如何以编程方式判断蓝牙设备是否已连接？

Add the Bluetooth permission to your AndroidManifest,

<uses-permission android:name="android.permission.BLUETOOTH" />

Then use intent filters to listen to the ACTION_ACL_CONNECTED, ACTION_ACL_DISCONNECT_REQUESTED, and ACTION_ACL_DISCONNECTED broadcasts:

public void onCreate() {
...
IntentFilter filter = new IntentFilter();
filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED);
filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED);
filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);
this.registerReceiver(mReceiver, filter);
}


//The BroadcastReceiver that listens for bluetooth broadcasts
private final BroadcastReceiver mReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();
BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);


if (BluetoothDevice.ACTION_FOUND.equals(action)) {
... //Device found
}
else if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {
... //Device is now connected
}
else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(action)) {
... //Done searching
}
else if (BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED.equals(action)) {
... //Device is about to disconnect
}
else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {
... //Device has disconnected
}
}
};

A few notes:

• There is no way to retrieve a list of connected devices at application startup. The Bluetooth API does not allow you to query, instead it allows you to listen to changes.
• A hoaky workaround to the above problem would be to retrieve the list of all known/paired devices... then trying to connect to each one (to determine if you're connected).
• Alternatively, you could have a background service watch the Bluetooth API and write the device states to disk for your application to use at a later date.

For some reason, BluetoothAdapter.ACTION_ACL_CONNECTED could not be resolved by Android Studio. Perhaps it was deprecated in Android 4.2.2?

Here is a modification of Skylarsutton's code (Big thanks to Skylarsutton for his answer.) . The registration code is the same; the receiver code differs slightly. I use this in a service which updates a Bluetooth-connected flag that other parts of the app reference.

    public void onCreate() {
//...
IntentFilter filter = new IntentFilter();
filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED);
filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECT_REQUESTED);
filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);
this.registerReceiver(BTReceiver, filter);
}


//The BroadcastReceiver that listens for bluetooth broadcasts
private final BroadcastReceiver BTReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
String action = intent.getAction();


if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(action)) {
//Do something if connected
Toast.makeText(getApplicationContext(), "BT Connected", Toast.LENGTH_SHORT).show();
}
else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(action)) {
//Do something if disconnected
Toast.makeText(getApplicationContext(), "BT Disconnected", Toast.LENGTH_SHORT).show();
}
//else if...
}
};

In my use case I only wanted to see if a Bluetooth headset is connected for a VoIP app. The following solution worked for me.

Kotlin:

fun isBluetoothHeadsetConnected(): Boolean {
val mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter()
return (mBluetoothAdapter != null && mBluetoothAdapter.isEnabled
&& mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == BluetoothHeadset.STATE_CONNECTED)
}

Java:

public static boolean isBluetoothHeadsetConnected() {
BluetoothAdapter mBluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
return mBluetoothAdapter != null && mBluetoothAdapter.isEnabled()
&& mBluetoothAdapter.getProfileConnectionState(BluetoothHeadset.HEADSET) == BluetoothHeadset.STATE_CONNECTED;
}

Of course you'll need the Bluetooth permission:

<uses-permission android:name="android.permission.BLUETOOTH" />

BluetoothAdapter.getDefaultAdapter().isEnabled -> returns true when Bluetooth is open.

val audioManager = this.getSystemService(Context.AUDIO_SERVICE) as AudioManager

audioManager.isBluetoothScoOn -> returns true when a device connected

This code is for the headset profiles, and probably it will work for other profiles too.

First you need to provide a profile listener (Kotlin code):

private val mProfileListener = object : BluetoothProfile.ServiceListener {
override fun onServiceConnected(profile: Int, proxy: BluetoothProfile) {
if (profile == BluetoothProfile.HEADSET)
mBluetoothHeadset = proxy as BluetoothHeadset
}


override fun onServiceDisconnected(profile: Int) {
if (profile == BluetoothProfile.HEADSET) {
mBluetoothHeadset = null
}
}
}

Then while checking Bluetooth:

mBluetoothAdapter.getProfileProxy(context, mProfileListener, BluetoothProfile.HEADSET)
if (!mBluetoothAdapter.isEnabled) {
return Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE)
}

It takes a bit of time until onSeviceConnected is called. After that you may get the list of the connected headset devices from:

mBluetoothHeadset!!.connectedDevices

There is an isConnected function in the BluetoothDevice system API in https://android.googlesource.com/platform/frameworks/base/+/master/core/java/android/bluetooth/BluetoothDevice.java.

If you want to know if a bounded (paired) device is currently connected or not, the following function works fine for me:

public static boolean isConnected(BluetoothDevice device) {
try {
Method m = device.getClass().getMethod("isConnected", (Class[]) null);
boolean connected = (boolean) m.invoke(device, (Object[]) null);
return connected;
} catch (Exception e) {
throw new IllegalStateException(e);
}
}

I was really looking for a way to fetch the connection status of a device, not listen to connection events. Here's what worked for me:

BluetoothManager bm = (BluetoothManager) context.getSystemService(Context.BLUETOOTH_SERVICE);
List<BluetoothDevice> devices = bm.getConnectedDevices(BluetoothProfile.GATT);
int status = -1;


for (BluetoothDevice device : devices) {
status = bm.getConnectionState(device, BLuetoothGatt.GATT);
// compare status to:
//   BluetoothProfile.STATE_CONNECTED
//   BluetoothProfile.STATE_CONNECTING
//   BluetoothProfile.STATE_DISCONNECTED
//   BluetoothProfile.STATE_DISCONNECTING
}