React Native通讯原理
之前写过一篇文章 ReactNative Android源码分析,在此文章的基础上分析和总结下RN与Native的通讯流程。 1. 通讯框架图先来解析下各个模块的角色与作用: Java层,这块的实现在ReactAndroid中 C++层,这块实现在ReactCommon中,供Android与iOS使用 JS层,实现在Libraries中,RN JS相关的实现在都这个文件夹中 2. C++与JS间通讯Native与JS通讯无非就是Java/OC与JS跨语言间的调用,在分析Native与JS通讯前先来了解下Java/OC与JS跨语言间的调用。 compile 'org.webkit:android-jsc:r174650'
task downloadJSCHeaders(type: Download) {
def jscAPIBaseURL = 'https://svn.webkit.org/repository/webkit/ !svn/bc/174650/trunk/Source/JavaScriptCore/API/'
def jscHeaderFiles = ['JavaScript.h','JSBase.h','JSContextRef.h','JSObjectRef.h','JSRetainPtr.h','JSStringRef.h','JSValueRef.h','WebKitAvailability.h']
def output = new File(downloadsDir,'jsc')
output.mkdirs()
src(jscHeaderFiles.collect { headerName -> "$jscAPIBaseURL$headerName" })
onlyIfNewer true
overwrite false
dest output
}
// Create Android.mk library module based on so files from mvn + include headers fetched from webkit .org
task prepareJSC(dependsOn: downloadJSCHeaders) << {
copy {
from zipTree(configurations.compile.fileCollection { dep -> dep.name == 'android-jsc' }. singleFile)
from {downloadJSCHeaders.dest}
from 'src/main/jni/third-party/jsc/Android.mk'
include 'jni/**/*.so','*.h','Android.mk'
filesMatching('*.h',{ fname -> fname.path = "JavaScriptCore/${fname.path}"})
into "$thirdPartyNdkDir/jsc";
}
}
LOCAL_SRC_FILES := jni/$(TARGET_ARCH_ABI)/libjsc.so
从这里可以看出RN并没有用系统自带的webkit,WebKit主要包括WebCore排版引擎和JSCore引擎,这里主要使用了JSCore引擎,排版交给Native去做。 在RN中通过下面的方法设置native方法和属性: JSObjectSetProperty(m_context,globalObject,jsPropertyName,valueToInject,0,NULL);
这个方法正是上面gradle脚本下载的JSObjectRef.h中,实现在libjsc.so中。这样就可以在Native设置,然后在JS中取出执行,反过来也是同样的。 3. Native与JS通讯#####加载bundle文件 public abstract class ReactNativeHost {
...
/** * Returns the name of the main module. Determines the URL used to fetch the JS bundle * from the packager server. It is only used when dev support is enabled. * This is the first file to be executed once the {@link ReactInstanceManager} is created. * e.g. "index.android" */
protected String getJSMainModuleName() {
return "index.android";
}
/** * Returns a custom path of the bundle file. This is used in cases the bundle should be loaded * from a custom path. By default it is loaded from Android assets,from a path specified * by {@link getBundleAssetName}. * e.g. "file://sdcard/myapp_cache/index.android.bundle" */
protected @Nullable String getJSBundleFile() {
return null;
}
/** * Returns the name of the bundle in assets. If this is null,and no file path is specified for * the bundle,the app will only work with {@code getUseDeveloperSupport} enabled and will * always try to load the JS bundle from the packager server. * e.g. "index.android.bundle" */
protected @Nullable String getBundleAssetName() {
return "index.android.bundle";
}
/** * Returns whether dev mode should be enabled. This enables e.g. the dev menu. */
protected abstract boolean getUseDeveloperSupport();
...
}
ReactNativeHost中的这些方法会根据需要在Application中重载,这些方法决定了从哪里加载Bundle,方法的注释写的非常清晰,不再介绍了,先看一下流程图: JSBundleLoader从哪里加载,也是根据文件的位置,可以看看其loadScript方法,最终都会调用CatalystIntance去加载,有三个实现 /* package */ native void loadScriptFromAssets(AssetManager assetManager,String assetURL);
/* package */ native void loadScriptFromFile(String fileName,String sourceURL);
/* package */ native void loadScriptFromOptimizedBundle(String path,String sourceURL,int flags);
最后一个支持加载优化后的Bundle,目前没有用到。这些方法都是c++实现,主要看一下前两个 void CatalystInstanceImpl::loadScriptFromAssets(jobject assetManager,const std::string& assetURL) {
const int kAssetsLength = 9; // strlen("assets://");
auto sourceURL = assetURL.substr(kAssetsLength);
auto manager = react::extractAssetManager(assetManager);
auto script = react::loadScriptFromAssets(manager,sourceURL);
if (JniJSModulesUnbundle::isUnbundle(manager,sourceURL)) {
instance_->loadUnbundle(
folly::make_unique<JniJSModulesUnbundle>(manager,sourceURL),std::move(script),sourceURL);
return;
} else {
instance_->loadScriptFromString(std::move(script),sourceURL);
}
}
void CatalystInstanceImpl::loadScriptFromFile(jni::alias_ref<jstring> fileName,const std::string& sourceURL) {
return instance_->loadScriptFromFile(fileName ? fileName->toStdString() : "",sourceURL);
}
从assets中加载就是先读取bundle的内容,当作一个字符串,这里有一个UnBundle,是RN打包的一种方式,除了生成整合JS文件index.android.bundle外,还会生成各个单独的未整合JS文件(但会被优化),全部放在js-modules目录下,同时会生成一个名为UNBUNDLE的标识文件,一并放在其中。UNBUNDLE标识文件的前4个字节固定为0xFB0BD1E5,用于加载前的校验。需要注意的是,js-modules目录会一并打包到apk的assets文件夹中,这里就是处理这种情况的,后面具体的加载暂不分析,可以参考这篇文章。
下载完成后调用CatalystInstance.loadScriptFromFile(),传递缓存后的径路,这个方法也是先读取文件内容,存为字符串,也是调用loadScriptFromString void Instance::loadScriptFromString(std::unique_ptr<const JSBigString> string,std::string sourceURL) {
callback_->incrementPendingJSCalls();
SystraceSection s("reactbridge_xplat_loadScriptFromString","sourceURL",sourceURL);
// TODO mhorowitz: ReactMarker around loadApplicationScript
nativeToJsBridge_->loadApplicationScript(std::move(string),std::move(sourceURL));
}
--------------------------------------
void NativeToJsBridge::loadApplicationScript(std::unique_ptr<const JSBigString> script,std::string sourceURL) {
// TODO(t11144533): Add assert that we are on the correct thread
m_mainExecutor->loadApplicationScript(std::move(script),std::move(sourceURL));
}
loadApplicationScript的作用请参考ReactNative Android源码分析。 #####如何调用JS 在Native中调用JS的方式如下 : ReactContext.getJSModule(JSModule类名.class).方法名(params);
ReactContext调用的是CatalystInstance的同名方法 @Override
public <T extends JavaScriptModule> T getJSModule(Class<T> jsInterface) {
return getJSModule(mMainExecutorToken,jsInterface);
}
@Override
public <T extends JavaScriptModule> T getJSModule(ExecutorToken executorToken,Class<T> jsInterface) {
return Assertions.assertNotNull(mJSModuleRegistry)
.getJavaScriptModule(this,executorToken,jsInterface);
}
mMainExecutorToken是在initializeBridge时创建的,根据注释是和web workers相关,是JS多线程相关的,即使用Token来区分线程。当前这种情况使用mMainExecutorToken就可以。看一下CatalystInstance的实现: public synchronized <T extends JavaScriptModule> T getJavaScriptModule(
CatalystInstance instance,ExecutorToken executorToken,Class<T> moduleInterface) {
HashMap<Class<? extends JavaScriptModule>,JavaScriptModule> instancesForContext =
mModuleInstances.get(executorToken);
if (instancesForContext == null) {
instancesForContext = new HashMap<>();
mModuleInstances.put(executorToken,instancesForContext);
}
JavaScriptModule module = instancesForContext.get(moduleInterface);
if (module != null) {
return (T) module;
}
JavaScriptModuleRegistration registration =
Assertions.assertNotNull(
mModuleRegistrations.get(moduleInterface),"JS module " + moduleInterface.getSimpleName() + " hasn't been registered!");
JavaScriptModule interfaceProxy = (JavaScriptModule) Proxy.newProxyInstance(
moduleInterface.getClassLoader(),new Class[]{moduleInterface},new JavaScriptModuleInvocationHandler(executorToken,instance,registration));
instancesForContext.put(moduleInterface,interfaceProxy);
return (T) interfaceProxy;
}
在CatalystInstance创建的时候会把所有JavaScriptModule都收集到JavaScriptModuleRegistry的Map(mModuleRegistrations)中。而mModuleInstances是缓存已经调用过的JS Module的代理对象,如果已经调用过,则从map中直接返回,否则创建其代理对象,然后缓存起来。 @Override
public @Nullable Object invoke(Object proxy,Method method,@Nullable Object[] args) throws Throwable { ExecutorToken executorToken = mExecutorToken.get(); if (executorToken == null) { FLog.w(ReactConstants.TAG,"Dropping JS call,ExecutorToken went away..."); return null; } NativeArray jsArgs = args != null ? Arguments.fromJavaArgs(args) : new WritableNativeArray();
mCatalystInstance.callFunction(
executorToken,mModuleRegistration.getName(),method.getName(),jsArgs );
return null;
}
这个调用流程已经在ReactNative Android源码分析中分析了。这次会走到JS的MessageQueue.callFunctionReturnFlushedQueue()中了。 JS接收调用和处理先来解释下为什么会走到callFunctionReturnFlushedQueue。 Object.defineProperty(global,"__fbBatchedBridge",{configurable:!0,value:BatchedBridge})
这里明明是BatchedBridge,为什么说是MessageQueue的对象呢,原来在BatchedBridge.js中有这样几句代码 const BatchedBridge = new MessageQueue(
() => global.__fbBatchedBridgeConfig,serializeNativeParams
);
void JSCExecutor::bindBridge() throw(JSException) {
auto global = Object::getGlobalObject(m_context);
auto batchedBridgeValue = global.getProperty("__fbBatchedBridge");
if (batchedBridgeValue.isUndefined()) {
throwJSExecutionException("Could not get BatchedBridge,make sure your bundle is packaged correctly");
}
auto batchedBridge = batchedBridgeValue.asObject();
m_callFunctionReturnFlushedQueueJS = batchedBridge.getProperty("callFunctionReturnFlushedQueue"). asObject();
m_invokeCallbackAndReturnFlushedQueueJS = batchedBridge.getProperty( "invokeCallbackAndReturnFlushedQueue").asObject();
m_flushedQueueJS = batchedBridge.getProperty("flushedQueue").asObject();
}
这里会把MessageQueue的三个方法会当作对象保存在c++中,当我们调用JS的方法时会直接用到。 void JSCExecutor::callFunction(const std::string& moduleId,const std::string& methodId,const folly::dynamic& arguments) {
try {
auto result = m_callFunctionReturnFlushedQueueJS->callAsFunction({
Value(m_context,String::createExpectingAscii(moduleId)),Value(m_context,String::createExpectingAscii(methodId)),Value::fromDynamic(m_context,std::move(arguments))
});
auto calls = Value(m_context,result).toJSONString();
m_delegate->callNativeModules(*this,std::move(calls),true);
} catch (...) {
std::throw_with_nested(std::runtime_error("Error calling function: " + moduleId + ":" + methodId));
}
}
Value Object::callAsFunction(JSObjectRef thisObj,int nArgs,const JSValueRef args[]) const {
JSValueRef exn;
JSValueRef result = JSObjectCallAsFunction(m_context,m_obj,thisObj,nArgs,args,&exn);
if (!result) {
std::string exceptionText = Value(m_context,exn).toString().str();
throwJSExecutionException("Exception calling object as function: %s",exceptionText.c_str());
}
return Value(m_context,result);
}
最终还是通过JavaScriptCore的方法JSObjectCallAsFunction来调用JS的。下面就好办了,直接分析JS代码吧。 在callFunctionReturnFlushedQueue这个方法主要调用了__callFunction,来看一下它的实现: __callFunction(module: string,method: string,args: any) {
...
const moduleMethods = this._callableModules[module];
...
const result = moduleMethods[method].apply(moduleMethods,args);
Systrace.endEvent();
return result;
}
方法是从_callableModules中取出来的,那他的值是从哪里来的呢,看了下这个文件原来答案是有往里添加的方法 registerCallableModule(name,methods) {
this._callableModules[name] = methods;
}
也就是说所有的JS Module都需要把该Module中可供Native调用的方法都放到这里来,这样才能够执行。以AppRegistry.js为例,来看看它是怎么往里添加的 var AppRegistry = {
registerConfig: function(config: Array<AppConfig>) {...},registerComponent: function(appKey: string,getComponentFunc: ComponentProvider): string {...},registerRunnable: function(appKey: string,func: Function): string {...},getAppKeys: function(): Array<string> {...},runApplication: function(appKey: string,appParameters: any): void {...},unmountApplicationComponentAtRootTag: function(rootTag : number) {...},};
BatchedBridge.registerCallableModule(
'AppRegistry',AppRegistry
);
到这里Native调用JS就已经完成了。 4. JS与Native通讯JS处理Native Module列表在ReactNative Android源码分析中分析了Native的初始化流程,这里总结一下对Native 模块的处理。 那么问题来了,在JS中只能取到Native Module的名字,怎么调用它的方法呢。下面来分析下这个问题。 void JSCExecutor::initOnJSVMThread() throw(JSException) {
....
installNativeHook<&JSCExecutor::nativeRequireModuleConfig>("nativeRequireModuleConfig");
installNativeHook<&JSCExecutor::nativeFlushQueueImmediate>("nativeFlushQueueImmediate");
...
}
JSValueRef JSCExecutor::nativeRequireModuleConfig(
size_t argumentCount,const JSValueRef arguments[]) {
if (argumentCount != 1) {
throw std::invalid_argument("Got wrong number of args");
}
std::string moduleName = Value(m_context,arguments[0]).toString().str();
folly::dynamic config = m_delegate->getModuleConfig(moduleName);
return Value::fromDynamic(m_context,config);
}
从nativeRequireModuleConfig的入参和返回结果就可以看出来 接着来分析下JS是如何处理Native Module的。入口是在MessageQueue.js中处理的。 class MessageQueue {
constructor(configProvider: () => Config,serializeNativeParams: boolean) { .... lazyProperty(this,'RemoteModules',() => { const {remoteModuleConfig} = configProvider(); const modulesConfig = this._genModulesConfig(remoteModuleConfig); const modules = this._genModules(modulesConfig) ... return modules; }); } ... function lazyProperty(target: Object,name: string,f: () => any) { Object.defineProperty(target,name,{ configurable: true,enumerable: true,get() { const value = f(); Object.defineProperty(target,writeable: true,value: value,}); return value; } }); }
在它的构造函数中定义了一个RemoteModules的属性,使用了懒加载的机制,只有真正使用的时候才会为其赋值。返回的是所有Modle列表,只添加了module id,其他信息并没有。 这个RemoteModules是在哪里使用,Module的其他信息又是怎么获取呢,路漫漫其修远兮,接着分析吧 const BatchedBridge = require('BatchedBridge');
const RemoteModules = BatchedBridge.RemoteModules;
...
/**
* Define lazy getters for each module.
* These will return the module if already loaded,or load it if not.
*/
const NativeModules = {};
Object.keys(RemoteModules).forEach((moduleName) => { Object.defineProperty(NativeModules,moduleName,get: () => { let module = RemoteModules[moduleName]; if (module && typeof module.moduleID === 'number' && global.nativeRequireModuleConfig) { // The old bridge (still used by iOS) will send the config as // a JSON string that needs parsing,so we set config according // to the type of response we got. const rawConfig = global.nativeRequireModuleConfig(moduleName); const config = typeof rawConfig === 'string' ? JSON.parse(rawConfig) : rawConfig; module = config && BatchedBridge.processModuleConfig(config,module.moduleID); RemoteModules[moduleName] = module; } Object.defineProperty(NativeModules,value: module,}); return module; },}); }); module.exports = NativeModules;
这块会遍历RemoteModules中所有的模块名,每个模块名都定义一个对象,使用的时候才会为其赋值。看到在赋值的时候会调用c++的nativeRequireModuleConfig,也就是获取每个Module的详细信息。 folly::dynamic ModuleRegistry::getConfig(const std::string& name) {
SystraceSection s("getConfig","module",name);
auto it = modulesByName_.find(name);
if (it == modulesByName_.end()) {
return nullptr;
}
CHECK(it->second < modules_.size());
NativeModule* module = modules_[it->second].get();
// string name,[object constants,] array methodNames (methodId is index),[array asyncMethodIds]
folly::dynamic config = folly::dynamic::array(name);
{
SystraceSection s("getConstants");
folly::dynamic constants = module->getConstants();
if (constants.isObject() && constants.size() > 0) {
config.push_back(std::move(constants));
}
}
{
SystraceSection s("getMethods");
std::vector<MethodDescriptor> methods = module->getMethods();
folly::dynamic methodNames = folly::dynamic::array;
folly::dynamic asyncMethodIds = folly::dynamic::array;
folly::dynamic syncHookIds = folly::dynamic::array;
for (auto& descriptor : methods) {
methodNames.push_back(std::move(descriptor.name));
if (descriptor.type == "remoteAsync") {
asyncMethodIds.push_back(methodNames.size() - 1);
} else if (descriptor.type == "syncHook") {
syncHookIds.push_back(methodNames.size() - 1);
}
}
if (!methodNames.empty()) {
config.push_back(std::move(methodNames));
config.push_back(std::move(asyncMethodIds));
if (!syncHookIds.empty()) {
config.push_back(std::move(syncHookIds));
}
}
}
if (config.size() == 1) {
// no constants or methods
return nullptr;
} else {
return config;
}
}
这里需要解释两个数据结构,modules_是所有Native模块对象的数组,而modulesByName_是一个Map,key值是模块名字,value是该模块在modules_中的索引值。这个方法返回值是一个数组,它的格式是 [
"Module Name",[Object Constants],[Method Name Array],[Async Method Ids],[Sync Hook Ids]
]
前三个好理解,来解释后两是什么含意,asyncMethod字面意思是异步方法,也就是方法参数是Promise的。而syncHook类的方法,目前是没有遇到,这种方法可以JS线程中直接调用,而其他的方法是扔到后台线程队列,然后等待被调用。 std::vector<MethodDescriptor> getMethods() override {
static auto getMDMethod =
wrapper_->getClass()->getMethod<jni::JList<JMethodDescriptor::javaobject>::javaobject()>(
"getMethodDescriptors");
std::vector<MethodDescriptor> ret;
auto descs = getMDMethod(wrapper_);
for (const auto& desc : *descs) {
static auto nameField =
JMethodDescriptor::javaClassStatic()->getField<jstring>("name");
static auto typeField =
JMethodDescriptor::javaClassStatic()->getField<jstring>("type");
ret.emplace_back(
desc->getFieldValue(nameField)->toStdString(),desc->getFieldValue(typeField)->toStdString()
);
}
return ret;
}
folly::dynamic getConstants() override {
static auto constantsMethod =
wrapper_->getClass()->getMethod<NativeArray::javaobject()>("getConstants");
auto constants = constantsMethod(wrapper_);
if (!constants) {
return nullptr;
} else {
// See JavaModuleWrapper#getConstants for the other side of this hack.
return cthis(constants)->array[0];
}
}
这里的wrapper_是指的JavaModuleWrapper,而wrapper_->getClass()是指的Java类:”Lcom/facebook/react/cxxbridge/JavaModuleWrapper;”,也就是说上面是使用反射,调用JavaModuleWrapper的getMethodDescriptors和getConstants。 @DoNotStrip
public class MethodDescriptor {
@DoNotStrip
Method method;
@DoNotStrip
String signature;
@DoNotStrip
String name;
@DoNotStrip
String type;
}
@DoNotStrip
public List<MethodDescriptor> getMethodDescriptors() {
ArrayList<MethodDescriptor> descs = new ArrayList<>();
for (Map.Entry<String,BaseJavaModule.NativeMethod> entry :
mModule.getMethods().entrySet()) {
MethodDescriptor md = new MethodDescriptor();
md.name = entry.getKey();
md.type = entry.getValue().getType();
BaseJavaModule.JavaMethod method = (BaseJavaModule.JavaMethod) entry.getValue();
mMethods.add(method);
descs.add(md);
}
return descs;
}
mModule.getMethods()是在BaseJavaModule中,也是使用反射查找当前模块的方法,方法必须有@ReactMethod的注解才会收集。最终把拿到的信息封装成一个MethodDescriptor的类。 到这里就已经分析了JS是如何拿到Native模块的详细信息的。 ##### 如何调用Native 这里演示下在JS中如何调用Native的module,先假设一个场景,用户点击一个TextView,然后弹个Toast提示。 class AwesomeProject extends Component { render() { return ( <View style={styles.container}> <Text style={styles.welcome} onPress={onClick} > Welcome to React Native! </Text> <Text style={styles.instructions}> To get started,edit index.android.js </Text> <Text style={styles.instructions}> Double tap R on your keyboard to reload,{'n'} Shake or press menu button for dev menu </Text> <TextInput /> </View> ); } } function onClick(){ var ToastAndroid = require('ToastAndroid') ToastAndroid.show('Click TextView...',ToastAndroid.SHORT); }
来看一下ToastAndroid的实现 var RCTToastAndroid = require('NativeModules').ToastAndroid;
...
var ToastAndroid = {
...
show: function (
message: string,duration: number
): void {
RCTToastAndroid.show(message,duration);
},...
};
这里调用的是RCTToastAndroid.show(),而RCTToastAndroid是从NativeModules中取出的。 在前面分析JS如何收集Native模块的时候会生成modules属性,调用Native方法时就是执行它里面的函数,看一下这个函数是如何生成的 _genMethod(module,method,type) {
let fn = null;
const self = this;
if (type === MethodTypes.remoteAsync) {
...
} else if (type === MethodTypes.syncHook) {
...
} else {
fn = function(...args) {
const lastArg = args.length > 0 ? args[args.length - 1] : null;
const secondLastArg = args.length > 1 ? args[args.length - 2] : null;
const hasSuccCB = typeof lastArg === 'function';
const hasErrorCB = typeof secondLastArg === 'function';
hasErrorCB && invariant(
hasSuccCB,'Cannot have a non-function arg after a function arg.'
);
const numCBs = hasSuccCB + hasErrorCB;
const onSucc = hasSuccCB ? lastArg : null;
const onFail = hasErrorCB ? secondLastArg : null;
args = args.slice(0,args.length - numCBs);
return self.__nativeCall(module,onFail,onSucc);
};
}
fn.type = type;
return fn;
}
就是准备好参数,然后__nativeCall。 __nativeCall(module,params,onSucc) {
if (onFail || onSucc) {
...
onFail && params.push(this._callbackID);
this._callbacks[this._callbackID++] = onFail;
onSucc && params.push(this._callbackID);
this._callbacks[this._callbackID++] = onSucc;
}
var preparedParams = this._serializeNativeParams ? JSON.stringify(params) : params;
...
this._callID++;
this._queue[MODULE_IDS].push(module);
this._queue[METHOD_IDS].push(method);
this._queue[PARAMS].push(preparedParams);
const now = new Date().getTime();
if (global.nativeFlushQueueImmediate &&
now - this._lastFlush >= MIN_TIME_BETWEEN_FLUSHES_MS) {
global.nativeFlushQueueImmediate(this._queue);
this._queue = [[],[],this._callID];
this._lastFlush = now;
}
Systrace.counterEvent('pending_js_to_native_queue',this._queue[0].length);
...
}
把模块名、方法名、调用参数放到数组里存起来,如果上次调用和本次调用想着超过5ms则调用c++的nativeFlushQueueImmediate方法,如果小于5ms就直接返回了。 Native接收调用和处理Native接收JS调用分两种情况: 先来看第一种情况 JSValueRef JSCExecutor::nativeFlushQueueImmediate(
size_t argumentCount,const JSValueRef arguments[]) {
if (argumentCount != 1) {
throw std::invalid_argument("Got wrong number of args");
}
std::string resStr = Value(m_context,arguments[0]).toJSONString();
flushQueueImmediate(std::move(resStr));
return JSValueMakeUndefined(m_context);
}
void JSCExecutor::flushQueueImmediate(std::string queueJSON) {
m_delegate->callNativeModules(*this,std::move(queueJSON),false);
}
再来看一下第二种情况 void JSCExecutor::flush() {
auto result = m_flushedQueueJS->callAsFunction({});
try {
auto calls = Value(m_context,result).toJSONString();
m_delegate->callNativeModules(*this,std::move(calls),true);
} catch (...) {
std::string message = "Error in flush()";
try {
message += ":" + Value(m_context,result).toString().str();
} catch (...) {
// ignored
}
std::throw_with_nested(std::runtime_error(message));
}
}
结果都是一样的,把JS的调用转成一个Json字符串,然后再调用JsToNativeBridge.callNativeModules(). void callNativeModules(
JSExecutor& executor,std::string callJSON,bool isEndOfBatch) override {
ExecutorToken token = m_nativeToJs->getTokenForExecutor(executor);
m_nativeQueue->runOnQueue([this,token,callJSON=std::move(callJSON),isEndOfBatch] {
// An exception anywhere in here stops processing of the batch. This
// was the behavior of the Android bridge,and since exception handling
// terminates the whole bridge,there's not much point in continuing.
for (auto& call : react::parseMethodCalls(callJSON)) {
m_registry->callNativeMethod(
token,call.moduleId,call.methodId,std::move(call.arguments),call.callId);
}
if (isEndOfBatch) {
m_callback->onBatchComplete();
m_callback->decrementPendingJSCalls();
}
});
}
这里根据ModuleId 和 MethodId调用Native模块的方法。m_registry是c++的ModuleRegistry,先介绍它是怎么创建的。在CatalystInstance.initializeBridge()的时候传递一个Java层的ModuleRegistryHolder,同样在c++中也有一个同名的对象,在创建的时候会把Native的Module列表保存起来并创建一个c++的ModuleRegistry,把Native的模块列表也传过去了。 void ModuleRegistry::callNativeMethod(ExecutorToken token,unsigned int moduleId,unsigned int methodId,folly::dynamic&& params,int callId) {
if (moduleId >= modules_.size()) {
throw std::runtime_error(
folly::to<std::string>("moduleId ",moduleId," out of range [0..",modules_.size(),")"));
}
#ifdef WITH_FBSYSTRACE
if (callId != -1) {
fbsystrace_end_async_flow(TRACE_TAG_REACT_APPS,"native",callId);
}
#endif
modules_[moduleId]->invoke(token,methodId,std::move(params));
}
moduleId就是模块在列表中的索引,modules_的类型是 std::vector<std::unique_ptr<NativeModule>> modules_;
也就是在创建ModuleRegistryHolder的时候会根据Java层的ModuleRegistryHolder创建c++的NativeModule。来看一下它的invoke方法 void invoke(ExecutorToken token,unsigned int reactMethodId,folly::dynamic&& params) override {
static auto invokeMethod =
wrapper_->getClass()->getMethod<void(JExecutorToken::javaobject,jint,ReadableNativeArray::javaobject)>("invoke");
invokeMethod(wrapper_,JExecutorToken::extractJavaPartFromToken(token).get(),static_cast<jint>(reactMethodId),ReadableNativeArray::newObjectCxxArgs(std::move(params)).get());
}
这里主要是通过反射,调用JavaModuleWrapper的invoke方法,同时把methodId和参数传过去。 /* package */ class JavaModuleWrapper {
...
private final ArrayList<BaseJavaModule.JavaMethod> mMethods;
...
@DoNotStrip
public void invoke(ExecutorToken token,int methodId,ReadableNativeArray parameters) {
if (mMethods == null || methodId >= mMethods.size()) {
return;
}
mMethods.get(methodId).invoke(mCatalystInstance,parameters);
}
}
在JavaModuleWrapper中有一个List,包含了这个module中所有JS可以调用的方法,methodId就是方法的索引和MessageQueue里获取的模块方法id是一致的。JavaMethod的invoke就是通过反射调用相关的方法。至此JS调用Native的流程就完成了。 欢迎评论,多多交流 (编辑:李大同) 【声明】本站内容均来自网络,其相关言论仅代表作者个人观点,不代表本站立场。若无意侵犯到您的权利,请及时与联系站长删除相关内容! |