轉(zhuǎn)載請(qǐng)注明出處：http://blog.csdn.net/vnanyesheshou/article/details/71811288

上一篇說了下A2DP的一些基本操作星立，這篇分析下系統(tǒng)應(yīng)用取试、系統(tǒng)源碼是如何操作A2DP的贾铝。尤其是其連接過程，基于Android4.3源碼均唉。Andorid手機(jī)一般都是做為A2DP Audio Source端。

1 連接過程

媒體音頻也就是A2DP，首先連接的藍(lán)牙設(shè)備需要支持A2DP協(xié)議（并且做為A2DP Audio Sink端）辱挥，并且需要與該設(shè)備進(jìn)行配對(duì)，如何進(jìn)行藍(lán)牙配對(duì)這里就不細(xì)說了边涕，可以參照我的其他文章晤碘。主要分析下其連接過程褂微。
對(duì)于系統(tǒng)自帶應(yīng)用Settings中已配對(duì)的藍(lán)牙設(shè)備界面(如下圖所示)：

這里寫圖片描述

其對(duì)應(yīng)文件路徑：
packages/apps/Settings/src/com/android/settings/bluetooth/DeviceProfilesSettings.Java
點(diǎn)擊媒體音頻進(jìn)行連接，調(diào)用onPreferenceChange哼蛆。

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

接著看onProfileClicked()函數(shù)處理

private void onProfileClicked(LocalBluetoothProfile profile, CheckBoxPreference profilePref) {
    BluetoothDevice device = mCachedDevice.getDevice(); //獲取配對(duì)的藍(lán)牙設(shè)備
    int status = profile.getConnectionStatus(device);  //獲取profile的連接狀態(tài)
    boolean isConnected =
            status == BluetoothProfile.STATE_CONNECTED;
    if (isConnected) { //如果是連接狀態(tài)則斷開連接
        askDisconnect(getActivity(), profile);
    } else { //沒有連接
        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(shè)置對(duì)應(yīng)profile的PRIORITY 為off蕊梧，防止自動(dòng)連接
            refreshProfilePreference(profilePref, profile); //刷新check box狀態(tài)
        } else {
            profile.setPreferred(device, true); //設(shè)置對(duì)應(yīng)profile的PRIORITY 為on
            mCachedDevice.connectProfile(profile); //連接指定profile
        }
    }
}

接著查看CachedBluetoothDevice中的connectProfile函數(shù)連接某一profile。

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

synchronized void connectInt(LocalBluetoothProfile profile) {
    //查看是否配對(duì)腮介，如果沒有配對(duì)則進(jìn)行配對(duì)肥矢，配對(duì)后進(jìn)行連接，
    //如果配對(duì)則直接連接
    if (!ensurePaired()) { 
        return;
    }
    if (profile.connect(mDevice)) {//連接
        return;
    }
}

connectProfile() ——>connectInt()
connectInt()函數(shù)中會(huì)先判斷是否配對(duì)叠洗，如果沒有配對(duì)則開始配對(duì)甘改，配對(duì)成功后連接profile。
如果已經(jīng)配對(duì)則直接連接profile灭抑。
對(duì)于profile.connect(mDevice)會(huì)根據(jù)profile調(diào)用各自對(duì)應(yīng)的connect方法十艾。（如手機(jī)音頻則對(duì)應(yīng)HeadsetProfile，媒體音頻對(duì)應(yīng)A2dpProfile）腾节。這里查看手機(jī)音頻的連接A2dpProfile忘嫉。

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

A2dpProfile.java中的connect()方法案腺，mService是通過getProfileProxy獲取的BluetoothA2DP代理對(duì)象庆冕，通過其進(jìn)行A2DP相關(guān)操作。
mService.connect跳到Bluetooth應(yīng)用中劈榨，
代碼路徑：packages/apps/Bluetooth/src/com/android/bluetooth/a2dp/A2dpService.java
先調(diào)用到內(nèi)部類BluetoothA2dpBinder的connect方法访递。

public boolean connect(BluetoothDevice device) {
    A2dpService service = getService();
    if (service == null) return false;
    return service.connect(device);
}

該方法中很明顯是去調(diào)用A2dpService的connect方法。接著看A2dpService中的connect

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; //檢查連接狀態(tài)
    }

    mStateMachine.sendMessage(A2dpStateMachine.CONNECT, device);
    return true;
}

A2dpService的connect()函數(shù)會(huì)對(duì)priority和連接狀態(tài)進(jìn)行必要的檢查同辣，不符合條件則返回false拷姿。符合條件則向狀態(tài)機(jī)發(fā)送消息A2dpStateMachine.CONNECT。
此時(shí)A2dpStateMachine中狀態(tài)應(yīng)該是Disconnected旱函，所以查看Disconnected state中的處理

BluetoothDevice device = (BluetoothDevice) message.obj;
//發(fā)送廣播响巢，正在連接A2DP
broadcastConnectionState(device, BluetoothProfile.STATE_CONNECTING,
               BluetoothProfile.STATE_DISCONNECTED);
//連接遠(yuǎn)端設(shè)備。
if (!connectA2dpNative(getByteAddress(device)) ) {
    //連接失敗陡舅，向外發(fā)送連接失敗廣播
    broadcastConnectionState(device, BluetoothProfile.STATE_DISCONNECTED,
                   BluetoothProfile.STATE_CONNECTING);
    break;
}

synchronized (A2dpStateMachine.this) {
    mTargetDevice = device; //mTargetDevice要連接的設(shè)備
    transitionTo(mPending); //切換到pending狀態(tài)
} //超時(shí)處理
sendMessageDelayed(CONNECT_TIMEOUT, 30000);

A2DPStateMachine調(diào)用connectA2dpNative()函數(shù)來進(jìn)行媒體音頻的連接抵乓。connectA2dpNative是native方法，跳轉(zhuǎn)到com_android_bluetooth_a2dp.cpp中靶衍，調(diào)用對(duì)應(yīng)的方法connectA2dpNative

static jboolean connectA2dpNative(JNIEnv *env, jobject object, jbyteArray address) {
    jbyte *addr;
    bt_bdaddr_t * btAddr;
    bt_status_t status;
    if (!sBluetoothA2dpInterface) return JNI_FALSE;

    addr = env->GetByteArrayElements(address, NULL);
    btAddr = (bt_bdaddr_t *) addr;
    if (!addr) {
        jniThrowIOException(env, EINVAL);
        return JNI_FALSE;
    }

    if ((status = sBluetoothA2dpInterface->connect((bt_bdaddr_t *)addr)) != BT_STATUS_SUCCESS) {
    }
    env->ReleaseByteArrayElements(address, addr, 0);
    return (status == BT_STATUS_SUCCESS) ? JNI_TRUE : JNI_FALSE;
}

其中sBluetoothA2dpInterface->connect會(huì)跳到hardware灾炭、藍(lán)牙協(xié)議棧進(jìn)行連接，這就先不進(jìn)行分析了颅眶。

2 狀態(tài)回調(diào)##

當(dāng)協(xié)議棧連接狀態(tài)改變會(huì)回調(diào)com_android_bluetooth_a2dp.cpp中的方法bta2dp_connection_state_callback蜈出。

static void bta2dp_connection_state_callback(btav_connection_state_t state, bt_bdaddr_t* bd_addr) {
    jbyteArray addr;
    if (!checkCallbackThread()) {                                       \
        return;                                                         \
    }
    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);
}

bta2dp_connection_state_callback方法中會(huì)從cpp層調(diào)用到j(luò)ava層，對(duì)應(yīng)于A2DPStateMachine中的onConnectionStateChanged函數(shù)

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);
}

onConnectionStateChanged函數(shù)中發(fā)送消息STACK_EVENT（攜帶狀態(tài)和藍(lán)牙地址）涛酗，此時(shí)是Pending state铡原，收到該消息調(diào)用processConnectionEvent偷厦。
正常連接成功應(yīng)該會(huì)先收到CONNECTION_STATE_CONNECTING狀態(tài)，然后收到CONNECTION_STATE_CONNECTED狀態(tài)燕刻。

//發(fā)送廣播只泼，連接成功
broadcastConnectionState(mTargetDevice, BluetoothProfile.STATE_CONNECTED,
                         BluetoothProfile.STATE_CONNECTING);
synchronized (A2dpStateMachine.this) {
    mCurrentDevice = mTargetDevice;//mCurrentDevice表示已連接的設(shè)備
    mTargetDevice = null; //mTargetDevice表示要連接的設(shè)備
    transitionTo(mConnected);//切換到Connected狀態(tài)
}

收到CONNECTION_STATE_CONNECTED狀態(tài)，后向外發(fā)送連接成功的廣播卵洗，狀態(tài)機(jī)切換到Connected狀態(tài)请唱。

private void broadcastConnectionState(BluetoothDevice device, int newState, int prevState) {
    //AudioManager設(shè)置A2DP的連接狀態(tài)
    int delay = mAudioManager.setBluetoothA2dpDeviceConnectionState(device, newState);
    mWakeLock.acquire();
    //延時(shí)處理，發(fā)送廣播 
    mIntentBroadcastHandler.sendMessageDelayed(mIntentBroadcastHandler.
        obtainMessage(MSG_CONNECTION_STATE_CHANGED,
           prevState,newState,device),
           delay);
}

broadcastConnectionState中會(huì)向AudioManager中設(shè)置A2DP的連接狀態(tài)过蹂，返回值用來延時(shí)發(fā)送廣播十绑。AudioManager設(shè)置A2DP的連接狀態(tài)非常重要，這樣音頻系統(tǒng)根據(jù)當(dāng)前狀態(tài)酷勺，判斷音頻從哪里發(fā)出（藍(lán)牙a2dp本橙、揚(yáng)聲器、耳機(jī)）脆诉。

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