在 android 中的应用程序启动期间，有没有办法知道设备的蓝牙连接状态？

Question

I have a use case where I want to know whether my Bluetooth is connected to any other device during my app startup time. Like I know we have a broadcast receiver to listen to connectivity status changes but specifically, I want to know at the app starting time whether it is connected to any other device or not. More specifically I have a wearOS watch and I'm running the app overwatch so I want to check whether it's connected to the phone or not

Answer 1

TL;DR: There is no direct way to find out the connected devices for non-system apps. But there is a hack to figure out the connected devices, with less guarantee.

System apps such as Android settings use BluetoothDevice.isConnected() API to get the current connection status of paired/bonded devices. This system API can't be used by non-system apps.

Here is how a non-system app can figure out connected device:

0. Make sure all required bluetooth permission are mentioned in manifest and granted.
1. Get list of paired/bonded devices by calling BluetoothAdapter.getBondedDevices()
2. Now we will try to establish socket connection to each device via RFCOMM socket .
3. If the API throws any error, then most probably the devices aren't connected, or can't connect.
4. Now if the socket connection is established then there is a chance the devices are connected. To verify if device is connected by calling isConnected() on the socket connection.

This way you can identify all the connected devices. Now this is a resource intensive task. I would recommend to do it once at the beginning. Post that until your app is active listen to ACTION_ACL_CONNECTED and ACTION_ACL_DISCONNECTED broadcasts.