خطا هنگام اجرای برنامه react native run android

سلام موقعی که برنامه react native run android میزنم خطایه زیر رو میده
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Task :app:installDebug FAILED

FAILURE: Build failed with an exception.

• What went wrong:
  Execution failed for task ':app:installDebug'.

  com.android.builder.testing.api.DeviceException: No connected devices!

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full
  insights.

• Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/5.4.1/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 1m 14s
26 actionable tasks: 1 executed, 25 up-to-date
error 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
error Command failed: gradlew.bat app:installDebug. Run CLI with --verbose flag for more details.
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