Android BLE 总结－源码篇(BluetoothLeAdvertiser)

在做Android BLE的应用程序时，我们发出广播数据是调用BluetoothLeAdvertiser的startAdvertising方法，如下所示：

mBluetoothLeAdvertiser.startAdvertising(advertiseSettings,
                advertiseData, myAdvertiseCallback);

那么我打算写的BLE总结之源码篇就以此为线索来分析Android BLE　FrameWork方面的东西。

 public void startAdvertising(AdvertiseSettings settings,
            AdvertiseData advertiseData, final AdvertiseCallback callback) {
        startAdvertising(settings, advertiseData, null, callback);
    }
public void startAdvertising(AdvertiseSettings settings,
            AdvertiseData advertiseData, AdvertiseData scanResponse,
            final AdvertiseCallback callback) {
        synchronized (mLeAdvertisers) {

//该check只是检查mBluetoothAdater是否为null和其状态是否为State_ON

            BluetoothLeUtils.checkAdapterStateOn(mBluetoothAdapter);
            if (callback == null) {
                throw new IllegalArgumentException("callback cannot be null");
            }

            if (!mBluetoothAdapter.isMultipleAdvertisementSupported() &&
                    !mBluetoothAdapter.isPeripheralModeSupported()) {//是否支持广播和作为外围设备
                postStartFailure(callback,
                        AdvertiseCallback.ADVERTISE_FAILED_FEATURE_UNSUPPORTED);
                return;
            }
            boolean isConnectable = settings.isConnectable();
            if (totalBytes(advertiseData, isConnectable) > MAX_ADVERTISING_DATA_BYTES ||
                    totalBytes(scanResponse, false) > MAX_ADVERTISING_DATA_BYTES) {
                postStartFailure(callback, AdvertiseCallback.ADVERTISE_FAILED_DATA_TOO_LARGE);
                return;
            }
            if (mLeAdvertisers.containsKey(callback)) {
                postStartFailure(callback, AdvertiseCallback.ADVERTISE_FAILED_ALREADY_STARTED);
                return;
            }
            IBluetoothGatt gatt;
            try {
                gatt = mBluetoothManager.getBluetoothGatt();
            } catch (RemoteException e) {
                Log.e(TAG, "Failed to get Bluetooth gatt - ", e);
                postStartFailure(callback, AdvertiseCallback.ADVERTISE_FAILED_INTERNAL_ERROR);
                return;
            }
            AdvertiseCallbackWrapper wrapper = new AdvertiseCallbackWrapper(callback, advertiseData,
                    scanResponse, settings, gatt);
            wrapper.startRegisteration();
        }
    }

大家可以看到在startAdvertising内部，首先经过了一系列的判断，然后包装了一个叫作AdvertiseCallbackWrapper的类来做发广播数据的行为。

我们先看一下startAdvertising内部都是做了哪些判断：
1.判断蓝牙是否已经打开，否则抛出异常。

2.判断回调callback是否为空

3.判断当前设备是否支持广播数据和作为外围设备

4.判断广播数据包的长度是否超过了31字节

5.判断广播是否已经开始

经过了这５步初步的判断，下面来到了最重要的地方，mBluetoothManager.getBluetoothGatt();获取一个引用，最终的发送广播和停止广播都是通过这个引用来进行实现的。这里不进行展开，因为本文主要是对BluetoothLeAdvertiser的解读。

下面我们就来看看刚才提到的AdvertiseCallbackWrapper，代码如下：

 /**
     * Bluetooth GATT interface callbacks for advertising.
     */
    private class AdvertiseCallbackWrapper extends BluetoothGattCallbackWrapper {
        private static final int LE_CALLBACK_TIMEOUT_MILLIS = 2000;
        private final AdvertiseCallback mAdvertiseCallback;
        private final AdvertiseData mAdvertisement;
        private final AdvertiseData mScanResponse;
        private final AdvertiseSettings mSettings;
        private final IBluetoothGatt mBluetoothGatt;
        // mClientIf 0: not registered
        // -1: advertise stopped or registration timeout
        // >0: registered and advertising started
        private int mClientIf;
        private boolean mIsAdvertising = false;
        public AdvertiseCallbackWrapper(AdvertiseCallback advertiseCallback,
                AdvertiseData advertiseData, AdvertiseData scanResponse,
                AdvertiseSettings settings,
                IBluetoothGatt bluetoothGatt) {
            mAdvertiseCallback = advertiseCallback;
            mAdvertisement = advertiseData;
            mScanResponse = scanResponse;
            mSettings = settings;
            mBluetoothGatt = bluetoothGatt;
            mClientIf = 0;
        }
        public void startRegisteration() {
            synchronized (this) {
                if (mClientIf == -1) return;//这个就不解释了
                try {
                    UUID uuid = UUID.randomUUID();
                    mBluetoothGatt.registerClient(new ParcelUuid(uuid), this);//注册
                    wait(LE_CALLBACK_TIMEOUT_MILLIS);//等待２秒,在过程中会依次回调onClientRegistered和onMultiAdvertiseCallback
                } catch (InterruptedException | RemoteException e) {
                    Log.e(TAG, "Failed to start registeration", e);
                }

//注册成功并且广播成功，加入广播缓存，以callback为key的Hashmap,callback为用户自己定义的Callback

                if (mClientIf > 0 && mIsAdvertising) {
                    mLeAdvertisers.put(mAdvertiseCallback, this);
                } else if (mClientIf <= 0) {//注册失败
                    // Registration timeout, reset mClientIf to -1 so no subsequent operations can
                    // proceed.
                    if (mClientIf == 0) mClientIf = -1;
                    // Post internal error if registration failed.
                    postStartFailure(mAdvertiseCallback,
                            AdvertiseCallback.ADVERTISE_FAILED_INTERNAL_ERROR);
                } else {//注册成功但广播开启失败
                    // Unregister application if it's already registered but advertise failed.
                    try {
                        mBluetoothGatt.unregisterClient(mClientIf);
                        mClientIf = -1;
                    } catch (RemoteException e) {
                        Log.e(TAG, "remote exception when unregistering", e);
                    }
                }
            }
        }
        public void stopAdvertising() {
            synchronized (this) {
                try {
                    mBluetoothGatt.stopMultiAdvertising(mClientIf);
                    wait(LE_CALLBACK_TIMEOUT_MILLIS);
                } catch (InterruptedException | RemoteException e) {
                    Log.e(TAG, "Failed to stop advertising", e);
                }
                // Advertise callback should have been removed from LeAdvertisers when
                // onMultiAdvertiseCallback was called. In case onMultiAdvertiseCallback is never
                // invoked and wait timeout expires, remove callback here.
                if (mLeAdvertisers.containsKey(mAdvertiseCallback)) {
                    mLeAdvertisers.remove(mAdvertiseCallback);
                }
            }
        }
        /**
         * Application interface registered - app is ready to go
         */
        @Override
        public void onClientRegistered(int status, int clientIf) {
            Log.d(TAG, "onClientRegistered() - status=" + status + " clientIf=" + clientIf);
            synchronized (this) {
                if (status == BluetoothGatt.GATT_SUCCESS) {
                    try {
                        if (mClientIf == -1) {//在２秒内未完成注册，超时
                            // Registration succeeds after timeout, unregister client.
                            mBluetoothGatt.unregisterClient(clientIf);
                        } else {//完成注册，并开始广播
                            mClientIf = clientIf;
                            mBluetoothGatt.startMultiAdvertising(mClientIf, mAdvertisement,
                                    mScanResponse, mSettings);
                        }
                        return;
                    } catch (RemoteException e) {
                        Log.e(TAG, "failed to start advertising", e);
                    }
                }
                // Registration failed.
                mClientIf = -1;
                notifyAll();
            }
        }
        @Override
        public void onMultiAdvertiseCallback(int status, boolean isStart,
                AdvertiseSettings settings) {
            synchronized (this) {
                if (isStart) {//广播成功时的回调
                    if (status == AdvertiseCallback.ADVERTISE_SUCCESS) {
                        // Start success
                        mIsAdvertising = true;
                        postStartSuccess(mAdvertiseCallback, settings);
                    } else {
                        // Start failure.
                        postStartFailure(mAdvertiseCallback, status);
                    }
                } else {//stop 时的回调，用来反注册和清除缓存的callback
                    // unregister client for stop.
                    try {
                        mBluetoothGatt.unregisterClient(mClientIf);
                        mClientIf = -1;
                        mIsAdvertising = false;
                        mLeAdvertisers.remove(mAdvertiseCallback);
                    } catch (RemoteException e) {
                        Log.e(TAG, "remote exception when unregistering", e);
                    }
                }
                notifyAll();
            }
        }
    }
    private void postStartFailure(final AdvertiseCallback callback, final int error) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                callback.onStartFailure(error);
            }
        });
    }
    private void postStartSuccess(final AdvertiseCallback callback,
            final AdvertiseSettings settings) {
        mHandler.post(new Runnable() {
            @Override
            public void run() {
                callback.onStartSuccess(settings);
            }
        });
    }

AdvertiseCallbackWrapper的成员变量mClientIf非常重要，在广播发送和停止的过程中起着重要的作用。这里先简单的记住该属性的以下特征：

mClientIf=0——>未注册

mClinetIf=-1——>广播停止或注册超时

mClientIf>0——>已注册并且已经广播成功

mClientIf默认值为0

这时我们追踪到startRegisteration这个方法了，该方法里面调用了registerClient方法，经过IPC通信后会回调到onClientRegistered方法，继续调用到了startMultiAdvertising方法，接着触发onMultiAdvertiseCallback，成功发送广播后，将该AdvertiseCallbackWrapper对象加入mLeAdvertisers。

这里我们需要注意和了解以下几点：

1.在调用startRegisteration的2秒的时间内，如果没有注册成功且广播成功，这次广播数据的行为均为失败。

2.即使2秒之后onClientRegistered回调，也将视为注册未成功，并进行解注册操作。

startAdvertising方法就到这，至于更底层的细节后续的文章会展开，下面我们看一下其对应的stopAdvertising方法

  /**
     * Stop Bluetooth LE advertising. The {@code callback} must be the same one use in
     * {@link BluetoothLeAdvertiser#startAdvertising}.
     * <p>
     * Requires {@link android.Manifest.permission#BLUETOOTH_ADMIN} permission.
     *
     * @param callback {@link AdvertiseCallback} identifies the advertising instance to stop.
     */
    public void stopAdvertising(final AdvertiseCallback callback) {
        synchronized (mLeAdvertisers) {
            if (callback == null) {
                throw new IllegalArgumentException("callback cannot be null");
            }
            AdvertiseCallbackWrapper wrapper = mLeAdvertisers.get(callback);
            if (wrapper == null) return;
            wrapper.stopAdvertising();
        }
    }

大家可以看到，stopAdvertising方法内部是调用AdvertiseCallbackWrapper.stopAdvertising方法。这里必须注意stopAdvertising方法的callback必须和start时传入的callback参数是同一个。否则在mLeAdvertisers缓存里是找不到相应的AdvertiseCallbackWrapper的实例的，就无法正常停止广播。
转载请注明：http://blog.csdn.net/android_jiangjun/article/details/77946857