Bluetooth
and BLE
BLE standards for Bluetooth Low Energy, which is standardized as Bluetooth 4.0. It doesn't intended to replace or enhance classic Bluetooth (2.0/3.0). It is designed with a new protocol stack for the specific services/applications which required much lower power consumption for getting much longer lifetime.
BLE defines following roles in GAP from the perspective of BLE .
- Peripheral device
The peripheral device broadcast
- Central device
I think you can find a lot of more information in the other public websites. Therefore the detail about BLE is not introduced here. The major focus here is to let you know BLE programming for Android.
BLE
Working Flow
Generally the BLE programming on a smartphone or table works as a central device. It scans the peripheral devices and then connect to it. The connection then will be used to access the peripheral device's attributes/characteristics or wait for the notification from peripheral device. You can refer to the profile document to know more detail about how to access the attributes/characteristics.
Below I divided a complete BLE session into following pieces from the role of a central device.
1.
Scan BLE device
2.
Connect to a device
3.
Read/write BLE attributes (characteristics)
4.
Receive GATT notification (optional, based on the need of profile)
BLE
Permission Declaration
Before starting the BLE programming, you have to declare enough permissions for BLE operations on an Android device. Below are the permissions you should add in your App.
Declare the Bluetooth permission(s) in your application manifest file.
<uses-permission
android:name="android.permission.BLUETOOTH"/>
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN"/>
If you want to declare that your app is available to BLE-capable devices
only, include the following in your app's manifest:
<uses-feature
android:name="android.hardware.bluetooth_le" android:required="true"/>
Android
BLE API
Android starts to support BLE since 4.3 (API
level 18). It introduced the Bluetooth LE related functions as below:
BLE scanning function was added in the
existing class “BluetoothAdapter” which works originally for the traditional
Bluetooth (2.0/3.0). More classes were also added to support BLE features
Since Lollipop (API level 21), a new
package “android.bluetooth.le” was introduced to address the BLE device scanning
and advertising. The class “BluetoothLeScanner” is used to replace the Bluetooth
LE scanning function
Device
scanning:
(BluetoothManager)
getSystemService(Context.BLUETOOTH_SERVICE);
API
level 18 ~ 20
BluetoothAdapter
= BluetoothManager.getAdapter()
BluetoothAdapter.startLeScan()
API
level 21 or later
BluetoothAdapter
= BluetoothManager.getAdapter()
BluetoothLeScanner
= BluetoothAdapter.getBluetoothLeScanner()
BluetoothLeScanner.startScan()
Device
Connecting
To setup a connection, you need to create a
service to receive the response of a service request.
Use bindService to bind this service with
your activity. After it, the connectivity is managed by the event (intent) for
connection, profile attributes, characteristic
That’s why we need to do 2 things before
really starting the connecting.
-
Bind Service
-
Register Receivers to register
all intents in the activities from the BLE service you bind.
ACTION_GATT_CONNECTED connected
to a GATT server.
ACTION_GATT_DISCONNECTED disconnected from a GATT
server.
ACTION_GATT_SERVICES_DISCOVERED discovered GATT services.
ACTION_DATA_AVAILABLE received
data from the device. This can be a result of read or notification operations.
BluetoothDevice
= BluetoothAdapter.getRemoteDevice() // by giving device address
BluetoothGatt
= BluetoothDevice.connectGatt()
Speedup the reconnection
BluetoothGatt.connect()
Read/write
Attributes
-
After connecting to the remote
GATT server, you can request to get the service
BluetoothGattService = BluetoothGatt.getServices()
-
When you get the service, you
can use it to get its characteristic to read or write according to the
definition in the profile.
BluetoothGattCharacteristic
= BluetoothGattService.getCharacteristic()
Here I use the diagram below to illustrate the relationship of the classes.
Receive
GATT notification (optional)
