一、前言
在上一篇文章Android 蓝牙BLE开发从官方源码demo开始（一）我们已经看了官方的demo，知道了怎么开始配置Android蓝牙4.0，并且也成功地进行扫描并获取回调的蓝牙设备参数，然后对参数进行处理展示，其中第一个参数device，表示一个远程蓝牙设备，里面有它独有的蓝牙地址Address和Name；我们要拿到这个设备Address进行蓝牙连接和读写操作。
谷歌给我们提供了官方源码demo：
https://github.com/googlesamples/android-BluetoothLeGatt
接下来我们继续来学习谷歌官方给我们提供的蓝牙BLE源码
二、创建BluetoothLeService服务类并初始化蓝牙连接
在官方demo中，蓝牙ble的连接和读写操作都是在DeviceControlActivity中实现，可以下载demo源码，编译运行一遍！
来到此Activity，我们先看onCreate()方法可知，程序先执行bindService开启了一个服务
Intent gattServiceIntent = new Intent(this, BluetoothLeService.class);
bindService(gattServiceIntent, mServiceConnection, BIND_AUTO_CREATE);并在服务回调已经成功连接时，获取了BlueToohtLeService的实例，接着就执行蓝牙连接操作：
// Code to manage Service lifecycle.
private final ServiceConnection mServiceConnection = new ServiceConnection() {
@Override
public void onServiceConnected(ComponentName componentName, IBinder service) {
mBluetoothLeService = ((BluetoothLeService.LocalBinder) service).getService();
if (!mBluetoothLeService.initialize()) {
Log.e(TAG, "Unable to initialize Bluetooth");
finish();
}
// Automatically connects to the device upon successful start-up initialization.
mBluetoothLeService.connect(mDeviceAddress);
}
@Override
public void onServiceDisconnected(ComponentName componentName) {
mBluetoothLeService = null;
}
};这个BlueToohtLeService类既然是服务类，那它父类肯定是继承于Service；接着实现了Service的先进入onBind()方法；
1.onBind()是使用bindService开启的服务才会有回调的一个方法。
这里官方demo在onBind()方法给我们的Activity返回了BluetoothLeService实例，方便Activity后续的连接和读写操作；
private final IBinder mBinder = new LocalBinder();
public class LocalBinder extends Binder {
BluetoothLeService getService() {
return BluetoothLeService.this;
}
}
@Override
public IBinder onBind(Intent intent) {
return mBinder;
}2.当服务调用unbindService时，服务的生命周期将会进入onUnbind()方法；接着执行了关闭蓝牙的方法；
@Override
public boolean onUnbind(Intent intent) {
// After using a given device, you should make sure that BluetoothGatt.close() is called
// such that resources are cleaned up properly. In this particular example, close() is
// invoked when the UI is disconnected from the Service.
close();
return super.onUnbind(intent);
}3.initialize() 初始化蓝牙适配器；接着在这demo里这个方法是在服务建立后在Activity通过拿到BlueToohtLeService实例调用的。
/**
* Initializes a reference to the local Bluetooth adapter.
*
* @return Return true if the initialization is successful.
*/
public boolean initialize() {
// For API level 18 and above, get a reference to BluetoothAdapter through
// BluetoothManager.
if (mBluetoothManager == null) {
mBluetoothManager = (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
if (mBluetoothManager == null) {
Log.e(TAG, "Unable to initialize BluetoothManager.");
return false;
}
}
mBluetoothAdapter = mBluetoothManager.getAdapter();
if (mBluetoothAdapter == null) {
Log.e(TAG, "Unable to obtain a BluetoothAdapter.");
return false;
}
return true;
}4.connect()方法 传入蓝牙地址进行连接蓝牙操作；先判断蓝牙适配器是否为空，然后判断是否刚断开需要重连的设备，否则就通过蓝牙适配器获取BluetoothGatt实例去连接蓝牙操作，后续还会使用到BluetoothGatt去读写操作和断开、关闭操作；
public boolean connect(final String address) {
if (mBluetoothAdapter == null || address == null) {
Log.w(TAG, "BluetoothAdapter not initialized or unspecified address.");
return false;
}
// Previously connected device. Try to reconnect.
// 以前连接的设备。 尝试重新连接。
if (mBluetoothDeviceAddress != null && address.equals(mBluetoothDeviceAddress)
&& mBluetoothGatt != null) {
Log.d(TAG, "Trying to use an existing mBluetoothGatt for connection.");
if (mBluetoothGatt.connect()) {
mConnectionState = STATE_CONNECTING;
return true;
} else {
return false;
}
}
final BluetoothDevice device = mBluetoothAdapter.getRemoteDevice(address);
if (device == null) {
Log.w(TAG, "Device not found. Unable to connect.");
return false;
}
// We want to directly connect to the device, so we are setting the autoConnect 我们想直接连接到设备，因此我们设置autoConnect
// parameter to false.
mBluetoothGatt = device.connectGatt(this, false, mGattCallback);
Log.d(TAG, "Trying to create a new connection.");
mBluetoothDeviceAddress = address;
mConnectionState = STATE_CONNECTING;
return true;
}5.BluetoothGattCallback 回调；这个回调可以说很重要，核心部分，主要对BluetoothGatt的蓝牙连接、断开、读、写、特征值变化等的回调监听，然后我们可以将这些回调信息通过广播机制传播回给广播监听器。
private final BluetoothGattCallback mGattCallback = new BluetoothGattCallback() {
@Override
public void onConnectionStateChange(BluetoothGatt gatt, int status, int newState) {
}
@Override
public void onServicesDiscovered(BluetoothGatt gatt, int status) {
}
@Override
public void onCharacteristicRead(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic,
int status) {
}
@Override
public void onCharacteristicChanged(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic) {
}
};
三、广播监听器
在这个官方demo中，就是使用了广播来作为activity和service之间的数据传递；继续回到源码：activity开启前面所说的服务之后，就注册了这个mGattUpdateReceiver广播；
registerReceiver(mGattUpdateReceiver, makeGattUpdateIntentFilter());
if (mBluetoothLeService != null) {
final boolean result = mBluetoothLeService.connect(mDeviceAddress);
Log.d(TAG, "Connect request result=" + result) ;
}
private static IntentFilter makeGattUpdateIntentFilter() {
final IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction(BluetoothLeService.ACTION_GATT_CONNECTED);
intentFilter.addAction(BluetoothLeService.ACTION_GATT_DISCONNECTED);
intentFilter.addAction(BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED);
intentFilter.addAction(BluetoothLeService.ACTION_DATA_AVAILABLE);
return intentFilter;
}关于这个广播的回调监听如下：有注释就不多解释了，它的作用就是接收从service发送回来的信息；上文有说到BluetoothGattCallback，就是从这里发送广播的。
// Handles various events fired by the Service. 处理服务部门发起的各种事件
// ACTION_GATT_CONNECTED: connected to a GATT server. 连接到GATT服务器。
// ACTION_GATT_DISCONNECTED: disconnected from a GATT server. 与GATT服务器断开连接。
// ACTION_GATT_SERVICES_DISCOVERED: discovered GATT services.发现GATT服务
// ACTION_DATA_AVAILABLE: received data from the device. This can be a result of read
// or notification operations. 从设备接收数据。 这可能是阅读的结果
// //或通知操作。
private final BroadcastReceiver mGattUpdateReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
final String action = intent.getAction();
if (BluetoothLeService.ACTION_GATT_CONNECTED.equals(action)) {
mConnected = true;
updateConnectionState(R.string.connected);
invalidateOptionsMenu();
} else if (BluetoothLeService.ACTION_GATT_DISCONNECTED.equals(action)) {
mConnected = false;
updateConnectionState(R.string.disconnected);
invalidateOptionsMenu();
clearUI();
} else if (BluetoothLeService.ACTION_GATT_SERVICES_DISCOVERED.equals(action)) {
// Show all the supported services and characteristics on the user interface.
displayGattServices(mBluetoothLeService.getSupportedGattServices());
} else if (BluetoothLeService.ACTION_DATA_AVAILABLE.equals(action)) {
displayData(intent.getStringExtra(BluetoothLeService.EXTRA_DATA));
}
}
};这里留意一下：当连接成功后，首先service那边会发现服务特征值，通过广播传输回来，然后执行下面的方法：
displayGattServices(mBluetoothLeService.getSupportedGattServices());四、其他方法
1. setCharacteristicNotification()；调用此方法开启特征值的通知；
mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);2.开启读，我们可以用如下方法，但是此方法有个缺点：要不断轮询 才能达到不断监听；
mBluetoothGatt.readCharacteristic(characteristic);如果成功，将返回BluetoothGattCallback回调 进入其如下方法
@Override
public void onCharacteristicRead(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic,
int status) {
if (status == BluetoothGatt.GATT_SUCCESS) {
broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
}
}或
使用如下方法，传入特征值，true
mBluetoothGatt.setCharacteristicNotification(characteristic, enabled);
如果成功，将返回BluetoothGattCallback回调 进入其如下方法
@Override
public void onCharacteristicRead(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic,
int status) {
if (status == BluetoothGatt.GATT_SUCCESS) {
broadcastUpdate(ACTION_DATA_AVAILABLE, characteristic);
}
}具体选择哪种方法就要看具体需求了。
3.还有一个很重要的方法，demo没有给出例子的：
mBluetoothGatt.writeCharacteristic(characteristic);
这是向蓝牙设备写入数据，几乎都会用到的。
如果成功，将返回BluetoothGattCallback回调 进入其如下方法
@Override
public void onCharacteristicWrite(BluetoothGatt gatt,
BluetoothGattCharacteristic characteristic,
int status) {
}4. disconnect()；调用BluetoothGatt.disconnect()断开蓝牙连接；
public void disconnect() {
if (mBluetoothAdapter == null || mBluetoothGatt == null) {
Log.w(TAG, "BluetoothAdapter not initialized");
return;
}
mBluetoothGatt.disconnect();
}5.close();关闭蓝牙
/**
* After using a given BLE device, the app must call this method to ensure resources are
* released properly.
*/
public void close() {
if (mBluetoothGatt == null) {
return;
}
mBluetoothGatt.close();
mBluetoothGatt = null;
}
最后，关于Android蓝牙BLE的使用在此结束，我从下载官方demo到一步一步地去理解具体的调用，最后已经算是走通了整个蓝牙开发流程，如果想再深入点的话就要考虑具体的底层实现，和真实项目中怎么去更好地封装！
