BLE with Android 5.0 : How to get a device to act as Central AND Server?

Question

I'm using two Android 5.0 devices to communicate through Bluetooth Low Energy and I wan't :

• Device 1 to act as Central and Server.

• Device 2 to act as Peripheral and Client.

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This is the behavior I'd like to achieve :

1) Device 2 starts advertising (peripheral role).

2) Device 1 starts scanning (central role), and gets the advertising device (BluetoothDevice object) through the ScanCallback's onScanResult method.

3) I now want the advertising device (Device 2) to be notified that it has been scanned and be able to get the BluetoothDevice associated with Device 1.

4) Device 1 has an instance of BluetoothGattServer. Device 2 would now call connectGatt(Context context, boolean autoConnect, BluetoothGattCallback callback) on Device 1 to get an instance of BluetoothGatt.

5) In the end, Device 1 is Server and Device 2 is Client.

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So far I've found that in step 2, once Device 1 holds the BluetoothDevice for Device 2, it can only connect as client like in step 4 using connectGatt.

I might be able to use the BluetoothGattServer defined in Device 1, and call : gattServer.connect(BluetoothDevice device, boolean autoConnect) with device being Device 2.

But how will Device 2 be notified it's been connected to ?

And how will I get an instance of BluetoothGatt in Device 2 if I can't call connectGatt(Context, boolean, BluetoothGattCallback) on a BluetoothDevice?

Thank you in advance for your help !

Some documentation :

BluetoothGattServer

BluetoothDevice

Answer 1

1) Device 2 starts advertising (peripheral role).

Peripheral role will advertise, make sure to add CONNECTABLE

     AdvertiseSettings.Builder settingBuilder = new AdvertiseSettings.Builder();
     settingBuilder.setConnectable(true);

And start advertisement accordingly.

2) Device 1 starts scanning (central role), and gets the advertising device (BluetoothDevice object) through the ScanCallback's onScanResult method.

Perfect, now call connectGatt on this device(peripheral), make sure you stops the advertisement after you gets required device, otherwise you will end up sending multiple connect commands.

3) I now want the advertising device (Device 2) to be notified that it has been scanned and be able to get the BluetoothDevice associated with Device 1.

When you calls connectGatt from Central/client role, your peripheral will get a notification in its BluetoothGattServerCallback'onConnectionStateChange.

there you will know that connection has been made. though you have to register gatt Service with characteristics at peripheral side.

4) Device 1 has an instance of BluetoothGattServer. Device 2 would now call connectGatt(Context context, boolean autoConnect, BluetoothGattCallback callback) on Device 1 to get an instance of BluetoothGatt.

Wrong, Device 1 will initiate connection as I have stated in point 3. both device's onConnectionStateChange will be called to know that connection has been made.

5) In the end, Device 1 is Server and Device 2 is Client.

Wrong, Device 2 is peripheral(Server), Device 1 is Monitor(Client)