Android蓝牙服务查找附近设备分析探索
作者:c小旭
一、APP端调用
1、注册广播监听查找结果
//蓝牙发现设备和查找结束广播 IntentFilter intentFilter = new IntentFilter(); intentFilter.addAction(BluetoothDevice.ACTION_FOUND); intentFilter.addAction(BluetoothAdapter.ACTION_DISCOVERY_FINISHED); registerReceiver(btReceiver, intentFilter); BroadcastReceiver btReceiver = new BroadcastReceiver() { @Override public void onReceive(Context context, Intent intent) { if (BluetoothDevice.ACTION_FOUND.equals(intent.getAction())) { BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE); if (device != null) { //这里收到的是单条设备信息,可以放到List中进行刷新列表 //设备名称:device.getName() //设备地址:device.getAddress() if(device.getBondState() == BluetoothDevice.BOND_BONDED) { //已配对设备 } } } else if (BluetoothAdapter.ACTION_DISCOVERY_FINISHED.equals(intent.getAction())) { //查找结束 } } };
2、开始查找附近设备
btAdapter.startDiscovery();
3、异常处理
上面代码无法接收到 BluetoothDevice.ACTION_FOUND 广播,查找资料发现 Android 6.0 后需要增加两个权限并且需要动态申请。
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION"/>
if(Build.VERSION.SDK_INT>=Build.VERSION_CODES.M && checkSelfPermission(Manifest.permission.ACCESS_FINE_LOCATION)!= PackageManager.PERMISSION_GRANTED) {//请求权限 requestPermissions(new String[]{Manifest.permission.ACCESS_FINE_LOCATION},1); }
这里的权限动态申请就简单处理一下,不做详细介绍了。
另一个问题是收到发现设备广播数据,很多数据的 getName() 为 null,这里还需要做一些判空处理。
二、查找设备源码分析
1、BluetoothAdapter.startDiscovery()
private IBluetooth mService; public boolean startDiscovery() { if (getState() != STATE_ON) { return false; } try { mServiceLock.readLock().lock(); if (mService != null) { return mService.startDiscovery(mAttributionSource); } } catch (RemoteException e) { Log.e(TAG, "", e); } finally { mServiceLock.readLock().unlock(); } return false; }
可以看到这里直接调用 mService.startDiscovery(),IBluetooth 的实现类为 AdapterService,相较于蓝牙开关功能,省去了调用 BluetoothManagerService 的部分。
2、AdapterService.startDiscovery()
public boolean startDiscovery(AttributionSource attributionSource) { AdapterService service = getService(); if (service == null || !callerIsSystemOrActiveUser(TAG, "startDiscovery")) { return false; } if (!Utils.checkScanPermissionForDataDelivery( service, attributionSource, "Starting discovery.")) { return false; } return service.startDiscovery(attributionSource); } boolean startDiscovery(AttributionSource attributionSource) { UserHandle callingUser = UserHandle.of(UserHandle.getCallingUserId()); debugLog("startDiscovery"); String callingPackage = attributionSource.getPackageName(); mAppOps.checkPackage(Binder.getCallingUid(), callingPackage); boolean isQApp = Utils.isQApp(this, callingPackage); boolean hasDisavowedLocation = Utils.hasDisavowedLocationForScan(this, attributionSource, mTestModeEnabled); String permission = null; if (Utils.checkCallerHasNetworkSettingsPermission(this)) { permission = android.Manifest.permission.NETWORK_SETTINGS; } else if (Utils.checkCallerHasNetworkSetupWizardPermission(this)) { permission = android.Manifest.permission.NETWORK_SETUP_WIZARD; } else if (!hasDisavowedLocation) { if (isQApp) { if (!Utils.checkCallerHasFineLocation(this, attributionSource, callingUser)) { return false; } permission = android.Manifest.permission.ACCESS_FINE_LOCATION; } else { if (!Utils.checkCallerHasCoarseLocation(this, attributionSource, callingUser)) { return false; } permission = android.Manifest.permission.ACCESS_COARSE_LOCATION; } } synchronized (mDiscoveringPackages) { mDiscoveringPackages.add(new DiscoveringPackage(callingPackage, permission, hasDisavowedLocation)); } return startDiscoveryNative(); }
这里可以看到权限验证相关的内容。最后调用 startDiscoveryNative() 进入 JNI 层,在com_android_bluetooth_btservice_AdapterService.cpp文件中,调用startDiscoveryNative方法。
3、startDiscoveryNative()
源码位置:packages/apps/Bluetooth/jni/com_android_bluetooth_btservice_AdapterService.cpp
static jboolean startDiscoveryNative(JNIEnv* env, jobject obj) { ALOGV("%s", __func__); if (!sBluetoothInterface) return JNI_FALSE; int ret = sBluetoothInterface->start_discovery(); return (ret == BT_STATUS_SUCCESS) ? JNI_TRUE : JNI_FALSE; }
4、start_discovery() 扫描入口
源码位置:system/bt/btif/src/bluetooth.cc
static int start_discovery(void) { if (!interface_ready()) return BT_STATUS_NOT_READY; do_in_main_thread(FROM_HERE, base::BindOnce(btif_dm_start_discovery)); return BT_STATUS_SUCCESS; }
5、btif_dm_start_discovery() 配置参数
源码位置:/system/bt/btif/src/btif_dm.cc
设备管理(DM)相关的功能
void btif_dm_start_discovery(void) { ...... /* Will be enabled to true once inquiry busy level has been received */ btif_dm_inquiry_in_progress = false; /* find nearby devices */ BTA_DmSearch(btif_dm_search_devices_evt, is_bonding_or_sdp()); }
6、BTA_DmSearch() 搜索对等蓝牙设备
源码位置:/system/bt/bta/dm/bta_dm_api.cc
它执行查询并获取设备的远程名称。
void BTA_DmSearch(tBTA_DM_SEARCH_CBACK* p_cback, bool is_bonding_or_sdp) { tBTA_DM_API_SEARCH* p_msg = (tBTA_DM_API_SEARCH*)osi_calloc(sizeof(tBTA_DM_API_SEARCH)); /* Queue request if a device is bonding or performing service discovery */ if (is_bonding_or_sdp) { p_msg->hdr.event = BTA_DM_API_QUEUE_SEARCH_EVT; } else { p_msg->hdr.event = BTA_DM_API_SEARCH_EVT; } p_msg->p_cback = p_cback; bta_sys_sendmsg(p_msg); }
7、bta_sys_sendmsg() 发送扫描消息
源码位置:/system/bt/bta/sys/bta_sys_main.cc
向 BTU TASK 发送扫描消息,由蓝牙设备管理模块处理。
void bta_sys_sendmsg(void* p_msg) { if (do_in_main_thread( FROM_HERE, base::Bind(&bta_sys_event, static_cast<BT_HDR_RIGID*>(p_msg))) != BT_STATUS_SUCCESS) { LOG(ERROR) << __func__ << ": do_in_main_thread failed"; } }
这里调用的是 do_in_main_thread() 方法,这个方法其实在 4 中已经调用过一次。这个方法只是返回一个状态。
位置:/system/bt/stack/btu/btu_task.cc
bt_status_t do_in_main_thread(const base::Location& from_here, base::OnceClosure task) { if (!main_thread.DoInThread(from_here, std::move(task))) { LOG(ERROR) << __func__ << ": failed from " << from_here.ToString(); return BT_STATUS_FAIL; } return BT_STATUS_SUCCESS; }
BTU TASK收到消息后,调用 bta_dm_main.c 的(用于DM的状态机事件处理函数) bta_dm_search_sm_execute() 执行状态切换和 inquiry 流程。这里就不往下分析了。
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