Could not install the app on the device, read the error above for details.
Make sure you have an Android emulator running or a device connected and have
set up your Android development environment:
https://facebook.github.io/react-native/docs/android-setup.html
我已经按照好genymotion emulator 并且启动了一个模拟，此外，android studio ，virtual box 也安装好了，估计是有什么没有配置好？
你可以尝试以下方法，看行不行，我之前出过个问题，是按照下面方法改好的。
修改Genymotion->Settings->ADB tool connection settings 为Use custom Andrdoid SDK tools，并选择对应的Android SDK目录。