Service v/w Gatt connection in Android BLE API

Question

I am noticing in the adb logs that the services are discovered first and then the (gatt) connection is made with the device . Is it true? Isn't the gatt connection is made first and then the services are discovered from the slave device.

Answer 1

Explanation:

First you can get device connection state in onConnectionStateChange, Then if your device is connected state, you can Discover your device using gatt.discoverServices(). Then you can get service discovered response in onServicesDiscovered as state BluetoothGatt.GATT_SUCCESS. Now You can write on your device.

Code example:

  private BluetoothGattCallback gattCallback = new BluetoothGattCallback() {
    @Override
    public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
        super.onConnectionStateChange(gatt, status, newState);

        if (newState == BluetoothProfile.STATE_CONNECTED) {
                 // Device Connected, Now Discover your service
              gatt.discoverServices(); // You need to Discovered your gatt Service first
        } else if (newState == BluetoothProfile.STATE_DISCONNECTED) {

        }

    }

    @Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) {
        super.onServicesDiscovered(gatt, status);
        if (status == BluetoothGatt.GATT_SUCCESS) {
            // You can get discovered gatt service here. Now you can WRITE on your gatt service
        } 
    }

    @Override
    public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        super.onCharacteristicWrite(gatt, characteristic, status);
        if (status == BluetoothGatt.GATT_SUCCESS) {
          //You can get WRITE characteristic response here
        }
    }

    @Override

    public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        super.onCharacteristicRead(gatt, characteristic, status);
        if (status == BluetoothGatt.GATT_SUCCESS) {
          //You can get READ characteristic response here
        }
    }
};

I hope it's helps you.