Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.suppo

Unable to resolve dependency for ':app@debug/compileClasspath': Could not resolve com.android.support.constraint:constraint-layout:1.1.1. Open File Show Details

这个错误主要是由于你现在依赖jar不能下载。打开Setting界面，搜索gradle，把offlinework取消选中，这样就能下载 了。

就不会报错了。