从特征写入和读取

一旦连接到 Gatt 服务器，你就可以通过写入和读取服务器的特性来与它进行交互。要做到这一点，首先你必须了解此服务器上可用的服务以及每个服务中可用的特征：

 @Override
 public void onConnectionStateChange(BluetoothGatt gatt, int status,
        int newState) {
    if (newState == BluetoothProfile.STATE_CONNECTED) {
        Log.i(TAG, "Connected to GATT server.");
        gatt.discoverServices();

    }
. . .

 @Override
    public void onServicesDiscovered(BluetoothGatt gatt, int status) {
        if (status == BluetoothGatt.GATT_SUCCESS) {
             List<BluetoothGattService> services = gatt.getServices();
                for (BluetoothGattService service : services) {
                    List<BluetoothGattCharacteristic> characteristics = service.getCharacteristics();
                    for (BluetoothGattCharacteristic characteristic : characteristics) { 
                        ///Once you have a characteristic object, you can perform read/write
                        //operations with it         
                    }
                 }
              }
            }

基本的写操作如下：

characteristic.setValue(newValue);
characteristic.setWriteType(BluetoothGattCharacteristic.WRITE_TYPE_DEFAULT);
gatt.writeCharacteristic(characteristic);

写入过程完成后，将调用 BluetoothGattCallback 的 onCharacteristicWrite 方法：

    @Override
    public void onCharacteristicWrite(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
        super.onCharacteristicWrite(gatt, characteristic, status);
        Log.d(TAG, "Characteristic " + characteristic.getUuid() + " written);
    }

基本的写操作如下：

gatt.readCharacteristic(characteristic);

写入过程完成后，将调用 BluetoothGattCallback 的 onCharacteristicRead 方法：

@Override
public void onCharacteristicRead(BluetoothGatt gatt, BluetoothGattCharacteristic characteristic, int status) {
  super.onCharacteristicRead(gatt, characteristic, status);
  byte[] value = characteristic.getValue();
  }