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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 valueif (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 LocatorStartLocator();} 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。