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react-native- run-android میزنم ارور زیر رو بهم میده
FAILURE: Build failed with an exception.

BUILD FAILED in 2m 1s
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/getting-started.html