• WXSDKInstance -> WXBridgeManager->WXBridgeContext->WXJSCoreBridge->JSContext

• WXSDKInstance -> WXComponentManager

• WXBridgeManager : 对WXBridgeContext进一步封装，提供JS API调用，JS 事件发送，注册Native Call Handler，注册Native模块Handler、注册Native组件Handler、注册Native服务Handler等接口。提供Bridge独立线程，上述接口基本上都在该线程中执行。

• WXComponentManager ：管理着组件的布局，样式等

// WXComponentManager.mm

- (void)_layoutAndSyncUI
{
    [self _layout];
    if(_uiTaskQueue.count > 0){
        [self _syncUITasks];
        _noTaskTickCount = 0;
    } else {
        // suspend display link when there's no task for 1 second, in order to save CPU time.
        _noTaskTickCount ++;
        if (_noTaskTickCount > 60) {
            [self _suspendDisplayLink];
        }
    }
}

- (void)_layout
{
    BOOL needsLayout = NO;

    needsLayout = [_rootComponent needsLayout];

    if (!needsLayout) {
        return;
    }
#ifdef DEBUG
    WXLogDebug(@"flexLayout -> action__ calculateLayout root");
#endif

        std::pair<float, float> renderPageSize;
        renderPageSize.first = self.weexInstance.frame.size.width;
        renderPageSize.second = self.weexInstance.frame.size.height;
        _rootFlexCSSNode->calculateLayout(renderPageSize);
    NSMutableSet<WXComponent *> *dirtyComponents = [NSMutableSet set];
    [_rootComponent _calculateFrameWithSuperAbsolutePosition:CGPointZero gatherDirtyComponents:dirtyComponents];
    [self _calculateRootFrame];

    for (WXComponent *dirtyComponent in dirtyComponents) {
        [self _addUITask:^{
            [dirtyComponent _layoutDidFinish];
        }];
    }
}

• WXSDKInstance : 加载bundle文件，管理、渲染根视图。

• WXSDKManager ：管理WXSDKInstance多实例

//WXSDKInstance.m

- (void)_renderWithMainBundleString:(NSString *)mainBundleString
{
    if (!self.instanceId) {
        WXLogError(@"Fail to find instance！");
        return;
    }
    self.performance.renderTimeOrigin = CACurrentMediaTime()*1000;

    if (![WXUtility isBlankString:self.pageName]) {
        WXLog(@"Start rendering page:%@", self.pageName);
    } else {
        WXLogWarning(@"WXSDKInstance's pageName should be specified.");
        id<WXJSExceptionProtocol> jsExceptionHandler = [WXHandlerFactory handlerForProtocol:@protocol(WXJSExceptionProtocol)];
        if ([jsExceptionHandler respondsToSelector:@selector(onRuntimeCheckException:)]) {
            WXRuntimeCheckException * runtimeCheckException = [WXRuntimeCheckException new];
            runtimeCheckException.exception = @"We highly recommend you to set pageName.\n Using WXSDKInstance * instance = [WXSDKInstance new]; instance.pageName = @\"your page name\" to fix it";
            [jsExceptionHandler onRuntimeCheckException:runtimeCheckException];
        }
    }
    if (!self.userInfo) {
        self.userInfo = [NSMutableDictionary new];
    }
    if (!self.userInfo[@"jsMainBundleStringContentLength"]) {
        self.userInfo[@"jsMainBundleStringContentLength"] = @([mainBundleString length]);
    }
    if (!self.userInfo[@"jsMainBundleStringContentLength"]) {
        self.userInfo[@"jsMainBundleStringContentMd5"] = [WXUtility md5:mainBundleString];
    }

    id<WXPageEventNotifyEventProtocol> pageEvent = [WXSDKEngine handlerForProtocol:@protocol(WXPageEventNotifyEventProtocol)];
    if ([pageEvent respondsToSelector:@selector(pageStart:)]) {
        [pageEvent pageStart:self.instanceId];
    }

    WX_MONITOR_INSTANCE_PERF_START(WXPTFirstScreenRender, self);
    WX_MONITOR_INSTANCE_PERF_START(WXPTAllRender, self);

    NSMutableDictionary *dictionary = [_options mutableCopy];
    if ([WXLog logLevel] >= WXLogLevelLog) {
        dictionary[@"debug"] = @(YES);
    }

    if ([WXDebugTool getReplacedBundleJS]) {
        mainBundleString = [WXDebugTool getReplacedBundleJS];
    }

    //TODO WXRootView
    WXPerformBlockOnMainThread(^{
        _rootView = [[WXRootView alloc] initWithFrame:self.frame];
        _rootView.instance = self;
        if(self.onCreate) {
            self.onCreate(_rootView);
        }
    });
    // ensure default modules/components/handlers are ready before create instance
    [WXSDKEngine registerDefaults];
     [[NSNotificationCenter defaultCenter] postNotificationName:WX_SDKINSTANCE_WILL_RENDER object:self];

    _needDestroy = YES;
    _mainBundleString = mainBundleString;
    if ([self _handleConfigCenter]) {
        NSError * error = [NSError errorWithDomain:WX_ERROR_DOMAIN code:9999 userInfo:nil];
        if (self.onFailed) {
            self.onFailed(error);
        }
        return;
    }

    _needDestroy = YES;
    [WXTracingManager startTracingWithInstanceId:self.instanceId ref:nil className:nil name:WXTExecJS phase:WXTracingBegin functionName:@"renderWithMainBundleString" options:@{@"threadName":WXTMainThread}];
    [[WXSDKManager bridgeMgr] createInstance:self.instanceId template:mainBundleString options:dictionary data:_jsData];
    [WXTracingManager startTracingWithInstanceId:self.instanceId ref:nil className:nil name:WXTExecJS phase:WXTracingEnd functionName:@"renderWithMainBundleString" options:@{@"threadName":WXTMainThread}];

    WX_MONITOR_PERF_SET(WXPTBundleSize, [mainBundleString lengthOfBytesUsingEncoding:NSUTF8StringEncoding], self);
}

//WXBridgeProtocol.h

@protocol WXBridgeProtocol <NSObject>

@property (nonatomic, readonly) JSValue* exception;

/**
 * Executes the js framework code in javascript engine
 * You can do some setup in this method
 */
- (void)executeJSFramework:(NSString *)frameworkScript;

/**
 * Executes the js code in javascript engine
 * You can do some setup in this method
 */
- (void)executeJavascript:(NSString *)script;

/**
 * Executes global js method with specific arguments
 */
- (JSValue *)callJSMethod:(NSString *)method args:(NSArray*)args;

/**
 * Register callback when call native tasks occur
 */
- (void)registerCallNative:(WXJSCallNative)callNative;

/**
 * Reset js engine environment, called when any environment variable is changed.
 */
- (void)resetEnvironment;

// WXJSCoreBridge.m

- (void)executeJSFramework:(NSString *)frameworkScript
{
    WXAssertParam(frameworkScript);
    if (WX_SYS_VERSION_GREATER_THAN_OR_EQUAL_TO(@"8.0")) {
        NSString * fileName = @"native-bundle-main.js";
        if ([WXSDKManager sharedInstance].multiContext) {
            fileName = @"weex-main-jsfm.js";
        }
        [_jsContext evaluateScript:frameworkScript withSourceURL:[NSURL URLWithString:fileName]];
    }else{
        [_jsContext evaluateScript:frameworkScript];
    }
}

- (JSValue *)callJSMethod:(NSString *)method args:(NSArray *)args
{
    WXLogDebug(@"Calling JS... method:%@, args:%@", method, args);
    return [[_jsContext globalObject] invokeMethod:method withArguments:args];
}

- (void)registerCallNative:(WXJSCallNative)callNative
{
    JSValue* (^callNativeBlock)(JSValue *, JSValue *, JSValue *) = ^JSValue*(JSValue *instance, JSValue *tasks, JSValue *callback){
        NSString *instanceId = [instance toString];
        NSArray *tasksArray = [tasks toArray];
        NSString *callbackId = [callback toString];
        WXLogDebug(@"Calling native... instance:%@, tasks:%@, callback:%@", instanceId, tasksArray, callbackId);
        return [JSValue valueWithInt32:(int32_t)callNative(instanceId, tasksArray, callbackId) inContext:[JSContext currentContext]];
    };

    _jsContext[@"callNative"] = callNativeBlock;
}