本文主要內容是藍芽手機音訊的連線、斷開流程分析，對應藍芽HFP profile。

該文章是基於Android原始碼4.3的

HFP (Hands-free Profile)，讓藍芽裝置（如藍芽耳機）可以控制電話，如接聽、結束通話、拒接、語音撥號等，拒接、語音撥號要看藍芽耳機及電話是否支援。

HFP定義了音訊閘道器(AG)和擴音元件(HF)兩個角色：
音訊閘道器(AG) – 該裝置為音訊（特別是手機）的輸入/輸出閘道器。
擴音元件(HF) – 該裝置作為音訊閘道器的遠端音訊輸入/輸出機制，並可提供若干遙控功能。

對於手機音訊的使用，首先連線的藍芽裝置需要支援hfp協議，並且需要與該裝置進行配對，如何進行藍芽配對這裡就不細說了，可以參照我的其他文章。主要分析下其連線過程。
對於系統自帶應用Settings中已配對的藍芽裝置介面(如下圖所示)，

public boolean onPreferenceChange(Preference preference, Object newValue) {
    if (preference == mDeviceNamePref) { //重新命名
        mCachedDevice.setName((String) newValue);
    } else if (preference instanceof CheckBoxPreference) {//check box
        LocalBluetoothProfile prof = getProfileOf(preference); ／/獲取對應的profile
        onProfileClicked(prof, (CheckBoxPreference) preference);
        return false;   // checkbox will update from onDeviceAttributesChanged() callback
    } else {
        return false;
    }
    return true;
}
 

接著看onProfileClicked()函式處理

private void onProfileClicked(LocalBluetoothProfile profile, CheckBoxPreference profilePref) {
    BluetoothDevice device = mCachedDevice.getDevice(); //獲取配對的藍芽裝置
    int status = profile.getConnectionStatus(device);  //獲取profile的連線狀態
    boolean isConnected =
            status == BluetoothProfile.STATE_CONNECTED;
    if (isConnected) { //如果是連線狀態則斷開連線
        askDisconnect(getActivity(), profile);
    } else { //沒有連線
        if (profile.isPreferred(device)) { //獲取profile是否是首選
            // profile is preferred but not connected: disable auto-connect
            profile.setPreferred(device, false); //設定對應profile的PRIORITY 為off，防止自動連線
            refreshProfilePreference(profilePref, profile); //重新整理check box狀態
        } else {
            profile.setPreferred(device, true); //設定對應profile的PRIORITY 為on
            mCachedDevice.connectProfile(profile); //連線指定profile
        }
    }
}
 

接著檢視CachedBluetoothDevice中的connectProfile函式連線某一profile。

void connectProfile(LocalBluetoothProfile profile) {
    mConnectAttempted = SystemClock.elapsedRealtime();
    // Reset the only-show-one-error-dialog tracking variable
    mIsConnectingErrorPossible = true;
    connectInt(profile); //連線profile
    refresh();    // 重新整理ui
}

synchronized void connectInt(LocalBluetoothProfile profile) {
    //檢視是否配對，如果沒有配對則進行配對，配對後進行連線，
    //如果配對則直接連線
    if (!ensurePaired()) { 
        return;
    }
    if (profile.connect(mDevice)) {//連線
        return;
    }
}

public boolean connect(BluetoothDevice device) {
    if (mService == null) return false;
    //獲取連線hfp的裝置
    List<BluetoothDevice> sinks = mService.getConnectedDevices();
    if (sinks != null) {
        for (BluetoothDevice sink : sinks) {
            mService.disconnect(sink); //斷開連線
        }
    } //連線hfp。
    return mService.connect(device);
}

public boolean connect(BluetoothDevice device) {
    HeadsetService service = getService();
    if (service == null) return false;
    return service.connect(device);
}

該方法中很明顯是去呼叫HeadsetService的connect方法。

public boolean connect(BluetoothDevice device) {
    enforceCallingOrSelfPermission(BLUETOOTH_ADMIN_PERM,
                                   "Need BLUETOOTH ADMIN permission");
    if (getPriority(device) == BluetoothProfile.PRIORITY_OFF) {
        return false;  //檢查priority
    }
    int connectionState = mStateMachine.getConnectionState(device);
    if (connectionState == BluetoothProfile.STATE_CONNECTED ||
        connectionState == BluetoothProfile.STATE_CONNECTING) {
        return false; //檢查連線狀態
    }
    mStateMachine.sendMessage(HeadsetStateMachine.CONNECT, device);
    return true;
}

BluetoothDevice device = (BluetoothDevice) message.obj;
//傳送廣播，正在連線hfp
broadcastConnectionState(device, BluetoothProfile.STATE_CONNECTING,
               BluetoothProfile.STATE_DISCONNECTED);
//連線遠端裝置。
if (!connectHfpNative(getByteAddress(device)) ) {
    //連線失敗，向外傳送連線失敗廣播
    broadcastConnectionState(device, BluetoothProfile.STATE_DISCONNECTED,
                   BluetoothProfile.STATE_CONNECTING);
    break;
}
synchronized (HeadsetStateMachine.this) {
    mTargetDevice = device;
    transitionTo(mPending); //切換到pending狀態
}
sendMessageDelayed(CONNECT_TIMEOUT, 30000);

static jboolean connectHfpNative(JNIEnv *env, jobject object, jbyteArray address) {
    jbyte *addr;
    bt_status_t status;
    if (!sBluetoothHfpInterface) return JNI_FALSE;
    addr = env->GetByteArrayElements(address, NULL);
    if (!addr) {
        jniThrowIOException(env, EINVAL);
        return JNI_FALSE;
    }
    if ((status = sBluetoothHfpInterface->connect((bt_bdaddr_t *)addr)) != BT_STATUS_SUCCESS) {
        ALOGE("Failed HF connection, status: %d", status);
    }
    env->ReleaseByteArrayElements(address, addr, 0);
    return (status == BT_STATUS_SUCCESS) ? JNI_TRUE : JNI_FALSE;
}

其中sBluetoothHfpInterface->connect會跳到藍芽協議棧進行連線，協議棧就先不進行分析了。

當協議棧連線狀態改變會回撥com_android_bluetooth_hfp.cpp中的方法connection_state_callback()。

static void connection_state_callback(bthf_connection_state_t state, bt_bdaddr_t* bd_addr) {
    jbyteArray addr;
    CHECK_CALLBACK_ENV
    addr = sCallbackEnv->NewByteArray(sizeof(bt_bdaddr_t));
    if (!addr) {
        checkAndClearExceptionFromCallback(sCallbackEnv, __FUNCTION__);
        return;
    }
    sCallbackEnv->SetByteArrayRegion(addr, 0, sizeof(bt_bdaddr_t), (jbyte*) bd_addr);
    sCallbackEnv->CallVoidMethod(mCallbacksObj, method_onConnectionStateChanged,
                                 (jint) state, addr);
    checkAndClearExceptionFromCallback(sCallbackEnv, __FUNCTION__);
    sCallbackEnv->DeleteLocalRef(addr);
}

private void onConnectionStateChanged(int state, byte[] address) {
    StackEvent event = new StackEvent(EVENT_TYPE_CONNECTION_STATE_CHANGED);
    event.valueInt = state;
    event.device = getDevice(address);
    sendMessage(STACK_EVENT, event);
}

//傳送廣播，連線成功
broadcastConnectionState(mTargetDevice, BluetoothProfile.STATE_CONNECTED,
                         BluetoothProfile.STATE_CONNECTING);
synchronized (HeadsetStateMachine.this) {
    mCurrentDevice = mTargetDevice; //mCurrentDevice表示已連線的裝置
    mTargetDevice = null; //mTargetDevice表示要連線的裝置
    transitionTo(mConnected); //切換到Connected狀態
}

private void broadcastConnectionState(BluetoothDevice device, int newState, int prevState) {
    /* Notifying the connection state change of the profile before sending the intent for
       connection state change, as it was causing a race condition, with the UI not being
       updated with the correct connection state. */
    mService.notifyProfileConnectionStateChanged(device, BluetoothProfile.HEADSET,newState, prevState);
    Intent intent = new Intent(BluetoothHeadset.ACTION_CONNECTION_STATE_CHANGED);
    intent.putExtra(BluetoothProfile.EXTRA_PREVIOUS_STATE, prevState);
    intent.putExtra(BluetoothProfile.EXTRA_STATE, newState);
    intent.putExtra(BluetoothDevice.EXTRA_DEVICE, device);
    mService.sendBroadcast(intent, HeadsetService.BLUETOOTH_PERM);
}

在mService.notifyProfileConnectionStateChanged中會將手機音訊的proirty設定為auto_connect，並且向外傳送BluetoothAdapter.ACTION_CONNECTION_STATE_CHANGED廣播。

在其他應用中可以通過廣播接收者註冊BluetoothHeadset.ACTION_CONNECTION_STATE_CHANGED該廣播，用來監聽hfp的連線狀態。

當手機音訊連線成功後，Settings應用中會更新ui介面。
LocalBluetoothProfileManager中會對所有的profile進行管理，其將hfp的profile新增到BluetoothEventManager中，BluetoothEventManager會註冊藍芽狀態改變、各profile狀態改變等廣播。
當BluetoothEventManager收到BluetoothHeadset.ACTION_CONNECTION_STATE_CHANGED廣播後，會根據action獲取對應的handler，呼叫對應handler的onReceive方法。
接收到該廣播跳到LocalBluetoothProfileManager內部類StateChangedHandler.onReceive->CachedBluetoothDevice.onProfileStateChanged ->refresh ->dispatchAttributesChanged
接著跳到DeviceProfilesSettings中的onDeviceAttributesChanged ->refresh.這裡會對介面進行更新，顯示其連線狀態資訊。

hfp連線過程已經分析完了，而斷開連線到過程和連線整體相差不多，就不再細說了。