问题
My Android app uses BLE APIs, and one of these APIs, BluetoothGattCallback.onConnectionStateChange(), receives an undocumented error code 19. I'm using Nexus 9.
Did anybody ever see this error code before? Like I mentioned above, this is undocumented in the Android API reference, and I don't know what to do about it.
P.S.I searched issue tickets at Android issue tracker also, and found that developers encounter undocumented, BLE-related error codes often. Hmm, this is grim.
来源：https://stackoverflow.com/questions/27501770/bluetooth-le-undocumented-error-code-19