android studio " Could not resolve com.android.support:appcompat-v7:26.1.0"

 在Android  studio 3.0 的新工程依赖 “ com.android.support:design:26.1.0” 时，sync错误，报以下问题：

   Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support:appcompat-v7:26.1.0

  No cached version of com.android.support:design:26.1.0 available for offline mode.

  因为缓存里面没有这个26.1.0的版本，去settings->Build,Execution,Deployment->Gradle，取消“offline work”的勾选，让studio去下载即可。