1.1 RCTRootView

一个RCTRootView持有一个RCTBridge成员变量

RCTRootView : UIView
  RCTBridge *bridge;
  UIViewController *reactViewController;
  UIView *contentView;
  UIView *loadingView;

1.2 RCTBridge

一个RCTBridge持有一个RCTCxxBridge成员变量

RCTBridge.h
 @interface RCTBridge : NSObject <RCTInvalidating>

RCTBridge+Private.h
@interface RCTBridge ()
   RCTBridge *batchedBridge;
@end

RCTBridge.m
- (Class)bridgeClass
  return [RCTCxxBridge class];

- (void)setUp
  Class bridgeClass = self.bridgeClass;
  self.batchedBridge = [[bridgeClass alloc] initWithParentBridge:self];
  [self.batchedBridge start];

1.3 RCTCxxBridge

RCTCxxBridge继承自RCTBridge，是RCTBridge的一个变量，拥有弱引用parentBridge指向RCTBridge变量

RCTBridge+Private.h
@interface RCTCxxBridge:RCTBridge

RCTCxxBridge.mm
@interface RCTCxxBridge()
RCTBridge *parentBridge;
@end
//@interface ViewController()后面 ，@end前面的是类扩展，就是创建本类中似有的属性和方法。其他类不能使用的

2.核心流程

2.1 native注册模块表

一个native类需要向js暴露的过程，就是向全局静态数组RCTModuleClasses注册自身class的过程。工程启动后，自动生成全局静态数组RCTModuleClasses，储存注册的class

######RCTBridge
声明全局静态数组：
static NSMutableArray<Class> *RCTModuleClasses;

######native类
需要做到以下两点，
1.实现RCTBridgeModule协议
2.在m文件中放置RCT_EXPORT_MODULE()代码。

RCT_EXPORT_MODULE宏给native类置入load函数。native类在加载过程中，可以自动向RCTModuleClasses注册自身Class。实例如下

ClassA.h
#import <React/RCTBridgeModule.h>
@interface ClassA <RCTBridgeModule>
@end

ClassA.m
RCT_EXPORT_MODULE() ==>
extern __attribute__((visibility("default"))) 
void RCTRegisterModule(Class);  
+ (void)load { RCTRegisterModule(self); }

========================================
宏定义
RCTBridgeModule.h
#define RCT_EXPORT_MODULE(js_name) RCT_EXTERN void RCTRegisterModule(Class); + (NSString *)moduleName { return @#js_name; } + (void)load { RCTRegisterModule(self); }

#define RCT_EXPORT_MODULE(js_name) RCT_EXTERN void RCTRegisterModule(Class);  + (NSString *)moduleName { return @#js_name; }  + (void)load { RCTRegisterModule(self); }

RCTDefindes.h
#define RCT_EXTERN extern __attribute__((visibility("default")))

注册
RCTBridge.m
static NSMutableArray<Class> *RCTModuleClasses;
void RCTRegisterModule(Class moduleClass)
   [RCTModuleClasses addObject:moduleClass];

2.2 RCTCxxBridge初始化模块表

RCTCxxBridge有三个成员变量，_moduleDataByName，_moduleDataByID，_moduleClassesByID

RCTCxxBridge
NSMutableDictionary<NSString *,RCTModuleData *> *_moduleDataByName; //字典，name：RCTModuleData键值对
NSMutableArray<RCTModuleData *> *_moduleDataByID; //RCTModuleData数组
NSMutableArray<Class> *_moduleClassesByID; //Class数组
- (void)start 
  [self _initModules:RCTGetModuleClasses() withDispatchGroup:prepareBridge lazilyDiscovered:NO];

- (void)_initModules:(NSArray<id<RCTBridgeModule>> *)modules
   withDispatchGroup:(dispatch_group_t)dispatchGroup
    lazilyDiscovered:(BOOL)lazilyDiscovered
  NSArray<RCTModuleData *> *moduleDataById = [self registerModulesForClasses:modules]; //将modules转换成RCTCxxBridge的模块组

- (NSArray<RCTModuleData *> *)registerModulesForClasses:(NSArray<Class> *)moduleClasses
   for (Class moduleClass in moduleClasses) {
      _moduleDataByName[moduleName] = moduleData;
      [_moduleClassesByID addObject:moduleClass];
      [moduleDataByID addObject:moduleData];
   }
   [_moduleDataByID addObjectsFromArray:moduleDataByID];

2.3 RCTCxxBridge 加载/执行JS资源

- (void)start 
     [self loadSource:^(NSError *error,RCTSource *source)
           {sourceCode = source.data;}]  // 加载JS
     [strongSelf executeSourceCode:sourceCode sync:NO]; //执行JS

- (void)loadSource:(RCTSourceLoadBlock)_onSourceLoad onProgress:(RCTSourceLoadProgressBlock)onProgress
     发送通知RCTBridgeWillDownloadScriptNotification
     RCTSourceLoadBlock onSourceLoad = ^(NSError *error,RCTSource *source) 
     {
            发送通知RCTBridgeDidDownloadScriptNotification：RCTSource
     }
    [RCTJavaScriptLoader loadBundleAtURL:self.bundleURL onProgress:onProgress onComplete:^(NSError *error,RCTSource *source)
     {
          onSourceLoad(error,source);
     }

- (void)executeSourceCode:(NSData *)sourceCode sync:(BOOL)sync
   - (void)executeApplicationScript:(NSData *)script
                             url:(NSURL *)url
                           async:(BOOL)async
  dispatch_block_t completion = ^{
          [self _flushPendingCalls];
          广播通知RCTJavaScriptDidLoadNotification
          [self ensureOnJavaScriptThread:^{
             [self->_displayLink addToRunLoop:[NSRunLoop currentRunLoop]];
          }];
     }

- (void)executeApplicationScript:(NSData *)script
                             url:(NSURL *)url
                           async:(BOOL)async
  if (isRAMBundle(script))
      self->_reactInstance->loadRAMBundle(std::move(registry),std::move(scriptStr),sourceUrlStr.UTF8String,!async);
  else if (self->_reactInstance)
      self->_reactInstance->loadScriptFromString(std::make_unique<NSDataBigString>(script),!async);

- (void)registerAdditionalModuleClasses:(NSArray<Class> *)modules
    |=== - (NSArray<RCTModuleData *> *)registerModulesForClasses:(NSArray<Class> *)moduleClasses
          |---for (Class moduleClass in moduleClasses) 
          {
              NSString *moduleName = RCTBridgeModuleNameForClass(moduleClass);
              moduleData = [[RCTModuleData alloc] initWithModuleClass:moduleClass bridge:self];

          }

[RCTCxxBridge registerExtraModules]

• (void)start
  |--- 广播通知---
  RCTJavaScriptWillStartLoadingNotification：@{@"bridge": self}
  |--- 新建并启动js线程 _jsThread
  |--- 注册moduleClass---
  [self registerExtraModules];
  [self _initModules:RCTGetModuleClasses() withDispatchGroup:prepareBridge lazilyDiscovered:NO];
  |--- 创建工厂并配置---
  std::shared_ptr<JSExecutorFactory> executorFactory;
  |--- 加载js资源---
  [self loadSource:^(NSError error,RCTSource source)
  |--- 执行js---
  [strongSelf executeSourceCode:sourceCode sync:NO];

启动

[AppDelegate didFinishLaunchingWithOptions]
|---获取jsCodeLocation
|---[RCTRootView initWithBundleURL..]
    |---[RCTBridge alloc+init]
        |---设置变量：delegate，bundleURL，moduleProvider,launchOptions
        |---[RCTBridge setUp]
            |---设置变量：bundleURL
            |---[RCTCxxBridge alloc+init]  --> RCTBridge.batchedBridge
            |---[RCTCxxBridge start]

    |---[RCTRootView initWithBridge:...]
          |---注册三个通知，如下
          |---[self bundleFinishedLoading:([_bridge batchedBridge] ?: _bridge)];
                |---RCTRootContentView alloc
                |---[self runApplication:bridge];
                       |---[bridge enqueueJSCall:@"AppRegistry"
                 method:@"runApplication"
                   args:@[moduleName,appParameters]
             completion:NULL];
                |---insertSubview:_contentView

RCTRootView 继承自UIView，内含RCTBridge变量，初始化参数BundleURL/moduleName/Properties/launchOptions。初始化的时候，初始化RCTBridge变量，自我初始化。自我初始化过程：注册三个通知，RCTJavaScriptWillStartLoadingNotification/RCTJavaScriptDidLoadNotification/RCTContentDidAppearNotification

RCTBridge native call js

[RCTBridge enqueueJSCall:(NSString *)module method:(NSString *)method args:(NSArray *)args completion:(dispatch_block_t)completion]
|---[self.batchedBridge enqueueJSCall:module method:method args:args completion:completion];

RCTCxxBridge 成员：
_moduleClassesByID
_moduleDataByID
_moduleDataByName 可变字典：string（moduleName）：RCTModuleData（Data）的键值队
RCTCxxBridge native call js,可以从任意线程中调起

RCTBridge  
- (void)setUp
   URL转换
   self.batchedBridge = [[bridgeClass alloc] initWithParentBridge:self];
   [self.batchedBridge start];

- (void)registerAdditionalModuleClasses:(NSArray<Class> *)modules
   [self.batchedBridge registerAdditionalModuleClasses:modules];

RCTJavaScriptLoader  
+ (void)loadBundleAtURL:(NSURL *)scriptURL onProgress:(RCTSourceLoadProgressBlock)onProgress onComplete:(RCTSourceLoadBlock)onComplete
|---NSData *data = [self attemptSynchronousLoadOfBundleAtURL:scriptURL
                                          runtimeBCVersion:JSNoBytecodeFileFormatVersion
                                              sourceLength:&sourceLength
                                                     error:&error];
|---onComplete(nil,RCTSourceCreate(scriptURL,data,sourceLength));

+ (NSData *)attemptSynchronousLoadOfBundleAtURL:(NSURL *)scriptURL
                               runtimeBCVersion:(int32_t)runtimeBCVersion
                                   sourceLength:(int64_t *)sourceLength
                                          error:(NSError **)error
|---FILE *bundle = fopen(scriptURL.path.UTF8String,"r");
    size_t readResult = fread(&header,sizeof(header),1,bundle);

[RCTCxxBridge enqueueJSCall:(NSString *)module method:(NSString *)method args:(NSArray *)args completion:(dispatch_block_t)completion]
|---

NSInvocation 调用 native 方法

调用原生代码生成UI控件

RCTUIManager RCT_EXPORT_METHOD(createView:(nonnull NSNumber *)reactTag
                                 viewName:(NSString *)viewName
                                  rootTag:(nonnull NSNumber *)rootTag
                                    props:(NSDictionary *)props)
|---createViewBlock
      |---[RCTComponentData createViewWithTag:reactTag];
            |--- [self.manager view]   
                 #此处self.manager是实际需要生成的UI类，如RCTTextView等
                 #所以，所有RN的原生UI都必须实现view功能
      |---RCTUIManager->_viewRegistry[reactTag] = preliminaryCreatedView;  
          #保存至注册数组，reactTag：preliminaryCreatedView
          #RCTUIManager->_viewRegistry 
          # {1 = "<RCTRootContentView: 0x7faf12c015d0; reactTag: 1; frame = (0 0; 414 736); gestureRecognizers = <NSArray: 0x60000024eaf0>; layer = <CALayer: 0x6040002376c0>>";
          # 2 = "<UIView: 0x7faf12f0a6d0; frame = (0 0; 0 0); layer = <CALayer: 0x600000621300>>";}

Instance C++ 类
void Instance::loadRAMBundle(std::unique_ptr<RAMBundleRegistry> bundleRegistry,std::unique_ptr<const JSBigString> startupScript,std::string startupScriptSourceURL,bool loadSynchronously)

RCTModuleMethod C++ 类
通过NSInvocation动态调用相应的OC模块方法

- (id)invokeWithBridge:(RCTBridge *)bridge
                module:(id)module
             arguments:(NSArray *)arguments
   [self processMethodSignature];   //set blocks 
   block(bridge,index,RCTNilIfNull(json(arguments))   //set arguments
   [_invocation invokeWithTarget:module];   //调起函数
   [_invocation getReturnValue:&returnValue];   //获取返回值

RN 支持功能
tabbar，nagigator，text，image，数据库？，ar？，真机调试日志？，网络，摄像头拍照，图片剪裁，音频，视频，下载，

添加RN库

tabbar官方组件 TabBarIOS,TabBarIOS.Item,只支持iOS，弃用流行组件