1. Device is not open developer options that allow USB debugging.
The reason for this non-existent, because the debugger must know who you want to allow USB debugging.
No corresponding driving device 2. The computer equipment can only as an ordinary USB, the device will not be recognized as Android.
Andrews pea pod on the computer, in the pea pod identification device installed device driver process, solve the problems identified.
3. Device Adb occupied by other applications, resulting in not identify Android Studio.
As mentioned in point 2, the device driver is installed, uninstall pea pods on computers and mobile phones, or pea pods will take Adb, resulting in Android Studio can not identify.