Could not resolve com.android.support:appcompat-v7:26.1.0. Required by: project :app No cached version of com.android.support:appcompat-v7:26.1.0 available for offline mode. No cached version of com.android.support:appcompat-v7:26.1.0 available for offline mode. Could not resolve com.android.support.constraint:constraint-layout:1.1.0-beta3. Required by: project :app No cached version of com.android.support.constraint:constraint-layout:1.1.0-beta3 available for offline mode. No cached version of com.android.support.constraint:constraint-layout:1.1.0-beta3 available for offline mode. Could not resolve com.android.support:design:26.1.0. Required by: project :app No cached version of com.android.support:design:26.1.0 available for offline mode. No cached version of com.android.support:design:26.1.0 available for offline mode. Could not resolve com.android.support:cardview-v7:26.1.0. Required by: project :app No cached version of com.android.support:cardview-v7:26.1.0 available for offline mode. No cached version of com.android.support:cardview-v7:26.1.0 available for offline mode. Could not resolve com.google.android.gms:play-services-ads:11.4.2. Required by: project :app No cached version of com.google.android.gms:play-services-ads:11.4.2 available for offline mode. No cached version of com.google.android.gms:play-services-ads:11.4.2 available for offline mode. Could not resolve com.android.support:support-v4:26.1.0. Required by: project :app No cached version of com.android.support:support-v4:26.1.0 available for offline mode. No cached version of com.android.support:support-v4:26.1.0 available for offline mode.
这个问题折腾了我很久 ，就是依赖了一些三方的包，但是一直就是找不到。
解决方法最后终于找到了：
File->Settings->Build, Execution, Deployment->Gradle->Uncheck Offline work option.offline mode.
不要选择gradle 离线工作 模式 再试一下就好了，特意标记一下，也希望能帮助到其他小伙伴。
