**一运行react-native run-andorid就报这个错误**
```
02:49:39 E/ddms: 'E:\android\sdk\platform-tools\adb.exe,start-server' failed -- run manually if necessary
:app:installDebug FAILED

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:installDebug'.
> com.android.builder.testing.api.DeviceException: java.lang.RuntimeException: Timeout getting device list.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output.

BUILD FAILED

Total time: 43.302 secs
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
```