq" />
</ItemGroup>
XML

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