Android 蓝牙开发——查找附近设备（四）
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。