Android Programming - Getting Started with Bluetooth Low Energy - page 115

processed gets silently dropped. This can be a source of frustration because it simply
looks like a device is not responding.
The correct sequence of operations is to send a request and wait for the appopriate
callback. For example, you would send a read request to the remote device to read a
particular characteristic. After the device responds, the BleWrapper will issue a callback
to uiNewValueForCharacteristic with the characteristic information. By doing so,
you are implementing the Read chacteristic value GATT feature explained in “Reading
Characteristics and Descriptors” on page 70 .
This code requests a read of the accelerometer's configuration characteristic:
BluetoothGatt gatt ;
BluetoothGattCharacteristic c ;
gatt = mBleWrapper . getGatt ();
c = gatt . getService ( UUID_ACC_SERV ). getCharacteristic ( UUID_ACC_CONF );
mBleWrapper . requestCharacteristicValue ( c );
Once the the request is issued, the device will respond with the characteristic's data. In
this case, you're going to dump each byte of the characteristic's raw value to logcat :
@Override
public void uiNewValueForCharacteristic ( BluetoothGatt gatt ,
BluetoothDevice device ,
BluetoothGattService service ,
BluetoothGattCharacteristic ch ,
String strValue ,
int intValue ,
byte [] rawValue ,
String timestamp )
{
super . uiNewValueForCharacteristic ( gatt , device , service ,
ch , strValue , intValue ,
rawValue , timestamp );
Log . d ( LOGTAG , "uiNewValueForCharacteristic" );
for ( byte b: rawValue )
{
Log . d ( LOGTAG , "Val: " + b );
}
}
It's important to remember that each read or write must be requested. There are func‐
tions in Android's BLE library to get and set a value for characteristics. These operate
only on the locally stored values and not on the remote device. In most cases, any
interaction with the remote device will require the use of callbacks.
Before you read any of the sensor's data, you first need to enable them. To do this, you
have to write a value to their configuration characteristic (those are proprietary char‐
acteristics to enable sensors, not to be confused with CCCDs ). In most cases, you'd just