复制DllImport用的Dll文件到项目输出目录

打开项目的csproj文件
添加如下代码

 <ItemGroup>
    <None Remove="lib\xxx.dll" />
    <Content Include="lib\xxx.dll">
      <Link>xxx.dll</Link>
      <CopyToOutputDirectory>Always</CopyToOutputDirectory>
    </Content>
  </ItemGroup>