先WiFi，后 定位，再从蓝牙到NFC，这个就是我大致熟悉开源鸿蒙代码的一个顺序流程，WiFi 的年前差不多基本流程熟悉了，当然还有很多细节和内容没有写到，后续都会慢慢的丰富起来，这一篇将开启GNSS的篇章，先从GNSS使能开始，代码还是选取开源鸿蒙HarmonyOS 4.0的代码基线。
界面部分代码省略，直接JS看调用哪个接口，往下梳理
代码位置：base/location/frameworks/native/source/locator.cpp —> locator.cpp 的实现是 LocatorImpl

void LocatorImpl::EnableAbility(bool enable)
{
    if (!Init()) {
        return;
    }
    sptr<LocatorProxy> proxy = GetProxy();
    if (proxy == nullptr) {
        LBSLOGE(LOCATOR_STANDARD, "%{public}s get proxy failed.", __func__);
        return;
    }
    LocationErrCode errCode = proxy->EnableAbilityV9(enable);       ---> 使能，继续看这个
    // cache the value
    if (errCode == ERRCODE_SUCCESS) {               ---> 使能成功，保存现在的状态
        if (locationDataManager_ != nullptr) {
            locationDataManager_->SetCachedSwitchState(enable ? ENABLED : DISABLED);
        }
    }
}

// base/location/frameworks/native/source/locator_proxy.cpp
void LocatorProxy::EnableAbility(bool isEnabled)
{
    MessageParcel data;
    MessageParcel reply;
    if (!data.WriteInterfaceToken(GetDescriptor())) {
        return;
    }
    data.WriteBool(isEnabled);
    int error = SendMsgWithDataReply(static_cast<int>(LocatorInterfaceCode::ENABLE_ABILITY), data, reply);
    LBSLOGD(LOCATOR_STANDARD, "Proxy::EnableAbility Transact ErrCodes = %{public}d", error);
}
//处理这个消息 ENABLE_ABILITY
// base/location/services/location_locator/locator/source/locator_skeleton.cpp
int LocatorAbilityStub::PreEnableAbility(MessageParcel &data, MessageParcel &reply, AppIdentity &identity)
{
    if (!CommonUtils::CheckSystemPermission(identity.GetTokenId(), identity.GetTokenIdEx())) {
        LBSLOGE(LOCATOR, "CheckSystemPermission return false, [%{public}s]",
            identity.ToString().c_str());
        reply.WriteInt32(ERRCODE_SYSTEM_PERMISSION_DENIED);
        return ERRCODE_SYSTEM_PERMISSION_DENIED;
    }
    if (!CheckSettingsPermission(reply, identity)) {
        return ERRCODE_PERMISSION_DENIED;
    }
    auto locatorAbility = DelayedSingleton<LocatorAbility>::GetInstance();
    if (locatorAbility == nullptr) {
        LBSLOGE(LOCATOR, "PreEnableAbility: LocatorAbility is nullptr.");
        reply.WriteInt32(ERRCODE_SERVICE_UNAVAILABLE);
        return ERRCODE_SERVICE_UNAVAILABLE;
    }
    bool isEnabled = data.ReadBool();
    // 上面主要是权限的check，这里我们看下面这句
    reply.WriteInt32(locatorAbility->EnableAbility(isEnabled)); 
    return ERRCODE_SUCCESS;
}

// base/location/services/location_locator/locator/source/locator_ability.cpp
LocationErrCode LocatorAbility::EnableAbility(bool isEnabled)
{
    LBSLOGI(LOCATOR, "EnableAbility %{public}d", isEnabled);
    int modeValue = isEnabled ? 1 : 0;
    if (modeValue == QuerySwitchState()) {
        LBSLOGD(LOCATOR, "no need to set location ability, enable:%{public}d", modeValue);
        return ERRCODE_SUCCESS;
    }
    // 更新 value 值
    Uri locationDataEnableUri(LOCATION_DATA_URI);
    LocationErrCode errCode = DelayedSingleton<LocationDataRdbHelper>::GetInstance()->
        SetValue(locationDataEnableUri, LOCATION_DATA_COLUMN_ENABLE, modeValue);
    if (errCode != ERRCODE_SUCCESS) {
        LBSLOGE(LOCATOR, "%{public}s: can not set state to db", __func__);
        return ERRCODE_SERVICE_UNAVAILABLE;
    }
    UpdateSaAbility();   ---> 主要看下这个方法
    std::string state = isEnabled ? "enable" : "disable";
    WriteLocationSwitchStateEvent(state);
    return ERRCODE_SUCCESS;
}

继续看 UpdateSaAbility 方法干个啥。

LocationErrCode LocatorAbility::UpdateSaAbility()
{
    auto event = AppExecFwk::InnerEvent::Get(EVENT_UPDATE_SA, 0);
    if (locatorHandler_ != nullptr) {
        locatorHandler_->SendHighPriorityEvent(event);    ---> 发送EVENT_UPDATE_SA 事件
    }
    return ERRCODE_SUCCESS;
}

// 处理 EVENT_UPDATE_SA 这个事件的地方：
void LocatorHandler::ProcessEvent(const AppExecFwk::InnerEvent::Pointer& event)
{
	……… ………… ………
    LBSLOGI(LOCATOR, "ProcessEvent event:%{public}d", eventId);
    switch (eventId) {
        case EVENT_UPDATE_SA: {
            if (locatorAbility != nullptr) {
                locatorAbility->UpdateSaAbilityHandler();    ---> 看这个方法
            }
            break;
	……… ………… ………
}

void LocatorAbility::UpdateSaAbilityHandler()
{
    int state = QuerySwitchState();
    LBSLOGI(LOCATOR, "update location subability enable state, switch state=%{public}d, action registered=%{public}d",
        state, isActionRegistered);
    auto locatorBackgroundProxy = DelayedSingleton<LocatorBackgroundProxy>::GetInstance();
    if (locatorBackgroundProxy == nullptr) {
        LBSLOGE(LOCATOR, "UpdateSaAbilityHandler: LocatorBackgroundProxy is nullptr");
        return;
    }
    locatorBackgroundProxy.get()->OnSaStateChange(state == ENABLED);
}

// base/location/services/location_locator/locator/source/locator_background_proxy.cpp
void LocatorBackgroundProxy::OnSaStateChange(bool enable)
{
    if (proxySwtich_ == enable || !featureSwitch_) {
        return;
    }
    LBSLOGD(LOCATOR_BACKGROUND_PROXY, "OnSaStateChange %{public}d", enable);
    proxySwtich_ = enable;
    if (enable && !requestsList_->empty()) {    ---> 位置打开，如果没有请求就不会Start Locator
        StartLocator();
    } else {
        StopLocator();
    }
}

开源鸿蒙打开location开关使能比较简单，主要是状态上的处理和更新，下一篇章继续记录发起定位的流程。