webApi添加视图出现/Index.cshtml”处的视图必须派生自 WebViewPage 或 WebViewPage。

是因为webapi views文件夹下缺乏web.config文件，从mvc项目相同目录拷贝一个web.config文件放入 删除多余的namespaces 即可

web.config配置如下：

<?xml version="1.0"?>

<configuration>
  <configsections>
    <sectiongroup name="system.web.webpages.razor" type="system.web.webpages.razor.configuration.razorwebsectiongroup, system.web.webpages.razor, version=3.0.0.0, culture=neutral, publickeytoken=31bf3856ad364e35">
      <section name="host" type="system.web.webpages.razor.configuration.hostsection, system.web.webpages.razor, version=3.0.0.0, culture=neutral, publickeytoken=31bf3856ad364e35" requirepermission="false" />
      <section name="pages" type="system.web.webpages.razor.configuration.razorpagessection, system.web.webpages.razor, version=3.0.0.0, culture=neutral, publickeytoken=31bf3856ad364e35" requirepermission="false" />
    </sectiongroup>
  </configsections>

  <system.web.webpages.razor>
    <host factorytype="system.web.mvc.mvcwebrazorhostfactory, system.web.mvc, version=5.2.3.0, culture=neutral, publickeytoken=31bf3856ad364e35" />
    <pages pagebasetype="system.web.mvc.webviewpage">
      <namespaces>
        <add namespace="system.web.mvc" />
        <add namespace="system.web.mvc.ajax" />
        <add namespace="system.web.mvc.html" />
        <add namespace="system.web.optimization"/>
        <add namespace="system.web.routing" />
      </namespaces>
    </pages>
  </system.web.webpages.razor>

  <appsettings>
    <add key="webpages:enabled" value="false" />
  </appsettings>

  <system.webserver>
    <handlers>
      <remove name="blockviewhandler"/>
      <add name="blockviewhandler" path="*" verb="*" precondition="integratedmode" type="system.web.httpnotfoundhandler" />
    </handlers>
  </system.webserver>

  <system.web>
    <compilation>
      <assemblies>
        <add assembly="system.web.mvc, version=5.2.3.0, culture=neutral, publickeytoken=31bf3856ad364e35" />
      </assemblies>
    </compilation>
  </system.web>
</configuration>