android蓝牙源码分析

关键词：蓝牙blueZ  A2DP、SINK、sink_connect、sink_disconnect、sink_suspend、sink_resume、sink_is_connected、sink_get_properties、AUDIO、DBUS
版本：基于android4.2之前版本 bluez
内核：linux/linux3.08
系统：Android/android4.1.3.4
欢迎指正错误，共同学习、共同进步！！

参考网站：

http://blog.csdn.net/u011960402/article/details/17216563
http://www.cnblogs.com/fityme/archive/2013/04/13/3019471.html socket相关
http://hi.baidu.com/wwwkljoel/item/a35e5745d14e02e6bcf45170 setsockopt

一、蓝牙扫描常用的方法：
         蓝牙扫描的可以通过两种途径实现：命令行hciitool扫描；Android界面触发，通过JNI、DUBS下发命令。
1、  命令行hciitool扫描（这部分通过Linux命令操作，跟android没有关系）
通过bluez的tool发送扫描命令，如：hcitoool scan
adb shell 下#hcitool  scan扫描结果

Hcitool扫描逻辑如下所示：

2、Android界面触发，通过JNI、DUBS下发命令：通过android界面点击搜索设备

应用扫描触发逻辑流程：自上而下三种颜色，分别代表应用部分、JNI部分、linux blueZ部分。

二、Hcitool触发逻辑分析
1、hcitool这部分代码比较简单，实现函数
idh.code\external\bluetooth\bluez\tools\hcitool.c代码大致流程如下：

通过所带的参数，找到cmd_scan,进入hci_inquriy。这个函数中创建一个BTPROTO_HCI的socket,通过ioctlHCINQUIRY向内核读取数据，保存返回信息。

2、内核层逻辑：
当然IOCTL只是其中一项。
idh.code\kernel\net\bluetooth\ hci_sock.c

static const struct proto_ops hci_sock_ops = {  
…………  
    .ioctl      = hci_sock_ioctl,  
    .poll       = datagram_poll,  
    .listen     = sock_no_listen,  
…………  
}; 

   它的流程就是构造查询命令，放入命令队列，调度队列来发送命令，其中hci_send_frame后面会讲解，这里关键是命令的发送和数据的收集是分开的，所以它在里面会放弃2s的调度，以此来等待数据的收集，收集的数据放在hdev->inq_cache里面，我们来看看这个数据是如何取得的，如下图所示：

入口点hci_rx_work前面已经详细分析过了，这里就不说了，它里面会根据不同的事件类型做不同的处理，通常情况下，扫描都是带信号强度的扫描，所以走的hci_inquiry_result_with_rssi_evt路线，还有其它几种扫描方式，比如：HCI_EV_INQUIRY_RESULT，HCI_EV_EXTENDED_INQUIRY_RESULT等，处理逻辑都差不多的，里面会hci_inquiry_cache_update来把结果放到hdev->discovery链表里面去，供后面的查询；比如前面调用的inquiry_cache_dump函数就可以从这个链表里面把数据取出来，然后copy到用户层；
三、Android界面触发，通过JNI、DUBS下发命令
整体流程如下所示：

（一）、应用部分：
1、 idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\DeviceListPreferenceFragment.Java

    @Override  
      public boolean onPreferenceTreeClick(PreferenceScreen preferenceScreen,  
          Preference preference) {  
        …………  
          mLocalAdapter.startScanning(true);  
          return true;  
        }  

2、 idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\LocalBluetoothAdapter.java

private final BluetoothAdapter mAdapter;  
 void startScanning(boolean force) {  
        // Only start if we're not already scanning  
        if (!mAdapter.isDiscovering()) {  
            if (!force) {  
                // Don't scan more than frequently than SCAN_EXPIRATION_MS,  
                // unless forced  
                if (mLastScan + SCAN_EXPIRATION_MS > System.currentTimeMillis()) {  
                    return;  
                }  
                // If we are playing music, don't scan unless forced.  
                A2dpProfile a2dp = mProfileManager.getA2dpProfile();  
                if (a2dp != null && a2dp.isA2dpPlaying()) {  
                    return;  
                }  
            }  
            if (mAdapter.startDiscovery()) {  
                mLastScan = System.currentTimeMillis();  
            }  
        }  
}   

3、idh.code\frameworks\base\core\java\android\bluetooth\ BluetoothAdapter .java

    public boolean startDiscovery() {  
        if (getState() != STATE_ON) return false;  
        try {  
            return mService.startDiscovery();  
        } catch (RemoteException e) {Log.e(TAG, "", e);}  
        return false;  
    }  

4、JNI函数的调用idh.code\frameworks\base\core\java\android\server\BluetoothService.java

    private native boolean startDiscoveryNative();//Native函数声明  
    public class BluetoothService extends IBluetooth.Stub {  
        private static final String TAG = "BluetoothService";  
        private static final boolean DBG = true;  
    …………  
    public synchronized boolean startDiscovery() {  
    mContext.enforceCallingOrSelfPermission(BLUETOOTH_ADMIN_PERM,  
            "Need BLUETOOTH_ADMIN permission");  
            if (!isEnabledInternal()) return false;  
            return startDiscoveryNative();  
    }  
    ………………  
    }  

（二）、JNI部分：
1、android_server_BluetoothService.cpp中JNI函数的对照表
idh.code\frameworks\base\core\jni\android_server_BluetoothService.cpp

    static JNINativeMethod sMethods[] = {  
         /* name, signature, funcPtr */  
       ………………  
        {"startDiscoveryNative", "()Z", (void*)startDiscoveryNative},  
    {"stopDiscoveryNative", "()Z", (void *)stopDiscoveryNative},   
    …………  
    }  

2、对应Native函数的实现
这里面有个知识点DBUS，这个后面我们单独去讲解
idh.code\frameworks\base\core\jni\android_server_BluetoothService.cpp

    #define BLUEZ_DBUS_BASE_IFC       "org.bluez"  
    #define DBUS_ADAPTER_IFACE BLUEZ_DBUS_BASE_IFC ".Adapter"//其实DBUS_ADAPTER_IFACE 也就是 org.bluez.Adapter  
    static jboolean startDiscoveryNative(JNIEnv *env, jobject object) {  
      
    ………………  
        /* Compose the command */  
        msg = dbus_message_new_method_call(BLUEZ_DBUS_BASE_IFC,  
                                           get_adapter_path(env, object),  
                                           DBUS_ADAPTER_IFACE, "StartDiscovery");  
    …………  
    }  
    Native函数startDiscoveryNative和字符串StartDiscovery对应。  

（三）、DBUS部分

1、DBUS对应方法的实现，这里跟JNI部分比较类似，也是用了函数结构体对应关系。
idh.code\external\bluetooth\bluez\src\adapter.c

    #define ADAPTER_INTERFACE   "org.bluez.Adapter"  
    static GDBusMethodTable adapter_methods[] = {  
    ………………  
        { "ReleaseSession", "", "", release_session     },  
        { "StartDiscovery", "", "", adapter_start_discovery },  
        { "StopDiscovery",  "", "", adapter_stop_discovery,  
                            G_DBUS_METHOD_FLAG_ASYNC},  
    ………………  
    }  

字符 StartDiscovery 又对应C中的实现函数adapter_start_discovery。
2、adapter_start_discovery的实现
idh.code\external\bluetooth\bluez\src\adapter.c

    static DBusMessage *adapter_start_discovery(DBusConnection *conn,  
                            DBusMessage *msg, void *data)  
    {  
    …………  
        err = start_discovery(adapter);  
        if (err < 0 && err != -EINPROGRESS)  
            return btd_error_failed(msg, strerror(-err));  
      
    done:  
        req = create_session(adapter, conn, msg, 0,  
                    session_owner_exit);  
      
        adapter->disc_sessions = g_slist_append(adapter->disc_sessions, req);  
      
        return dbus_message_new_method_return(msg);  
    }  

3、 start_discovery调用
idh.code\external\bluetooth\bluez\src\adapter.c

const struct btd_adapter_ops *adapter_ops = NULL;  
static int start_discovery(struct btd_adapter *adapter)  
{  
…………  
    pending_remote_name_cancel(adapter);  
    return adapter_ops->start_discovery(adapter->dev_id);  
} 

adapter_ops对应结构体 btd_adapter_ops中对应函数，如下：上面部分就对应到btd_adapter_ops中的hci_ops结构体。
4、btd_adapter_ops中的hci_ops结构体
idh.code\external\bluetooth\bluez\plugins\hciops.c

    static struct btd_adapter_ops hci_ops = {  
    …………  
        .set_powered = hciops_set_powered,  
        .set_discoverable = hciops_set_discoverable,  
        .set_pairable = hciops_set_pairable,  
        .set_limited_discoverable = hciops_set_limited_discoverable,  
        .start_discovery = hciops_start_discovery,  
        .stop_discovery = hciops_stop_discovery,  
        ………………  
        .create_bonding = hciops_create_bonding,  
        .cancel_bonding = hciops_cancel_bonding,  
        .read_local_oob_data = hciops_read_local_oob_data,  
        .add_remote_oob_data = hciops_add_remote_oob_data,  
        .remove_remote_oob_data = hciops_remove_remote_oob_data,  
        .set_link_timeout = hciops_set_link_timeout,  
        .retry_authentication = hciops_retry_authentication,  
    };  

5、hciops_start_discovery函数的实现
idh.code\external\bluetooth\bluez\plugins\hciops.c

    static int hciops_start_discovery(int index)  
    {  
        int adapter_type = get_adapter_type(index);  
      
        switch (adapter_type) {  
        case BR_EDR_LE:  
            return hciops_start_inquiry(index, LENGTH_BR_LE_INQ);  
        case BR_EDR: //蓝牙芯片为2.1+EDR的  
            return hciops_start_inquiry(index, LENGTH_BR_INQ);  
        case LE_ONLY:  
            return hciops_start_scanning(index, TIMEOUT_LE_SCAN);  
        default:  
            return -EINVAL;  
        }  
    }  

6、hciops_start_inquiry
idh.code\external\bluetooth\bluez\plugins\hciops.c

    static int hciops_start_inquiry(int index, uint8_t length)  
    {  
        struct dev_info *dev = &devs[index];  
        uint8_t lap[3] = { 0x33, 0x8b, 0x9e };  
        inquiry_cp inq_cp;  
      
        DBG("hci%d length %u", index, length);  
      
        memset(&inq_cp, 0, sizeof(inq_cp));  
        memcpy(&inq_cp.lap, lap, 3);  
        inq_cp.length = length;  
        inq_cp.num_rsp = 0x00;  
      
        if (hci_send_cmd(dev->sk, OGF_LINK_CTL,  
                OCF_INQUIRY, INQUIRY_CP_SIZE, &inq_cp) < 0)  
            return -errno;  
      
        return 0;  
    }  

7、idh.code\external\bluetooth\bluez\lib\hci.c

    /* HCI functions that require open device  
     * dd - Device descriptor returned by hci_open_dev. */  
    dd = socket(AF_BLUETOOTH, SOCK_RAW, BTPROTO_HCI);  
    int hci_send_cmd(int dd, uint16_t ogf, uint16_t ocf, uint8_t plen, void *param)  
    {  
    ………………  
        if (plen) {  
            iv[2].iov_base = param;  
            iv[2].iov_len  = plen;  
            ivn = 3;  
        }  
      
        while (writev(dd, iv, ivn) < 0) {//writev这里把数据写到socket里面。  
            if (errno == EAGAIN || errno == EINTR)  
                continue;  
            return -1;  
        }  
        return 0;  
    }  

（四）、内核部分：
1、HCI FILTER的设置
HCIsocket的类型为 BTPROTO_HCI。上层调用setsockopt的时候，触发了内核的hci_sock_setsockopt函数的执行，在这里 面设置了socket的filter特性，包括包类型，包括事件类型；

当上层调用setsockopt(sock, SOL_HCI, HCI_FILTER,&flt, sizeof(flt))时，触发相应的内核路径。
idh.code\kernel\net\bluetooth\hci_sock.c

    static const struct proto_ops hci_sock_ops = {  
        .family     = PF_BLUETOOTH,  
        .owner      = THIS_MODULE,  
    …………  
        .shutdown   = sock_no_shutdown,  
        .setsockopt = hci_sock_setsockopt,  
        .getsockopt = hci_sock_getsockopt,  
        .connect    = sock_no_connect,  
    …………  
    };  

idh.code\kernel\net\bluetooth\hci_sock.c

    static int hci_sock_setsockopt(struct socket *sock, int level, int optname, char __user *optval, unsigned int len)  
    {  
    ………………  
        case HCI_FILTER:  
            {  
                struct hci_filter *f = &hci_pi(sk)->filter;  
      
                uf.type_mask = f->type_mask;  
                uf.opcode    = f->opcode;  
                uf.event_mask[0] = *((u32 *) f->event_mask + 0);  
                uf.event_mask[1] = *((u32 *) f->event_mask + 1);  
            }  
        ………………  
    }

内核这部分就比较统一的数据，通过hci_send_cmd把命令发出去， HCI_FILTER 这个地方的处理还没理解，后面补充 。
Writev函数通过socket把数据写下去，经过VFS层，调用到内核空间的sendmsg函数。

（五）、EVENT返回状态

Controller收到查询命令后，返回一个命令状态
1、cmd_status
idh.code\external\bluetooth\bluez\plugins\hciops.c

 switch (eh->evt) {  
    case EVT_CMD_STATUS:  
        cmd_status(index, ptr);  
        break;  
static inline void cmd_status(int index, void *ptr)  
{  
    evt_cmd_status *evt = ptr;  
    uint16_t opcode = btohs(evt->opcode);  
  
    if (opcode == cmd_opcode_pack(OGF_LINK_CTL, OCF_INQUIRY))//如果是inquriy做特殊处理；  
        cs_inquiry_evt(index, evt->status);  
}  

2、cs_inquiry_evt的实现 idh.code\external\bluetooth\bluez\plugins\hciops.c

    static inline void cs_inquiry_evt(int index, uint8_t status)  
    {  
        if (status) {//错误信息  
            error("Inquiry Failed with status 0x%02x", status);  
            return;  
        }  
      
        set_state(index, DISCOV_INQ);//设置状态为INQ，向上层回复discoverying的property change  
    }  

3、设置不同的DISCOV 状态 idh.code\external\bluetooth\bluez\plugins\hciops.c

    static void set_state(int index, int state)  
    {  
        ………………  
        switch (dev->discov_state) {  
        case DISCOV_HALTED://停止发现;  
            if (adapter_get_state(adapter) == STATE_SUSPENDED)  
                return;  
      
            if (is_resolvname_enabled() &&  
                        adapter_has_discov_sessions(adapter))  
                adapter_set_state(adapter, STATE_RESOLVNAME);  
            else  
                adapter_set_state(adapter, STATE_IDLE);  
            break;  
        case DISCOV_INQ:  
        case DISCOV_SCAN://扫描发现；  
            adapter_set_state(adapter, STATE_DISCOV);  
            break;  
        }  
    }  

4、设置adapter的状态 idh.code\external\bluetooth\bluez\src\adapter.c

    idh.code\external\bluetooth\bluez\src\adapter.c  
    #define ADAPTER_INTERFACE   "org.bluez.Adapter"  
    void adapter_set_state(struct btd_adapter *adapter, int state)  
    {  
    …………  
        case STATE_DISCOV:  
            discov_active = TRUE;  
    //向上层回复discovering的property change  
            emit_property_changed(connection, path,  
                        ADAPTER_INTERFACE, "Discovering",  
                        DBUS_TYPE_BOOLEAN, &discov_active);  
            break;  
    …………  
    }  

emit_property_changed发送PropertyChanged的消息，消息内容为 Discovering。通知上层BluetoothEventLoop进行Discovering。
5、emit_property_changed发送Discovering消息的实现  idh.code\external\bluetooth\bluez\src\dbus-common.c
这部分涉及到DBUS内容

    dbus_bool_t emit_property_changed(DBusConnection *conn,  
                        const char *path,  
                        const char *interface,  
                        const char *name,  
                        int type, void *value)  
    {  
        DBusMessage *signal;  
        DBusMessageIter iter;  
        signal = dbus_message_new_signal(path, interface, "PropertyChanged"); // 创建消息对象并标识路径   
        if (!signal) {  
            error("Unable to allocate new %s.PropertyChanged signal",  
                    interface);  
            return FALSE;  
        }  
        dbus_message_iter_init_append(signal, &iter);//把信号相对应的参数压进去  
        dbus_message_iter_append_basic(&iter, DBUS_TYPE_STRING, &name);//申请一个首地址，把前面压入的参数传入这个首地址      
    append_variant(&iter, type, value);//  
        return g_dbus_send_message(conn, signal);//启动发送调用，并释放发送相关消息信息  
    }  

6、DBUS消息接收的实现 idh.code\frameworks\base\core\jni\android_server_BluetoothEventLoop.cpp

    // Called by dbus during WaitForAndDispatchEventNative()  
    static DBusHandlerResult event_filter(DBusConnection *conn, DBusMessage *msg,  
                                          void *data) {  
    …………  
    else if (dbus_message_is_signal(msg, "org.bluez.Adapter", "PropertyChanged")) {  
            jobjectArray str_array = parse_adapter_property_change(env, msg);//（1）、对收到消息的解析  
            if (str_array != NULL) {  
                /* Check if bluetoothd has (re)started, if so update the path. */  
                jstring property =(jstring) env->GetObjectArrayElement(str_array, 0);  
                const char *c_property = env->GetStringUTFChars(property, NULL);  
                if (!strncmp(c_property, "Powered", strlen("Powered"))) {  
                    jstring value =  
                        (jstring) env->GetObjectArrayElement(str_array, 1);  
                    const char *c_value = env->GetStringUTFChars(value, NULL);  
                    if (!strncmp(c_value, "true", strlen("true")))  
                        nat->adapter = get_adapter_path(nat->conn);  
                    env->ReleaseStringUTFChars(value, c_value);  
                }  
                env->ReleaseStringUTFChars(property, c_property);  
      
                env->CallVoidMethod(nat->me,  
                                  method_onPropertyChanged,//（2）、  
    method_onPropertyChanged NATVIE函数的实现  
                                  str_array);  
            } else LOG_AND_FREE_DBUS_ERROR_WITH_MSG(&err, msg);  
            goto success;  
    }  

（1）、对收到消息的解析 idh.code\frameworks\base\core\jni\android_bluetooth_common.cpp

    jobjectArray parse_adapter_property_change(JNIEnv *env, DBusMessage *msg) {  
        return parse_property_change(env, msg, (Properties *) &adapter_properties,  
                        sizeof(adapter_properties) / sizeof(Properties));  
    }  

针对org.bluez.Adapter不同的消息类型
idh.code\frameworks\base\core\jni\android_bluetooth_common.cpp

    static Properties adapter_properties[] = {  
        {"Address", DBUS_TYPE_STRING},  
        {"Name", DBUS_TYPE_STRING},  
        {"Class", DBUS_TYPE_UINT32},  
        {"Powered", DBUS_TYPE_BOOLEAN},  
        {"Discoverable", DBUS_TYPE_BOOLEAN},  
        {"DiscoverableTimeout", DBUS_TYPE_UINT32},  
        {"Pairable", DBUS_TYPE_BOOLEAN},  
        {"PairableTimeout", DBUS_TYPE_UINT32},  
        {"Discovering", DBUS_TYPE_BOOLEAN},  
        {"Devices", DBUS_TYPE_ARRAY},  
        {"UUIDs", DBUS_TYPE_ARRAY},  
    };  

（2）、method_onPropertyChanged NATVIE函数的实现 idh.code\frameworks\base\core\jni\android_server_BluetoothEventLoop.cpp

    static void classInitNative(JNIEnv* env, jclass clazz) {  
        ALOGV("%s", __FUNCTION__);  
    #ifdef HAVE_BLUETOOTH  
        method_onPropertyChanged = env->GetMethodID(clazz, "onPropertyChanged",  
                                                    "([Ljava/lang/String;)V");  
    method_onDevicePropertyChanged = env->GetMethodID(clazz,  
     "onDevicePropertyChanged","(Ljava/lang/String;[Ljava/lang/String;)V");  
    …………  
    }  

7、JNI调用 onPropertyChanged 对应JAVA的实现，在BluetoothEventLoop.java
idh.code\frameworks\base\core\java\android\server\BluetoothEventLoop.java中

    
   private static native void classInitNative();  
    /*package*/ void onPropertyChanged(String[] propValues) {  
     ………………  
            log("Property Changed: " + propValues[0] + " : " + propValues[1]);  
            String name = propValues[0];  
            if (name.equals("Name")) {//获取蓝牙名字；  
                …………  
            } else if (name.equals("Pairable") || name.equals("Discoverable")) {//配对；  
               ………………  
            } else if (name.equals("Discovering")) {//扫描查询；  
                Intent intent;  
                adapterProperties.setProperty(name, propValues[1]);  
                if (propValues[1].equals("true")) {  
                    intent = new Intent(BluetoothAdapter.ACTION_DISCOVERY_STARTED);  
                } else {  
                    // Stop the discovery.  
                    mBluetoothService.cancelDiscovery();  
                    intent = new Intent(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);  
                }  
                mContext.sendBroadcast(intent, BLUETOOTH_PERM);  
            } else if (name.equals("Devices") || name.equals("UUIDs")) {//Devices、UUID的获取；  
            ………………  
            } else if (name.equals("Powered")) {//蓝牙打开、关闭；  
                mBluetoothState.sendMessage(BluetoothAdapterStateMachine.POWER_STATE_CHANGED,  
                    propValues[1].equals("true") ? new Boolean(true) : new Boolean(false));  
            } else if (name.equals("DiscoverableTimeout")) {  
                adapterProperties.setProperty(name, propValues[1]);  
            }  
        } 
  

（1）、看到这份log我们也许会更明白其他功能的由来：

    D BluetoothEventLoop: Property Changed: Powered : true  
    D BluetoothEventLoop: Property Changed: Pairable : true  
    D BluetoothEventLoop: Property Changed: Class : 5898764  
    D BluetoothEventLoop: Property Changed: Pairable : true  
    D BluetoothEventLoop: Property Changed: Discoverable : false  
    D BluetoothEventLoop: Property Changed: Discovering : true  
    D BluetoothEventLoop: Property Changed: Discovering : false  
    D BluetoothEventLoop: Property Changed: Devices : 1  
    D BluetoothEventLoop: Device property changed: 94:20:53:01:15:90 property: Connected value: true  
    D BluetoothEventLoop: Device property changed: 94:20:53:01:15:90 property: Paired value: true  
    D BluetoothEventLoop: Device property changed: 94:20:53:01:15:90 property: UUIDs value: 4  

（2）、下面我们重点分析Discovering这部分：
idh.code\frameworks\base\core\java\android\server\BluetoothEventLoop.java

    else if (name.equals("Discovering")) {  
                Intent intent;  
                adapterProperties.setProperty(name, propValues[1]);  
                if (propValues[1].equals("true")) {//开始扫描  
                    intent = new Intent(BluetoothAdapter.ACTION_DISCOVERY_STARTED);//  
                } else {  
                    // Stop the discovery. //停止扫描  
                    mBluetoothService.cancelDiscovery();  
                    intent = new Intent(BluetoothAdapter.ACTION_DISCOVERY_FINISHED);  
                }  
                mContext.sendBroadcast(intent, BLUETOOTH_PERM);  
            }  
    这样就可以通过broadcast发送ACTION_DISCOVERY_STARTED广播，注册的receiver来响应了。  

8、ACTION_DISCOVERY_STARTED\ACTION_DISCOVERY_FINISHED的receiver分析
从代码中我们可以看到这个action一共有两个receiver，一个是静态注册的 BluetoothDiscoveryReceiver,一个是动态注册是 ScanningStateChangedHandler。
（1）、BluetoothDiscoveryReceiver：这个receiver是在settings中的Androidmanifest中静态注册的。用途：主要用于获取扫描开始和终止的时间。
idh.code\packages\apps\Settings\AndroidManifest.xml

1）、ACTION_DISCOVERY_STARTED、ACTION_DISCOVERY_FINISHED和AndroidManifest.xml文件的联系
idh.code\frameworks\base\core\java\android\bluetooth\BluetoothAdapter.java

    public final class BluetoothAdapter {  
        private static final String TAG = "BluetoothAdapter";  
    private static final boolean DBG = false;  
    …………  
        public static final String ACTION_DISCOVERY_STARTED =  
                "android.bluetooth.adapter.action.DISCOVERY_STARTED";  
        public static final String ACTION_DISCOVERY_FINISHED =  
                "android.bluetooth.adapter.action.DISCOVERY_FINISHED";  
    …………  
    }  

2）、BluetoothAdapter，蓝牙适配器，直到我们建立bluetoothSocket连接之前，都要不断操作它。
BluetoothAdapter中的动作常量

ACTION_DISCOVERY_FINISHED	已完成蓝牙搜索
ACTION_DISCOVERY_STARTED	已经开始搜索蓝牙设备
ACTION_LOCAL_NAME_CHANGED	更改蓝牙的名字
ACTION_REQUEST_DISCOVERABLE	请求能够被搜索
ACTION_REQUEST_ENABLE	请求启动蓝牙
ACTION_SCAN_MODE_CHANGED	扫描模式已经改变
ACTION_STATE_CHANGED	状态已改变
ACTION_CONNECTION_STATE_CHANGED

3）、收到广播后函数实现，开始扫描
Main log中显示的log为DISCOVERY_STARTED
D BluetoothDiscoveryReceiver: Received:android.bluetooth.adapter.action.DISCOVERY_STARTED
HCI log 中

idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\BluetoothDiscoveryReceiver.java这个文件中就一个函数，还是比简单

    public final class BluetoothDiscoveryReceiver extends BroadcastReceiver {  
        private static final String TAG = "BluetoothDiscoveryReceiver";  
        private static final boolean DEBUG = Debug.isDebug();  
      
        @Override  
        public void onReceive(Context context, Intent intent) {  
            String action = intent.getAction();  
            if (DEBUG) Log.d(TAG, "Received: " + action);  
      
            if (action.equals(BluetoothAdapter.ACTION_DISCOVERY_STARTED) ||  
                    action.equals(BluetoothAdapter.ACTION_DISCOVERY_FINISHED)) {      
    //共享时间戳，扫描开始和结束的时间。   
       LocalBluetoothPreferences.persistDiscoveringTimestamp(context);  
            }  
        }  
    }  

ScanningStateChangedHandler的注册及用途，要用于开始扫描，和扫描显示界面的控制。
这个receiver是在idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\BluetoothEventManager.java动态注册的，如下：

    BluetoothEventManager(LocalBluetoothAdapter adapter,  
                CachedBluetoothDeviceManager deviceManager, Context context) {  
    mLocalAdapter = adapter;  
    …………  
    // Bluetooth on/off broadcasts  
     addHandler(BluetoothAdapter.ACTION_STATE_CHANGED, new AdapterStateChangedHandler());  
      
    // Discovery broadcastsaddHandler(BluetoothAdapter.ACTION_DISCOVERY_STARTED, new ScanningStateChangedHandler(true));  
            addHandler(BluetoothAdapter.ACTION_DISCOVERY_FINISHED, new ScanningStateChangedHandler(false));  
    …………  
    }  

（1）、ScanningStateChangedHandler函数实现如下：idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\BluetoothEventManager.java

private class ScanningStateChangedHandler implements Handler {  
        private final boolean mStarted;  
  
        ScanningStateChangedHandler(boolean started) {  
            mStarted = started;  
        }  
        public void onReceive(Context context, Intent intent,  
                BluetoothDevice device) {  
            synchronized (mCallbacks) {//1)、调用注册的callback  
中的onScanningStateChanged函数。  
                for (BluetoothCallback callback : mCallbacks) {  
                    callback.onScanningStateChanged(mStarted);  
                }  
            }  
//2）、这个函数就是把上次扫描到设备、和之前的设备做相应处理；  
            mDeviceManager.onScanningStateChanged(mStarted);  
            LocalBluetoothPreferences.persistDiscoveringTimestamp(context);  
        }  
}  

1）、调用注册的callback中的callback.onScanningStateChanged(mStarted)函数。
idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\DeviceListPreferenceFragment.java

    public void onScanningStateChanged(boolean started) {  
        if (started == false) {//《1》、如果扫描结束；  
            removeOutOfRangeDevices();  
        }  
        updateProgressUi(started);// 《2》、UI显示小圆圈扫描；  

《1》、如果扫描结束；removeOutOfRangeDevices();
idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\DeviceListPreferenceFragment.java

    private void removeOutOfRangeDevices() {  
        Collection cachedDevices =  
                mLocalManager.getCachedDeviceManager().getCachedDevicesCopy();  
        for (CachedBluetoothDevice cachedDevice : cachedDevices) {  
             if (cachedDevice.getBondState() == BluetoothDevice.BOND_NONE &&  
                 cachedDevice.isVisible() == false) {  
                 BluetoothDevicePreference preference = mDevicePreferenceMap.get(cachedDevice);  
                 if (preference != null) {  
                     mDeviceListGroup.removePreference(preference);  
                 }  
                 mDevicePreferenceMap.remove(cachedDevice);  
              }  
         }  
    }  

《2》、UI显示小圆圈扫描，updateProgressUi(started)；如下图所示：

idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\DeviceListPreferenceFragment.java

    private void updateProgressUi(boolean start) {  
        if (mDeviceListGroup instanceof ProgressCategory) {  
            ((ProgressCategory) mDeviceListGroup).setProgress(start);  
        }  
    }  

2）、这部分的作用，开始扫描，不显示列表中内容，或把之前列表中没扫描到的设备清除
mDeviceManager.onScanningStateChanged(mStarted);
idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\CachedBluetoothDevice.java

    private void updateProgressUi(boolean start) {  
        if (mDeviceListGroup instanceof ProgressCategory) {  
            ((ProgressCategory) mDeviceListGroup).setProgress(start);  
        }  
    }  
    2）、这部分的作用，开始扫描，不显示列表中内容，或把之前列表中没扫描到的设备清除  
    mDeviceManager.onScanningStateChanged(mStarted);  
    idh.code\packages\apps\Settings\src\com\android\settings\bluetooth\ CachedBluetoothDevice.java  
        public synchronized void onScanningStateChanged(boolean started) {  
            // If starting a new scan, clear old visibility  
            // Iterate in reverse order since devices may be removed.  
            //如果开始新的扫描，清除旧的能见设备，迭代反序因为有的设备可能被删除  
            for (int i = mCachedDevices.size() - 1; i >= 0; i--) {  
                CachedBluetoothDevice cachedDevice = mCachedDevices.get(i);  
                if (started) {//如果扫描开始就不显示；  
                    cachedDevice.setVisible(false);  
                } else {//对扫描的结果作出判断，如果之前扫描过，这次没有扫描到，就移除列表。  
                    if (cachedDevice.getBondState() == BluetoothDevice.BOND_NONE &&  
                            cachedDevice.isVisible() == false) {  
                        mCachedDevices.remove(cachedDevice);  
                    }  
                }  
            }  
        }  

                                                      ~~~~~~~~~    End      ~~~~~~~