android studio 提示Error running app: No target device found.怎么办？？？

Question

12:14 Gradle build finished with 7 error(s) in 5s 553ms

12:15 Executing tasks: [:app:assembleDebug]

12:15 Gradle build finished with 7 error(s) in 5s 347ms

12:33 Error running app: No target device found.

12:34 Error running app: No target device found.