can not run-android

[WangJintong]

helen@helen-4441s:~/desktop/rn-world/react-native-demo-news$ react-native run-android
Starting JS server...
Building and installing the app on the device (cd android && ./gradlew installDebug...
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

[codingforme]

it tell you need connect a device or run an Android emulator.

[WangJintong]

thank you ,, it's ok after using emulator.