构建我的 c# 项目时，我收到“在未引用的程序集中定义”错误，如何解决？

Question

I have already have references to System and System.Data.

1.The type 'System.ComponentModel.IListSource' is defined in an assembly that is not referenced. You must add a reference to assembly 'System, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

2.The type 'System.Data.Common.DbDataReader' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

3.The type 'System.Data.IDataRecord' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

4.The type 'System.Data.Common.DbConnection' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Data, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089'.

I have already have references to System and System.Data.

Answer 1

Im going to drop my solution. I restarted visual studio.

Answer 2

You need to add references to assemblies where there type are defines. To add reference to an assembly; right click on the Reference nodes under your project and select the assemblies node on the left tree and

1. add reference to System.dll , which will show up as System on the right side
2. add reference to System.Data.dll , which will show up as System.Data on the right side

Answer 3

In my case I was getting error as

You must add a reference to assembly netstandard, Version=2.0.0.0

It was resolved by following steps

1. In Visual studio - Solution explorer right click on the project and choose unload so that you are able to edit the .proj file.
2. Locate the last tag of tags in side the t tag.
3. After add an new tag as below:

 <ItemGroup> <Reference Include="netstandard" /> </ItemGroup>

4. Save the file.
5. Again right click on project and choose Reload project.