HIDL
Vhal启动流程
首先查看VehicleService的main方法：
int main(int /* argc */, char* /* argv */ []) {
//加载VehiclePropertyStore
auto store = std::make_unique<VehiclePropertyStore>();
//加载VehicleConnector
auto connector = std::make_unique<XXXVehicleConnector>();
//加载VehicleHal
auto hal = std::make_unique<XXXVehicleHal>(store.get(), connector.get());
//加载VehicalHalManager
auto service = std::make_unique<VehicleHalManager>(hal.get());
connector->setValuePool(hal->getValuePool());
android::hardware::configureRpcThreadpool(4, true /* callerWillJoin */);
...
android::status_t status = service->registerAsService();
...
}
，主要创建了四个类型的对象，分别是VehiclePropertyStore、VehicleConnector、VehicleHal和vehicleHalManager，首先
VehicleService会创建未初始化的VehiclePropertyStore和VehicleConnector，然后通过这两个对象创建VehicleHal。
创建VehicleHal
查看VehicleHal的构造函数：
XXXVehicleHal::XXXVehicleHal(VehiclePropertyStore *propStore, XXXVehicleConnector *connector)
: mPropStore(propStore),
mConnector(connector)
{
initStaticConfig();
for (size_t i = 0; i < arraysize(kVehicleProperties); i++)
{
mPropStore->registerProperty(kVehicleProperties[i].config);
}
mVehicleClient->registerPropertyValueCallback(std::bind(&EmulatedVehicleHal::onPropertyValue,
this, std::placeholders::_1,
std::placeholders::_2));
}
，主要执行了initStaicConfig方法，并向VehiclePropertyStore中写入config
默认VehiclePropConfig的加载
查看initStaticConfig的代码：
void EmulatedVehicleHal::initStaticConfig() {
for (auto&& it = std::begin(kVehicleProperties); it != std::end(kVehicleProperties); ++it) {
const auto& cfg = it->config;
VehiclePropertyStore::TokenFunction tokenFunction = nullptr;
switch (cfg.prop) {
case OBD_FREEZE_FRAME: {
tokenFunction = [](const VehiclePropValue& propValue) {
return propValue.timestamp;
};
break;
}
default:
break;
}
mPropStore->registerProperty(cfg, tokenFunction);
}
}
，该方法从kVehicleProperties中读取property的配置信息，向VehiclePropertyStore中注册配置信息。同样，在VehicleHal的构造函数中，也执行了操作：
for (size_t i = 0; i < arraysize(kVehicleProperties); i++)
{
mPropStore->registerProperty(kVehicleProperties[i].config);
}
在DefaultConfig.h中查看kVehicleProperties的定义：
const ConfigDeclaration kVehicleProperties[]{
{.config =
{
.prop = toInt(VehicleProperty::INFO_FUEL_CAPACITY),
.access = VehiclePropertyAccess::READ,
.changeMode = VehiclePropertyChangeMode::STATIC,
},
.initialValue = {.floatValues = {15000.0f}}},
...
};
，是ConfigDeclaration类型的数组，ConfigDeclaration的定义在DefaultConfig.h中：
struct ConfigDeclaration {
VehiclePropConfig config;
VehiclePropValue::RawValue initialValue;
std::map<int32_t, VehiclePropValue::RawValue> initialAreaValues;
};
，包含了VehiclePropConfig、property的初始物理值和在每个area的对应初始值。
VehiclePropConfig的定义详见Vhal 结构 与 get/set 流程：
查看VehiclePropertyStore的registerProperty方法：
void VehiclePropertyStore::registerProperty(const VehiclePropConfig& config,
VehiclePropertyStore::TokenFunction tokenFunc) {
MuxGuard g(mLock);
mConfigs.insert({ config.prop, RecordConfig { config, tokenFunc } });
}
，向mConfigs中插入了一个prop和RecordConfig的键值对，其中mConfigs是一个property id到RecordConfig的map：
struct RecordConfig {
VehiclePropConfig propConfig;
TokenFunction tokenFunction;
};
std::unordered_map<int32_t /* VehicleProperty */, RecordConfig> mConfigs;
启动VehicleHalManager
在完成VehicleHal的创建后，会进行VehicleHalManager的启动，这一步会创建VehicleHalManager，并对之前创建的一些对象进行初始化的操作。
首先查看VehicleHalManager的构造函数：
VehicleHalManager(VehicleHal* vehicleHal)
: mHal(vehicleHal),
//首先创建`SubscriptionManager`对象
mSubscriptionManager(std::bind(&VehicleHalManager::onAllClientsUnsubscribed,
this, std::placeholders::_1)) {
//然后执行初始化方法
init();
}
，这一步会先创建SubscriptionManager的对象用于管理subscribe/unsubscribe，然后执行初始化的操作。
创建SubscriptionManager
这一步主要是将SubscriptionManager的mOnPropertyUnsubscribed方法设置为VehicleHalManager的onAllClientsUnsubscribed方法，并设置mCallbackDeathRecipient的 为onCallbackDead方法：
SubscriptionManager(const OnPropertyUnsubscribed& onPropertyUnsubscribed)
: mOnPropertyUnsubscribed(onPropertyUnsubscribed),
mCallbackDeathRecipient(new DeathRecipient(
std::bind(&SubscriptionManager::onCallbackDead, this, std::placeholders::_1)))
{}
onAllClientUnsubscribed方法主要执行了VehicleHal的unsubscribe方法：
void VehicleHalManager::onAllClientsUnsubscribed(int32_t propertyId) {
mHal->unsubscribe(propertyId);
}
方法onCallBackDead在订阅属性的远程对象的binder死亡时，取消该远程对象对属性的订阅：
void SubscriptionManager::onCallbackDead(uint64_t cookie) {
...
ClientId clientId = cookie;
std::vector<int32_t> props;
{
MuxGuard g(mLock);
//获取id对应的client对象
const auto& it = mClients.find(clientId);
if (it == mClients.end()) {
return;
}
const auto& halClient = it->second;
//获取订阅的属性
props = halClient->getSubscribedProperties();
}
//取消订阅
for (int32_t propId : props) {
unsubscribe(clientId, propId);
}
}
初始化VehicleHalManager
在前面的步骤中，完成了所有对象的创建，在这一步，需要完成对创建的对象的初始化操作。
查看VehicleHalManager::init方法：
void VehicleHalManager::init() {
...
//初始化VehicleHal
mHal->init(&mValueObjectPool,
std::bind(&VehicleHalManager::onHalEvent, this, _1),
std::bind(&VehicleHalManager::onHalPropertySetError, this,
_1, _2, _3));
...
}
执行VehicleHal的init方法。
初始化VehicleHal
VehicleHal的init方法在VehicleHal.h中：
void init(
VehiclePropValuePool* valueObjectPool,
const HalEventFunction& onHalEvent,
const HalErrorFunction& onHalError) {
mValuePool = valueObjectPool;
mOnHalEvent = onHalEvent;
mOnHalPropertySetError = onHalError;
onCreate();
}
，在这一步里，设置VehicleHal的mValuePool、mOnHalEvent和mOnHalPropertySetError为VehicleHalManager的mValueObjectPool、onHalEvent和onHalPorpertySetError，第一个对象用来进行property对象的复用，第二个和第三个则是设置了两个回调函数。 进行了上述设置后，执行onCreate方法：
void EmulatedVehicleHal::onCreate() {
static constexpr bool shouldUpdateStatus = true;
for (auto& it : kVehicleProperties) {
VehiclePropConfig cfg = it.config;
int32_t numAreas = cfg.areaConfigs.size();
...
for (int i = 0; i < numAreas; i++) {
...
VehiclePropValue prop = {
.areaId = curArea,
.prop = cfg.prop,
};
...
mPropStore->writeValue(prop, shouldUpdateStatus);
}
}
...
}
，在onCreate方法中，会从kVehicleProperties中读取所有的config，并根据其中的area执行VehiclePropertyStore::writeValue方法，这一步会将在kVehicleProperties中设定的属性值写入到VehiclePropertyStore中。
AIDL
Vhal启动流程
首先查看VehicleService中定义的main方法：
int main(int /* argc */, char* /* argv */[]) {
...
if (!ABinderProcess_setThreadPoolMaxThreadCount(4)) {
...
}
ABinderProcess_startThreadPool();
//创建VehicleHardWare对象
std::unique_ptr<XXXVehicleHardware> hardware = std::make_unique<XXXVehicleHardware>();
//创建VehicleHal对象
std::shared_ptr<XXXVehicleHal> vhal =
::ndk::SharedRefBase::make<XXXVehicleHal>(std::move(hardware));
...
binder_exception_t err = AServiceManager_addService(
vhal->asBinder().get(), "android.hardware.automotive.vehicle.IVehicle/default");
...
ABinderProcess_joinThreadPool();
...
return 0;
}
创建并初始化VehicleHardware
XXXVehicleHardware::XXXVehicleHardware()
: XXXVehicleHardware(DEFAULT_CONFIG_DIR, OVERRIDE_CONFIG_DIR, false) {}
XXXVehicleHardware::XXXVehicleHardware(std::string defaultConfigDir,
std::string overrideConfigDir, bool forceOverride)
: mValuePool(std::make_unique<VehiclePropValuePool>()),
mServerSidePropStore(new VehiclePropertyStore(mValuePool)),
...
mRecurrentTimer(new RecurrentTimer()),
...
mDefaultConfigDir(defaultConfigDir),
mOverrideConfigDir(overrideConfigDir),
mForceOverride(forceOverride) {
init();
}
，这一步首先创建了一个VehiclePropValuePool，然后创建一个VehiclePropertyStore，然后，设置了mDefaultConfigDir和mOverrideConfigDir，后续执行了init方法：
void XXXVehicleHardware::init() {
//首先加载配置信息
for (auto& [_, configDeclaration] : loadConfigDeclarations()) {
VehiclePropConfig cfg = configDeclaration.config;
VehiclePropertyStore::TokenFunction tokenFunction = nullptr;
...
//将配置信息注册到`VehiclePropertyStore`中
mServerSidePropStore->registerProperty(cfg, tokenFunction);
...
//将config中的初始值写入
storePropInitialValue(configDeclaration);
}
...
//设置VehiclePropertyStore在property值改变时的回调函数为XXXVehicleHardware::onValueChangeCallback
mServerSidePropStore->setOnValueChangeCallback(
[this](const VehiclePropValue& value) { return onValueChangeCallback(value); });
}
加载默认配置并设置VehiclePropertyStore
查看loadConfigDeclarations方法：
std::unordered_map<int32_t, ConfigDeclaration> XXXVehicleHardware::loadConfigDeclarations() {
std::unordered_map<int32_t, ConfigDeclaration> configsByPropId;
loadPropConfigsFromDir(mDefaultConfigDir, &configsByPropId);
if (mForceOverride ||
android::base::GetBoolProperty(OVERRIDE_PROPERTY, /*default_value=*/false)) {
loadPropConfigsFromDir(mOverrideConfigDir, &configsByPropId);
}
return configsByPropId;
}
，主要调用了loadPropConfigsFromDir方法：
void XXXVehicleHardware::loadPropConfigsFromDir(
const std::string& dirPath,
std::unordered_map<int32_t, ConfigDeclaration>* configsByPropId) {
...
if (auto dir = opendir(dirPath.c_str()); dir != NULL) {
std::regex regJson(".*[.]json", std::regex::icase);
while (auto f = readdir(dir)) {
...
auto result = mLoader.loadPropConfig(filePath);
...
for (auto& [propId, configDeclaration] : result.value()) {
(*configsByPropId)[propId] = std::move(configDeclaration);
}
}
closedir(dir);
}
}
，这一步主要通过mLoader从json文件中加载配置信息，mLoader是JsonConfigLoader类的实例，查看其loadPropConfig方法：
android::base::Result<std::unordered_map<int32_t, ConfigDeclaration>>
JsonConfigLoader::loadPropConfig(std::istream& is) {
return mParser->parseJsonConfig(is);
}
android::base::Result<std::unordered_map<int32_t, ConfigDeclaration>>
JsonConfigLoader::loadPropConfig(const std::string& configPath) {
std::ifstream ifs(configPath.c_str());
...
return loadPropConfig(ifs);
}
，调用了parseJsonConfig方法从json文件中解析配置信息，json文件的格式如下：
{
"apiVersion": 1,
"properties": [
{
// property id
"property": "VehicleProperty::INFO_FUEL_CAPACITY",
// (optional, number/string) property 访问模式
"access": "VehiclePropertyAccess::READ",
// (optional, number/string) propert change mode
"changeMode": "VehiclePropertyChangeMode::STATIC",
// (optional, string) config string.
"configString": "blahblah",
// (optional, array of number/string) config array.
"configArray": [1, 2, "Constants::HVAC_ALL"],
// (optional, object) property 的默认值
"defaultValue": {
// (optional, array of int number/string) Int values.
"int32Values": [1, 2, "Constants::HVAC_ALL"],
// (optional, array of int number/string) Long values.
"int64Values": [1, 2],
// (optional, array of float number/string) Float values.
"floatValues": [1.1, 2.2],
// (optional, string) String value.
"stringValue": "test"
},
"minSampleRate": 1,
"maxSampleRate": 10,
// (optional, array of objects) 不同area的配置
"areas:" [
{
"areaId": "Constants::DOOR_1_LEFT",
// (optional number/string)
"minInt32Value": 1,
// (optional number/string)
"maxInt32Value": 10,
// (optional number/string)
"minInt64Value": 1,
// (optional number/string)
"maxInt64Value": 10,
// (optional number/string)
"minFloatValue": 1,
// (optional number/string)
"maxFloatValue": 10,
// (optional object)
"defaultValue": {
"int32Values": [1, 2, "Constants::HVAC_ALL"],
"int64Values": [1, 2],
"floatValues": [1.1, 2.2],
"stringValue": "test"
}
}
]
}
]
}
在执行完loadConfigDeclarations后，调用VehiclePropertyStore::registerProperty方法，该步与HIDL相同。然后，执行storePropInitialValue方法：
void FakeVehicleHardware::storePropInitialValue(const ConfigDeclaration& config) {
const VehiclePropConfig& vehiclePropConfig = config.config;
int propId = vehiclePropConfig.prop;
bool globalProp = isGlobalProp(propId);
size_t numAreas = globalProp ? 1 : vehiclePropConfig.areaConfigs.size();
for (size_t i = 0; i < numAreas; i++) {
int32_t curArea = globalProp ? 0 : vehiclePropConfig.areaConfigs[i].areaId;
VehiclePropValue prop = {
.areaId = curArea,
.prop = propId,
.timestamp = elapsedRealtimeNano(),
};
...
auto result =
mServerSidePropStore->writeValue(mValuePool->obtain(prop), /*updateStatus=*/true);
...
}
}
，这一步也与HIDL实现类似，向VehicleProeprtyStore中写入了config中配置的初始值。
创建VehicleHal
XXXVehicleHal::XXXVehicleHal(std::unique_ptr<IVehicleHardware> vehicleHardware)
: mVehicleHardware(std::move(vehicleHardware)),
mPendingRequestPool(std::make_shared<PendingRequestPool>(TIMEOUT_IN_NANO)) {
...
IVehicleHardware* vehicleHardwarePtr = mVehicleHardware.get();
//创建SubscriptionManager
mSubscriptionManager = std::make_shared<SubscriptionManager>(vehicleHardwarePtr);
//绑定回调函数
std::weak_ptr<SubscriptionManager> subscriptionManagerCopy = mSubscriptionManager;
mVehicleHardware->registerOnPropertyChangeEvent(
std::make_unique<IVehicleHardware::PropertyChangeCallback>(
[subscriptionManagerCopy](std::vector<VehiclePropValue> updatedValues) {
onPropertyChangeEvent(subscriptionManagerCopy, updatedValues);
}));
mVehicleHardware->registerOnPropertySetErrorEvent(
std::make_unique<IVehicleHardware::PropertySetErrorCallback>(
[subscriptionManagerCopy](std::vector<SetValueErrorEvent> errorEvents) {
onPropertySetErrorEvent(subscriptionManagerCopy, errorEvents);
}));
...
}
，在该步中，首先创建了SubscriptionManager，然后将onPropertyChangeEvent和onPropertySetErrorEvent方法注册到VehicleHardware上。
属性配置的加载
在AIDL实现中，将属性的初始配置加载从读取DefaultConfig.h头文件转移到了读取XXXpackages.json文件。
JsonConfigLoader加载json文件
查看JsonConfigParser的parseJsonConfig方法：
Result<std::unordered_map<int32_t, ConfigDeclaration>> JsonConfigParser::parseJsonConfig(
std::istream& is) {
...
std::unordered_map<int32_t, ConfigDeclaration> configsByPropId;
...
Json::Value properties = root["properties"];
...
for (unsigned int i = 0; i < properties.size(); i++) {
if (auto maybeConfig = parseEachProperty(properties[i], &errors); maybeConfig.has_value()) {
configsByPropId[maybeConfig.value().config.prop] = std::move(maybeConfig.value());
}
}
...
return configsByPropId;
}
，查看parseEachProperty方法：
std::optional<ConfigDeclaration> JsonConfigParser::parseEachProperty(
const Json::Value& propJsonValue, std::vector<std::string>* errors) {
...
int32_t propId;
if (!tryParseJsonValueToVariable(propJsonValue, "property", /*optional=*/false, &propId,
errors)) {
return std::nullopt;
}
configDecl.config.prop = propId;
std::string propStr = propJsonValue["property"].toStyledString();
//解析access
parseAccessChangeMode(propJsonValue, "access", propId, propStr, AccessForVehicleProperty,
&configDecl.config.access, errors);
//解析changeMode
parseAccessChangeMode(propJsonValue, "changeMode", propId, propStr,
ChangeModeForVehicleProperty, &configDecl.config.changeMode, errors);
...
tryParseJsonValueToVariable(propJsonValue, "configString", /*optional=*/true,
&configDecl.config.configString, errors);
tryParseJsonArrayToVariable(propJsonValue, "configArray", /*optional=*/true,
&configDecl.config.configArray, errors);
//解析默认值
parsePropValues(propJsonValue, "defaultValue", &configDecl.initialValue, errors);
tryParseJsonValueToVariable(propJsonValue, "minSampleRate", /*optional=*/true,
&configDecl.config.minSampleRate, errors);
tryParseJsonValueToVariable(propJsonValue, "maxSampleRate", /*optional=*/true,
&configDecl.config.maxSampleRate, errors);
parseAreas(propJsonValue, "areas", &configDecl, errors);
...
return configDecl;
}
，这一步会按照json文件中的每个property的配置按照顺序解析json键值对。重点关注parseAccessChangeMode方法和parsePropValues函数。
解析 access / change mode
首先查看parseAccessChangeMode方法：
void JsonConfigParser::parseAccessChangeMode(
const Json::Value& parentJsonNode, const std::string& fieldName, int propId,
const std::string& propStr, const std::unordered_map<VehicleProperty, T>& defaultMap,
T* outPtr, std::vector<std::string>* errors) {
...
if (parentJsonNode.isMember(fieldName)) {
//从Json文件中加载access/change mode
auto result = mValueParser.parseValue<int32_t>(fieldName, parentJsonNode[fieldName]);
...
*outPtr = static_cast<T>(result.value());
return;
}
//从defaultMap中加载access/change mode
auto it = defaultMap.find(static_cast<VehicleProperty>(propId));
...
*outPtr = it->second;
return;
}
，这一步会从Json文件中加载access/change mode，如果Json文件中没有定义access/change mode的话，则会从传入的defaultMap中加载access/ change mode。 观察AccessForVehicleProperty或ChangeModeForVehicleProperty所在的文件，在文件中可以看到下面一段注释：
// AccessForVehicleProperty.h
/**
* DO NOT EDIT MANUALLY!!!
*
* Generated by tools/generate_annotation_enums.py.
*/
，查看/hardware/interfaces/automotive/vehicle/tools/generate_annotation_enums.py：
...
RE_COMMENT_BEGIN = re.compile("\s*\/\*\*?")
RE_COMMENT_END = re.compile("\s*\*\/")
RE_CHANGE_MODE = re.compile("\s*\* @change_mode (\S+)\s*")
RE_ACCESS = re.compile("\s*\* @access (\S+)\s*")
RE_VALUE = re.compile("\s*(\w+)\s*=(.*)")
...
class Converter:
def __init__(self, name, annotation_re):
self.name = name
self.annotation_re = annotation_re
def convert(self, input, output, header, footer, cpp):
processing = False
in_comment = False
content = LICENSE + header
annotation = None
id = 0
with open(input, 'r') as f:
for line in f.readlines():
...
# 注释开始 /**
if RE_COMMENT_BEGIN.match(line):
in_comment = True
# 注释结束 */
if RE_COMMENT_END.match(line):
in_comment = False
if in_comment:
# 在注释中匹配 @change_mode XXX 或 @access XXX
match = self.annotation_re.match(line)
# 解析其第二个字段 XXX
if match:
annotation = match.group(1)
else:
# 注释结束，匹配属性名
match = RE_VALUE.match(line)
if match:
prop_name = match.group(1)
...
# 生成代码
if cpp:
annotation = annotation.replace(".", "::")
content += (TAB + TAB + "{VehicleProperty::" + prop_name + ", " +
annotation + "},")
else:
content += (TAB + TAB + "Map.entry(VehicleProperty." + prop_name + ", " +
annotation + "),")
id += 1
...
，这段脚本的作用是从VehicleProperty.aidl文件中解析注释并生成C++或Java代码。给定一个属性如：
/**
* VIN of vehicle
*
* @change_mode VehiclePropertyChangeMode.STATIC
* @access VehiclePropertyAccess.READ
*/
INFO_VIN = 0x0100 + 0x10000000 + 0x01000000
+ 0x00100000, // VehiclePropertyGroup:SYSTEM,VehicleArea:GLOBAL,VehiclePropertyType:STRING
，则会在ChangeModeForVehicleProperty和AccessForVehicleProperty中生成条目：
//change mode
std::unordered_map<VehicleProperty, VehiclePropertyChangeMode> ChangeModeForVehicleProperty = {
{VehicleProperty::INFO_VIN, VehiclePropertyChangeMode::STATIC},
...
}
//access
std::unordered_map<VehicleProperty, VehiclePropertyAccess> AccessForVehicleProperty = {
{VehicleProperty::INFO_VIN, VehiclePropertyAccess::READ},
...
}
//change mode
public final class AccessForVehicleProperty {
public static final Map<Integer, Integer> values = Map.ofEntries(
Map.entry(VehicleProperty.INFO_VIN, VehiclePropertyAccess.READ),
...
)
}
//access
public final class ChangeModeForVehicleProperty {
public static final Map<Integer, Integer> values = Map.ofEntries(
Map.entry(VehicleProperty.INFO_VIN, VehiclePropertyChangeMode.STATIC),
...
)
}
注意到，在生成代码时：
content += (TAB + TAB + "{VehicleProperty::" + prop_name + ", " +
annotation + "},")
，此部分VehicleProperty是硬编码在脚本中的，同样的，对于方法parseAccessChangeMode：
void JsonConfigParser::parseAccessChangeMode(
const Json::Value& parentJsonNode, const std::string& fieldName, int propId,
const std::string& propStr, const std::unordered_map<VehicleProperty, T>& defaultMap,
T* outPtr, std::vector<std::string>* errors)
，VehicleProperty也是硬编码在代码中的，如果需要实现自定义的XXXVehicleProperty，则需要重写相应的内容。
***
解析default values
查看parsePropValues方法：
bool JsonConfigParser::parsePropValues(const Json::Value& parentJsonNode,
const std::string& fieldName, RawPropValues* outPtr,
std::vector<std::string>* errors) {
...
success &= tryParseJsonArrayToVariable(jsonValue, "int32Values",
/*optional=*/true, &(outPtr->int32Values), errors);
success &= tryParseJsonArrayToVariable(jsonValue, "floatValues",
/*optional=*/true, &(outPtr->floatValues), errors);
success &= tryParseJsonArrayToVariable(jsonValue, "int64Values",
/*optional=*/true, &(outPtr->int64Values), errors);
success &= tryParseJsonValueToVariable(jsonValue, "stringValue",
/*optional=*/true, &(outPtr->stringValue), errors);
...
}
，调用了tryParseJsonArrayToVariable方法：
bool JsonConfigParser::tryParseJsonArrayToVariable(const Json::Value& parentJsonNode,
const std::string& fieldName,
bool fieldIsOptional, std::vector<T>* outPtr,
std::vector<std::string>* errors) {
...
auto result = mValueParser.parseArray<T>(fieldName, parentJsonNode[fieldName]);
...
*outPtr = std::move(result.value());
return true;
}
，调用了JsonValueParser::parseArray方法：
template <class T>
Result<std::vector<T>> JsonValueParser::parseArray(const std::string& fieldName,
const Json::Value& value) const {
...
std::vector<T> parsedValues;
for (unsigned int i = 0; i < value.size(); i++) {
auto result = parseValue<T>(fieldName, value[i]);
...
parsedValues.push_back(result.value());
}
return std::move(parsedValues);
}
，调用了parseValue方法：
template <class T>
Result<T> JsonValueParser::parseValue(const std::string& fieldName,
const Json::Value& value) const {
//如果value不是字符串格式的
if (!value.isString()) {
return convertValueToType<T>(fieldName, value);
}
//如果value是字符串格式的
auto maybeTypeAndValue = maybeGetTypeAndValueName(value.asString());
...
auto constantParseResult = parseConstantValue(maybeTypeAndValue.value());
...
int constantValue = constantParseResult.value();
return static_cast<T>(constantValue);
}
，上述方法在value不是字符串格式时直接解析为值，如果value不是字符串格式时，首先会调用maybeGetTypeAndValueName方法：
//JsonConfigLoader.h
inline static const std::string DELIMITER = "::";
//JsonConfigLoader.cpp
std::optional<std::pair<std::string, std::string>> JsonValueParser::maybeGetTypeAndValueName(
const std::string& jsonFieldValue) const {
size_t pos = jsonFieldValue.find(DELIMITER);
...
std::string type = jsonFieldValue.substr(0, pos);
std::string valueName = jsonFieldValue.substr(pos + DELIMITER.length(), std::string::npos);
...
return std::make_pair(type, valueName);
}
，这一步回去解析Json文件中类似"FuelType::FUEL_TYPE_UNLEADED"的声明，将其拆分为两部分：type（"FuelType"）和valueName（"FUEL_TYPE_UNLEADED"）。在执行完maybeGetTypeAndValueName后，会调用parseConstantValue：
Result<int> JsonValueParser::parseConstantValue(
const std::pair<std::string, std::string>& typeValueName) const {
const std::string& type = typeValueName.first;
const std::string& valueName = typeValueName.second;
auto it = mConstantParsersByType.find(type);
...
auto result = it->second->parseValue(valueName);
...
return result;
}
，这一步会在mConstantParsersByType中找到与type对应的ConstantParser对象，mConstantParsersByType在JsonValueParser的构造函数中被填充：
JsonValueParser::JsonValueParser() {
...
mConstantParsersByType["VehicleProperty"] = std::make_unique<ConstantParser<VehicleProperty>>();
...
}
，ConstantParser的定义如下：
template <class T>
class ConstantParser final : public ConstantParserInterface {
public:
ConstantParser() {
for (const T& v : ndk::enum_range<T>()) {
std::string name = aidl::android::hardware::automotive::vehicle::toString(v);
...
mValueByName[name] = toInt(v);
}
}
~ConstantParser() = default;
Result<int> parseValue(const std::string& name) const override {
auto it = mValueByName.find(name);
...
return it->second;
}
private:
std::unordered_map<std::string, int> mValueByName;
};
，其parseValue方法会从mValueByName中找到name对应的值，而构造ConstantParser时添加。
注意到，在ConstantParser中，使用了aidl::android::hardware::automotive::vehicle::toString，对于自定义的XXXVehicleProperty，是无法解析的，需要重写该类。
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