最近GOOGLE发布了Android4.4，看了一下源码；4.4的蓝牙打开流程这一部分还是有些变化的，从界面上看蓝牙开关就是设置settings里那个switch开关，widget开关当然也可以，起点不同后续的流程是一样的。先来看systemServer.java的代码，蓝牙服务开启的地方，真机情况下我们关心的是最后一个else分支。

if (SystemProperties.get("ro.kernel.qemu").equals("1")) {
Slog.i(TAG, "No Bluetooh Service (emulator)");
} else if (factoryTest == SystemServer.FACTORY_TEST_LOW_LEVEL) {
Slog.i(TAG, "No Bluetooth Service (factory test)");
} else if (!context.getPackageManager().hasSystemFeature
(PackageManager.FEATURE_BLUETOOTH)) {
Slog.i(TAG, "No Bluetooth Service (Bluetooth Hardware Not Present)");
} else if (disableBluetooth) {
Slog.i(TAG, "Bluetooth Service disabled by config");
} else {
Slog.i(TAG, "Bluetooth Manager Service");
bluetooth = new BluetoothManagerService(context);
ServiceManager.addService(BluetoothAdapter.BLUETOOTH_MANAGER_SERVICE, bluetooth);
}


看下bluetoothManagerService的构造方法，我们看三个地方， loadStoredNameAndAddress()是读取蓝牙打开默认名称的地方，isBluetoothPersistedStateOn()是判断是否已打开蓝牙的，如果已打开，后续操作要执行开启蓝牙的动作

BluetoothManagerService(Context context) {
mHandler = new BluetoothHandler(IoThread.get().getLooper());

mContext = context;
mBluetooth = null;
mQBluetooth = null;
mBinding = false;
mUnbinding = false;
mEnable = false;
mState = BluetoothAdapter.STATE_OFF;
mQuietEnableExternal = false;
mEnableExternal = false;
mAddress = null;
mName = null;
mErrorRecoveryRetryCounter = 0;
mContentResolver = context.getContentResolver();
mCallbacks = new RemoteCallbackList();
mQCallbacks = new RemoteCallbackList();
mStateChangeCallbacks = new RemoteCallbackList();
IntentFilter filter = new IntentFilter(Intent.ACTION_BOOT_COMPLETED);
filter.addAction(BluetoothAdapter.ACTION_LOCAL_NAME_CHANGED);
filter.addAction(Intent.ACTION_USER_SWITCHED);
registerForAirplaneMode(filter);
mContext.registerReceiver(mReceiver, filter);
loadStoredNameAndAddress();
if (isBluetoothPersistedStateOn()) {
mEnableExternal = true;
}
}


另外的registerForAirplaneMode方法，如下

private void registerForAirplaneMode(IntentFilter filter) {
final ContentResolver resolver = mContext.getContentResolver();
final String airplaneModeRadios = Settings.Global.getString(resolver,
Settings.Global.AIRPLANE_MODE_RADIOS);
final String toggleableRadios = Settings.Global.getString(resolver,
Settings.Global.AIRPLANE_MODE_TOGGLEABLE_RADIOS);
boolean mIsAirplaneSensitive = airplaneModeRadios == null ? true :
airplaneModeRadios.contains(Settings.Global.RADIO_BLUETOOTH);
if (mIsAirplaneSensitive) {
filter.addAction(Intent.ACTION_AIRPLANE_MODE_CHANGED);
}
}

其中

Settings.Global.getString(resolver,
Settings.Global.AIRPLANE_MODE_TOGGLEABLE_RADIOS)



获取到的值是在String文件中定义的，如：


cell,bluetooth,wifi,nfc,wimax


表示如果开启飞行模式下，哪些服务将会被关闭。所以registerForAirplaneMode方法就是在如果蓝牙也受飞行模式影响，那么飞行模式的变化也将使蓝牙服务收到相应广播。

界面上开关就是BluetoothEnabler.java这个类了，而setBluetoothEnabled()则是具体开关动作。其中有开关的回调函数，代码如下：

public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// Show toast message if Bluetooth is not allowed in airplane mode
if (isChecked
&& (WifiSettings.needPrompt(mContext) || !WirelessSettings.isRadioAllowed(
mContext, Settings.Global.RADIO_BLUETOOTH))) {
Toast.makeText(mContext, R.string.wifi_in_airplane_mode,
Toast.LENGTH_SHORT).show();
// Reset switch to off
buttonView.setChecked(false);
}

// shouldn‘t setBluetoothEnabled(true) in airplane mode.
if (mLocalAdapter != null) {
if (isChecked && WifiSettings.needPrompt(mContext)) {
return;
}
mLocalAdapter.setBluetoothEnabled(isChecked);
}
mSwitch.setEnabled(false);
}

Android4.4 蓝牙源码部分分析