Weex是如何让JS调用产生原生UIView的？

从官方的Demo，我们知道，要在客户端显示Weex页面，是通过WXSDKInstance的实例实现的。我们先来看看这个类里面都有什么：

@interface WXSDKInstance : NSObject

// 需要渲染的viewController
@property (nonatomic, weak) UIViewController *viewController;

// Native根容器的View是完全受WXSDKInstance控制，开发者无法更改
@property (nonatomic, strong) UIView *rootView;

// 如果组件想固定rootview的frame，可以把这个属性设置为YES，当weex进行layout的时候，就不会改变rootview的frame了。反之设置为NO
@property (nonatomic, assign) BOOL isRootViewFrozen;

/**
 * Which indicates current instance needs to be validated or not to load,default value is false.
 **/
@property (nonatomic, assign) BOOL needValidate;

// weex bundle的scriptURL
@property (nonatomic, strong) NSURL *scriptURL;

// 父Instance
@property (nonatomic, weak) WXSDKInstance *parentInstance;

// 父Instance节点的引用
@property (nonatomic, weak) NSString *parentNodeRef;

// 用来标识当前weex instance独一无二的ID
@property (nonatomic, strong) NSString *instanceId;

/**
 * Which indicates current instance needs to be prerender or not,default value is false.
 **/
@property (nonatomic, assign) BOOL needPrerender;

// 当前weex instance的状态
@property (nonatomic, assign) WXState state;

// 当weex instance完成rootView的创建时的回调block
@property (nonatomic, copy) void (^onCreate)(UIView *);

// 根容器的frame改变时候的回调
@property (nonatomic, copy) void (^onLayoutChange)(UIView *);

// 当weex instance完成渲染时的回调block
@property (nonatomic, copy) void (^renderFinish)(UIView *);

// 当weex instance刷新完成时的回调block
@property (nonatomic, copy) void (^refreshFinish)(UIView *);

// 当weex instance渲染失败时的回调block
@property (nonatomic, copy) void (^onFailed)(NSError *error);

/**
 *  The callback triggered when js occurs runtime error while executing.
 *
 *  @return A block that takes a WXJSExceptionInfo argument, which is the exception info
 **/
@property (nonatomic, copy) void (^onJSRuntimeException)(WXJSExceptionInfo * jsException);

// 当weex instance页面滚动时的回调block
@property (nonatomic, copy) void (^onScroll)(CGPoint contentOffset);

// 当weex instance渲染过程中的回调block
@property (nonatomic, copy) void (^onRenderProgress)(CGRect renderRect);

/**
 * The callback triggered when the bundleJS request finished in the renderWithURL.
 * @return A block that takes response which the server response,request which send to server,data which the server returned and an error
 */
@property (nonatomic, copy) void(^onJSDownloadedFinish)(WXResourceResponse *response,WXResourceRequest *request,NSData *data, NSError* error);

// 当前weex instance的frame
@property (nonatomic, assign) CGRect frame;

// user存储的一些信息
@property (atomic, strong) NSMutableDictionary *userInfo;

// css单元和设备像素的换算比例因子
@property (nonatomic, assign, readonly) CGFloat pixelScaleFactor;

// 是否监测组件的渲染
@property (nonatomic, assign)BOOL trackComponent;
/**
 * Renders weex view with bundle url.
 *
 * @param url The url of bundle rendered to a weex view.
 **/
- (void)renderWithURL:(NSURL *)url;

/**
 * Renders weex view with bundle url and some others.
 *
 * @param url The url of bundle rendered to a weex view.
 *
 * @param options The params passed by user
 *
 * @param data The data the bundle needs when rendered.  Defalut is nil.
 **/
- (void)renderWithURL:(NSURL *)url options:(NSDictionary *)options data:(id)data;

///**
// * Renders weex view with resource request.
// *
// * @param request The resource request specifying the URL to render with.
// *
// * @param options The params passed by user.
// *
// * @param data The data the bundle needs when rendered.  Defalut is nil.
// **/
//- (void)renderWithRequest:(WXResourceRequest *)request options:(NSDictionary *)options data:(id)data;

/**
 * Renders weex view with source string of bundle and some others.
 *
 * @param options The params passed by user.
 *
 * @param data The data the bundle needs when rendered. Defalut is nil.
 **/
- (void)renderView:(NSString *)source options:(NSDictionary *)options data:(id)data;

// forcedReload为YES，每次加载都会从URL重新读取，为NO，会从缓存中读取
- (void)reload:(BOOL)forcedReload;

/**
 * Refreshes current instance with data.
 *
 * @param data The data the bundle needs when rendered.
 **/
- (void)refreshInstance:(id)data;

/**
 * Destroys current instance.
 **/
- (void)destroyInstance;

/**
 * Trigger full GC, for dev and debug only.
 **/
- (void)forceGarbageCollection;

/**
 * get module instance by class
 */
- (id)moduleForClass:(Class)moduleClass;

/**
 * get Component instance by ref, must be called on component thread by calling WXPerformBlockOnComponentThread
 */
- (WXComponent *)componentForRef:(NSString *)ref;

/**
 * Number of components created, must be called on component thread by calling WXPerformBlockOnComponentThread
 */
- (NSUInteger)numberOfComponents;

/**
 * check whether the module eventName is registered
 */
- (BOOL)checkModuleEventRegistered:(NSString*)event moduleClassName:(NSString*)moduleClassName;

/**
 * fire module event;
 * @param module which module you fire event to
 * @param eventName the event name
 * @param params event params
 */
- (void)fireModuleEvent:(Class)module eventName:(NSString *)eventName params:(NSDictionary*)params;

/**
 * fire global event
 */
- (void)fireGlobalEvent:(NSString *)eventName params:(NSDictionary *)params;

/**
 * complete url based with bundle url
 */
- (NSURL *)completeURL:(NSString *)url;

/**
 * application performance statistics
 */
@property (nonatomic, strong) NSString *bizType;
@property (nonatomic, strong) NSString *pageName;
@property (nonatomic, weak) id pageObject;
@property (nonatomic, strong) NSMutableDictionary *performanceDict;

/**
 * Deprecated
 */
@property (nonatomic, strong) NSDictionary *properties DEPRECATED_MSG_ATTRIBUTE();
@property (nonatomic, assign) NSTimeInterval networkTime DEPRECATED_MSG_ATTRIBUTE();
@property (nonatomic, copy) void (^updateFinish)(UIView *);

@end

一个WXSDKInstance就对应一个UIViewController，所以每个Weex的页面都有一个与之对应的WXSDKInstance：

@property (nonatomic, strong) WXSDKInstance *instance;

WXSDKInstance一般通过调用renderWithURL方法来渲染页面。

- (void)p_render {
    [_instance destroyInstance];
    _instance = [[WXSDKInstance alloc] init];
    _instance.viewController = self;
    _instance.frame = (CGRect){CGPointZero, kScreenWidth, kScreenHeight};

    __weak typeof(self) weakSelf = self;
    _instance.onCreate = ^(UIView *view) {
        [weakSelf.weexView removeFromSuperview];
        weakSelf.weexView = view;
        [weakSelf.view addSubview:weakSelf.weexView];
    };

    _instance.onFailed = ^(NSError *error) {
        //process failure
    };

    _instance.renderFinish = ^ (UIView *view) {
        //process renderFinish
    };

    if (!self.url) {
        WXLogError(@"error: render url is nil");
        return;
    }
[_instance renderWithURL:self.url options:@{@"bundleUrl":[self.url absoluteString]} data:nil];
}

由于WXSDKInstance是支持实时刷新，所以在创建的时候需要先销毁掉原来的，再创建一个新的。

WXSDKInstance支持设置各种状态时候的回调callback函数，具体支持哪些状态，可以看WXSDKInstance的定义。

Weex支持从本地加载JS，也支持从服务器加载JS。如果从本地加载，那么可以用下面的方法，从本地加载一个JSBundle。

- (void)loadLocalBundle:(NSURL *)url
{
    NSURL * localPath = nil;
    NSMutableArray * pathComponents = nil;
    if (self.url) {
        pathComponents =[NSMutableArray arrayWithArray:[url.absoluteString pathComponents]];
        [pathComponents removeObjectsInRange:NSRangeFromString(@"0 3")];
        [pathComponents replaceObjectAtIndex: withObject:@"bundlejs"];

        NSString *filePath = [NSString stringWithFormat:@"%@/%@",[NSBundle mainBundle].bundlePath,[pathComponents componentsJoinedByString:@"/"]];
        localPath = [NSURL fileURLWithPath:filePath];
    }else {
        NSString *filePath = [NSString stringWithFormat:@"%@/bundlejs/index.js",[NSBundle mainBundle].bundlePath];
        localPath = [NSURL fileURLWithPath:filePath];
    }

    NSString *bundleUrl = [NSURL fileURLWithPath:[NSString stringWithFormat:@"%@/bundlejs/",[NSBundle mainBundle].bundlePath]].absoluteString;
[_instance renderWithURL:localPath options:@{@"bundleUrl":bundleUrl} data:nil];
}

最后渲染页面就是通过调用renderWithURL:options:data:实现的。

- (void)renderWithURL:(NSURL *)url options:(NSDictionary *)options data:(id)data
{
    if (!url) {
        WXLogError(@"Url must be passed if you use renderWithURL");
        return;
    }

    self.needValidate = [[WXHandlerFactory handlerForProtocol:@protocol(WXValidateProtocol)] needValidate:url];

    WXResourceRequest *request = [WXResourceRequest requestWithURL:url resourceType:WXResourceTypeMainBundle referrer:@"" cachePolicy:NSURLRequestUseProtocolCachePolicy];
    [self _renderWithRequest:request options:options data:data];
    [WXTracingManager startTracingWithInstanceId:self.instanceId ref:nil className:nil name:WXTNetworkHanding phase:WXTracingBegin functionName:@"renderWithURL" options:@{@"bundleUrl":url?[url absoluteString]:@"",@"threadName":WXTMainThread}];
}

在WXSDKInstance调用renderWithURL:options:data:方法的时候，会生成一个WXResourceRequest。

@interface WXResourceRequest : NSMutableURLRequest

@property (nonatomic, strong) id taskIdentifier;
@property (nonatomic, assign) WXResourceType type;

@property (nonatomic, strong) NSString *referrer;
@property (nonatomic, strong) NSString *userAgent;

+ (instancetype)requestWithURL:(NSURL *)url
                  resourceType:(WXResourceType)type
                      referrer:(NSString *)referrer
                   cachePolicy:(NSURLRequestCachePolicy)cachePolicy;

@end

WXResourceRequest其实也就是对NSMutableURLRequest的一层封装。

下面来分析一下最核心的函数renderWithURL:options:data:（以下的代码实现在源码的基础上略有删减，源码太长，删减以后并不影响阅读）

- (void)_renderWithRequest:(WXResourceRequest *)request options:(NSDictionary *)options data:(id)data;
{
    NSURL *url = request.URL;
    _scriptURL = url;
    _jsData = data;
    NSMutableDictionary *newOptions = [options mutableCopy] ?: [NSMutableDictionary new];

    if (!newOptions[bundleUrlOptionKey]) {
        newOptions[bundleUrlOptionKey] = url.absoluteString;
    }
    // compatible with some wrong type, remove this hopefully in the future.
    if ([newOptions[bundleUrlOptionKey] isKindOfClass:[NSURL class]]) {
        WXLogWarning(@"Error type in options with key:bundleUrl, should be of type NSString, not NSURL!");
        newOptions[bundleUrlOptionKey] = ((NSURL*)newOptions[bundleUrlOptionKey]).absoluteString;
    }
    _options = [newOptions copy];

    if (!self.pageName || [self.pageName isEqualToString:@""]) {
        self.pageName = url.absoluteString ? : @"";
    }

    request.userAgent = [WXUtility userAgent];

    WX_MONITOR_INSTANCE_PERF_START(WXPTJSDownload, self);
    __weak typeof(self) weakSelf = self;
_mainBundleLoader = [[WXResourceLoader alloc] initWithRequest:request];;
// 请求完成的回调
_mainBundleLoader.onFinished = ^(WXResourceResponse *response, NSData *data) {
        __strong typeof(weakSelf) strongSelf = weakSelf;
        NSError *error = nil;
        if ([response isKindOfClass:[NSHTTPURLResponse class]] && ((NSHTTPURLResponse *)response).statusCode != ) {
            error = [NSError errorWithDomain:WX_ERROR_DOMAIN
                                        code:((NSHTTPURLResponse *)response).statusCode
                                    userInfo:@{@"message":@"status code error."}];
            if (strongSelf.onFailed) {
                strongSelf.onFailed(error);
            }
        }

        if (strongSelf.onJSDownloadedFinish) {
            strongSelf.onJSDownloadedFinish(response, request, data, error);
        }

        if (error) {
            WXJSExceptionInfo * jsExceptionInfo = [[WXJSExceptionInfo alloc] initWithInstanceId:@"" bundleUrl:[request.URL absoluteString] errorCode:[NSString stringWithFormat:@"%d", WX_KEY_EXCEPTION_JS_DOWNLOAD] functionName:@"_renderWithRequest:options:data:" exception:[error localizedDescription]  userInfo:nil];
            [WXExceptionUtils commitCriticalExceptionRT:jsExceptionInfo];
            return;
        }

        if (!data) {
            NSString *errorMessage = [NSString stringWithFormat:@"Request to %@ With no data return", request.URL];
            WX_MONITOR_FAIL_ON_PAGE(WXMTJSDownload, WX_ERR_JSBUNDLE_DOWNLOAD, errorMessage, strongSelf.pageName);

            WXJSExceptionInfo * jsExceptionInfo = [[WXJSExceptionInfo alloc] initWithInstanceId:@"" bundleUrl:[request.URL absoluteString] errorCode:[NSString stringWithFormat:@"%d", WX_KEY_EXCEPTION_JS_DOWNLOAD] functionName:@"_renderWithRequest:options:data:" exception:@"no data return"  userInfo:nil];
            [WXExceptionUtils commitCriticalExceptionRT:jsExceptionInfo];

            if (strongSelf.onFailed) {
                strongSelf.onFailed(error);
            }
            return;
        }

        NSString *jsBundleString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        if (!jsBundleString) {
            WX_MONITOR_FAIL_ON_PAGE(WXMTJSDownload, WX_ERR_JSBUNDLE_STRING_CONVERT, @"data converting to string failed.", strongSelf.pageName)
            return;
        }
        if (!strongSelf.userInfo) {
            strongSelf.userInfo = [NSMutableDictionary new];
        }
        strongSelf.userInfo[@"jsMainBundleStringContentLength"] = @([jsBundleString length]);
        strongSelf.userInfo[@"jsMainBundleStringContentMd5"] = [WXUtility md5:jsBundleString];

        WX_MONITOR_SUCCESS_ON_PAGE(WXMTJSDownload, strongSelf.pageName);
        WX_MONITOR_INSTANCE_PERF_END(WXPTJSDownload, strongSelf);

        [strongSelf _renderWithMainBundleString:jsBundleString];
        [WXTracingManager setBundleJSType:jsBundleString instanceId:weakSelf.instanceId];
    };
    // 请求失败的回调
_mainBundleLoader.onFailed = ^(NSError *loadError) {
        NSString *errorMessage = [NSString stringWithFormat:@"Request to %@ occurs an error:%@", request.URL, loadError.localizedDescription];

        WX_MONITOR_FAIL_ON_PAGE(WXMTJSDownload, [loadError.domain isEqualToString:NSURLErrorDomain] && loadError.code == NSURLErrorNotConnectedToInternet ? WX_ERR_NOT_CONNECTED_TO_INTERNET : WX_ERR_JSBUNDLE_DOWNLOAD, errorMessage, weakSelf.pageName);

        if (weakSelf.onFailed) {
            weakSelf.onFailed(error);
        }
    };

    [_mainBundleLoader start];
}

归结起来干了2件事情，第一步，生成了WXResourceLoader，并设置了它的onFinished和onFailed回调。第二步调用了start方法。

在WXSDKInstance中强持有了一个WXResourceLoader，WXResourceLoader的定义如下：

@interface WXResourceLoader : NSObject

@property (nonatomic, strong) WXResourceRequest *request;

@property (nonatomic, copy) void (^onDataSent)(unsigned long long /* bytesSent */, unsigned long long /* totalBytesToBeSent */);
@property (nonatomic, copy) void (^onResponseReceived)(const WXResourceResponse *);
@property (nonatomic, copy) void (^onDataReceived)(NSData *);
@property (nonatomic, copy) void (^onFinished)(const WXResourceResponse *, NSData *);
@property (nonatomic, copy) void (^onFailed)(NSError *);

- (instancetype)initWithRequest:(WXResourceRequest *)request;

- (void)start;

- (void)cancel:(NSError **)error;

@end

WXResourceLoader里面含有一个WXResourceRequest，所以WXResourceRequest也可以看出对网络请求的封装，并且提供了5种不同状态的callback回调函数。

- (void)start
{
    if ([_request.URL isFileURL]) {
        [self _handleFileURL:_request.URL];
        return;
    }

    id<WXResourceRequestHandler> requestHandler = [WXHandlerFactory handlerForProtocol:@protocol(WXResourceRequestHandler)];
    if (requestHandler) {
        [requestHandler sendRequest:_request withDelegate:self];
    } else if ([WXHandlerFactory handlerForProtocol:NSProtocolFromString(@"WXNetworkProtocol")]){
        // deprecated logic
        [self _handleDEPRECATEDNetworkHandler];
    } else {
        WXLogError(@"No resource request handler found!");
    }
}

在调用了WXResourceLoader的start方法以后，会先判断是不是本地的url，如果是本地的文件，那么就直接开始加载。

- (void)_handleFileURL:(NSURL *)url
{
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, ), ^{
        NSData *fileData = [[NSFileManager defaultManager] contentsAtPath:[url path]];
        if (self.onFinished) {
            self.onFinished([[WXResourceResponse alloc]initWithURL:url statusCode: HTTPVersion:@"1.1" headerFields:nil], fileData);
        }
    });
}

本地文件就直接回调onFinished函数。

如果不是本地的文件，就开始发起网络请求，请求服务器端的js文件。

- (void)sendRequest:(WXResourceRequest *)request withDelegate:(id<WXResourceRequestDelegate>)delegate
{
    if (!_session) {
        NSURLSessionConfiguration *urlSessionConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
        if ([WXAppConfiguration customizeProtocolClasses].count > ) {
            NSArray *defaultProtocols = urlSessionConfig.protocolClasses;
            urlSessionConfig.protocolClasses = [[WXAppConfiguration customizeProtocolClasses] arrayByAddingObjectsFromArray:defaultProtocols];
        }
        _session = [NSURLSession sessionWithConfiguration:urlSessionConfig
                                                 delegate:self
                                            delegateQueue:[NSOperationQueue mainQueue]];
        _delegates = [WXThreadSafeMutableDictionary new];
    }

    NSURLSessionDataTask *task = [_session dataTaskWithRequest:request];
    request.taskIdentifier = task;
    [_delegates setObject:delegate forKey:task];
    [task resume];
}

这里的网络请求就是普通的正常NSURLSession网络请求。如果成功，最终都会执行onFinished的回调函数。

    _mainBundleLoader.onFinished = ^(WXResourceResponse *response, NSData *data) {
        __strong typeof(weakSelf) strongSelf = weakSelf;
        NSError *error = nil;
        if ([response isKindOfClass:[NSHTTPURLResponse class]] && ((NSHTTPURLResponse *)response).statusCode != ) {
            error = [NSError errorWithDomain:WX_ERROR_DOMAIN
                                        code:((NSHTTPURLResponse *)response).statusCode
                                    userInfo:@{@"message":@"status code error."}];
            if (strongSelf.onFailed) {
                strongSelf.onFailed(error);
            }
        }

        if (strongSelf.onJSDownloadedFinish) {
            strongSelf.onJSDownloadedFinish(response, request, data, error);
        }

        if (error) {
            WXJSExceptionInfo * jsExceptionInfo = [[WXJSExceptionInfo alloc] initWithInstanceId:@"" bundleUrl:[request.URL absoluteString] errorCode:[NSString stringWithFormat:@"%d", WX_KEY_EXCEPTION_JS_DOWNLOAD] functionName:@"_renderWithRequest:options:data:" exception:[error localizedDescription]  userInfo:nil];
            [WXExceptionUtils commitCriticalExceptionRT:jsExceptionInfo];
            return;
        }

        if (!data) {
            NSString *errorMessage = [NSString stringWithFormat:@"Request to %@ With no data return", request.URL];
            WX_MONITOR_FAIL_ON_PAGE(WXMTJSDownload, WX_ERR_JSBUNDLE_DOWNLOAD, errorMessage, strongSelf.pageName);

            WXJSExceptionInfo * jsExceptionInfo = [[WXJSExceptionInfo alloc] initWithInstanceId:@"" bundleUrl:[request.URL absoluteString] errorCode:[NSString stringWithFormat:@"%d", WX_KEY_EXCEPTION_JS_DOWNLOAD] functionName:@"_renderWithRequest:options:data:" exception:@"no data return"  userInfo:nil];
            [WXExceptionUtils commitCriticalExceptionRT:jsExceptionInfo];

            if (strongSelf.onFailed) {
                strongSelf.onFailed(error);
            }
            return;
        }

        NSString *jsBundleString = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
        NSLog(@"下载下来的 jsBundleString = %@",jsBundleString);
        if (!jsBundleString) {
            WX_MONITOR_FAIL_ON_PAGE(WXMTJSDownload, WX_ERR_JSBUNDLE_STRING_CONVERT, @"data converting to string failed.", strongSelf.pageName)
            return;
        }
        if (!strongSelf.userInfo) {
            strongSelf.userInfo = [NSMutableDictionary new];
        }
        strongSelf.userInfo[@"jsMainBundleStringContentLength"] = @([jsBundleString length]);
        strongSelf.userInfo[@"jsMainBundleStringContentMd5"] = [WXUtility md5:jsBundleString];

        WX_MONITOR_SUCCESS_ON_PAGE(WXMTJSDownload, strongSelf.pageName);
        WX_MONITOR_INSTANCE_PERF_END(WXPTJSDownload, strongSelf);

        [strongSelf _renderWithMainBundleString:jsBundleString];
        [WXTracingManager setBundleJSType:jsBundleString instanceId:weakSelf.instanceId];
    };

在onFinished的回调中，有几种错误判断，例如status code error、no data return、data converting to string failed等。

如果一切正常，那么在onFinished的回调中其实就是拿到jsBundleString，并执行渲染操作。

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

    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];
        }
    }

    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
    //生成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
    // 再次注册默认的模块modules、组件components、handlers，以确保在创建instance之前它们都被注册了
    [WXSDKEngine registerDefaults];
     [[NSNotificationCenter defaultCenter] postNotificationName:WX_SDKINSTANCE_WILL_RENDER object:self];

    [self _handleConfigCenter];
    _needDestroy = YES;
    [WXTracingManager startTracingWithInstanceId:self.instanceId ref:nil className:nil name:WXTExecJS phase:WXTracingBegin functionName:@"renderWithMainBundleString" options:@{@"threadName":WXTMainThread}];
    // 开始createInstance
    [[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);
}

这里WXSDKEngine还会重新再次注册一遍模块modules、组件components、handlers，以确保在创建instance之前它们都被注册了。

- (void)createInstance:(NSString *)instance
              template:(NSString *)temp
               options:(NSDictionary *)options
                  data:(id)data
{
    if (!instance || !temp) return;
    if (![self.instanceIdStack containsObject:instance]) {
        if ([options[@"RENDER_IN_ORDER"] boolValue]) {
            [self.instanceIdStack addObject:instance];
        } else {
            [self.instanceIdStack insertObject:instance atIndex:];
        }
    }
    __weak typeof(self) weakSelf = self;
    WXPerformBlockOnBridgeThread(^(){
        [WXTracingManager startTracingWithInstanceId:instance ref:nil className:nil name:WXTExecJS phase:WXTracingBegin functionName:@"createInstance" options:@{@"threadName":WXTJSBridgeThread}];
[weakSelf.bridgeCtx createInstance:instance
                                  template:temp
                                   options:options
                                      data:data];
        [WXTracingManager startTracingWithInstanceId:instance ref:nil className:nil name:WXTExecJS phase:WXTracingEnd functionName:@"createInstance" options:@{@"threadName":WXTJSBridgeThread}];

    });
}

然后调用WXBridgeContext的createInstance:template:options:data:方法：

- (void)createInstance:(NSString *)instance
              template:(NSString *)temp
               options:(NSDictionary *)options
                  data:(id)data
{
    WXAssertBridgeThread();
    WXAssertParam(instance);

    if (![self.insStack containsObject:instance]) {
        if ([options[@"RENDER_IN_ORDER"] boolValue]) {
            [self.insStack addObject:instance];
        } else {
            [self.insStack insertObject:instance atIndex:];
        }
    }

    //create a sendQueue bind to the current instance
    NSMutableArray *sendQueue = [NSMutableArray array];
    [self.sendQueue setValue:sendQueue forKey:instance];

    NSArray *args = nil;
    if (data){
        args = @[instance, temp, options ?: @{}, data];
    } else {
        args = @[instance, temp, options ?: @{}];
    }
    WX_MONITOR_INSTANCE_PERF_START(WXFirstScreenJSFExecuteTime, [WXSDKManager instanceForID:instance]);
    WX_MONITOR_INSTANCE_PERF_START(WXPTJSCreateInstance, [WXSDKManager instanceForID:instance]);
[self callJSMethod:@"createInstance" args:args];
    WX_MONITOR_INSTANCE_PERF_END(WXPTJSCreateInstance, [WXSDKManager instanceForID:instance]);
}

最终还是WXJSCoreBridge里面的JSContext调用：

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

调用JS的"createInstance"方法。从此处开始，就开始和JSFramework进行相互调用了。下面我们看看整个过程的流程图：

下面我们通过一个示例来说明一下上面的过程。 首先我们在Weex中编写如下代码：

<template>
    <div class="container">
        <image src="https://gw.alicdn.com/tfs/TB1yopEdgoQMeJjy1XaXXcSsFXa-640-302.png" class="pic" @click="picClick"></image>
        <text class="text">{{title}}</text>
    </div>
</template>

<style>
.container {
  align-items: center;
}
.pic {
  margin-top: 100px;
  width: 424px;
  height: 200px;
}
.text {
  margin-top: 40px;
  font-size: 40px;
  color: black;
}
</style>

<script>
module.exports = {
  data: {
    title: 'Hello World',
    toggle: false
  },
  ready: function () {
    console.log('this.title == ' + this.title)
    this.title = 'hello Weex'
    console.log('this.title == ' + this.title)
  },
  methods: {
    picClick: function () {
      this.toggle = !this.toggle
      if (this.toggle) {
        this.title = '图片被点击'
      } else {
        this.title = 'Hello Weex'
      }
    }
  }
}
</script>

运行效果大致如下：

上面的vue文件，经过Weex编译以后，就变成了index.js，里面的代码如下：

// { "framework": "Vue"} 

/******/ (function(modules) { // webpackBootstrap
/******/     // The module cache
/******/     var installedModules = {};
/******/
/******/     // The require function
/******/     function __webpack_require__(moduleId) {
/******/
/******/         // Check if module is in cache
/******/         if(installedModules[moduleId]) {
/******/             return installedModules[moduleId].exports;
/******/         }
/******/         // Create a new module (and put it into the cache)
/******/         var module = installedModules[moduleId] = {
/******/             i: moduleId,
/******/             l: false,
/******/             exports: {}
/******/         };
/******/
/******/         // Execute the module function
/******/         modules[moduleId].call(module.exports, module, module.exports, __webpack_require__);
/******/
/******/         // Flag the module as loaded
/******/         module.l = true;
/******/
/******/         // Return the exports of the module
/******/         return module.exports;
/******/     }
/******/
/******/
/******/     // expose the modules object (__webpack_modules__)
/******/     __webpack_require__.m = modules;
/******/
/******/     // expose the module cache
/******/     __webpack_require__.c = installedModules;
/******/
/******/     // define getter function for harmony exports
/******/     __webpack_require__.d = function(exports, name, getter) {
/******/         if(!__webpack_require__.o(exports, name)) {
/******/             Object.defineProperty(exports, name, {
/******/                 configurable: false,
/******/                 enumerable: true,
/******/                 get: getter
/******/             });
/******/         }
/******/     };
/******/
/******/     // getDefaultExport function for compatibility with non-harmony modules
/******/     __webpack_require__.n = function(module) {
/******/         var getter = module && module.__esModule ?
/******/             function getDefault() { return module['default']; } :
/******/             function getModuleExports() { return module; };
/******/         __webpack_require__.d(getter, 'a', getter);
/******/         return getter;
/******/     };
/******/
/******/     // Object.prototype.hasOwnProperty.call
/******/     __webpack_require__.o = function(object, property) { return Object.prototype.hasOwnProperty.call(object, property); };
/******/
/******/     // __webpack_public_path__
/******/     __webpack_require__.p = "";
/******/
/******/     // Load entry module and return exports
/******/     return __webpack_require__(__webpack_require__.s = 2);
/******/ })
/************************************************************************/
/******/ ([
/* 0 */,
/* 1 */,
/* 2 */
/***/ (function(module, exports, __webpack_require__) {

var __vue_exports__, __vue_options__
var __vue_styles__ = []

/* styles */
__vue_styles__.push(__webpack_require__(3)
)

/* script */
__vue_exports__ = __webpack_require__(4)

/* template */
var __vue_template__ = __webpack_require__(5)
__vue_options__ = __vue_exports__ = __vue_exports__ || {}
if (
  typeof __vue_exports__.default === "object" ||
  typeof __vue_exports__.default === "function"
) {
if (Object.keys(__vue_exports__).some(function (key) { return key !== "default" && key !== "__esModule" })) {console.error("named exports are not supported in *.vue files.")}
__vue_options__ = __vue_exports__ = __vue_exports__.default
}
if (typeof __vue_options__ === "function") {
  __vue_options__ = __vue_options__.options
}
__vue_options__.__file = "/Users/mac/Desktop/GofWeexNoRoute/src/index.vue"
__vue_options__.render = __vue_template__.render
__vue_options__.staticRenderFns = __vue_template__.staticRenderFns
__vue_options__._scopeId = "data-v-11c4006c"
__vue_options__.style = __vue_options__.style || {}
__vue_styles__.forEach(function (module) {
  for (var name in module) {
    __vue_options__.style[name] = module[name]
  }
})
if (typeof __register_static_styles__ === "function") {
  __register_static_styles__(__vue_options__._scopeId, __vue_styles__)
}

module.exports = __vue_exports__
module.exports.el = 'true'
new Vue(module.exports)

/***/ }),
/* 3 */  //第一部分
/***/ (function(module, exports) {

module.exports = {
  "container": {
    "alignItems": "center"
  },
  "pic": {
    "marginTop": "100",
    "width": "424",
    "height": "200"
  },
  "text": {
    "marginTop": "40",
    "fontSize": "40",
    "color": "#000000"
  }
}

/***/ }),
/* 4 */
/***/ (function(module, exports, __webpack_require__) {

"use strict";

//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
//
// 第二部分
module.exports = {
  data: {
    title: 'Hello World',
    toggle: false
  },
  ready: function ready() {
    console.log('this.title == ' + this.title);
    this.title = 'hello Weex';
    console.log('this.title == ' + this.title);
  },
  methods: {
    picClick: function picClick() {
      this.toggle = !this.toggle;
      if (this.toggle) {
        this.title = '图片被点击';
      } else {
        this.title = 'Hello Weex';
      }
    }
  }
};

/***/ }),
/* 5 */
/***/ (function(module, exports) {
// 第三部分
module.exports={render:function (){var _vm=this;var _h=_vm.$createElement;var _c=_vm._self._c||_h;
  return _c('div', {
    staticClass: ["container"]
  }, [_c('image', {
    staticClass: ["pic"],
    attrs: {
      "src": "https://gw.alicdn.com/tfs/TB1yopEdgoQMeJjy1XaXXcSsFXa-640-302.png"
    },
    on: {
      "click": _vm.picClick
    }
  }), _c('text', {
    staticClass: ["text"]
  }, [_vm._v(_vm._s(_vm.title))])])
},staticRenderFns: []}
module.exports.render._withStripped = true

/***/ })
/******/ ]);

看上去一堆代码，实际上也容易看懂。

(function(modules) {
    //......
}

这段代码是自动加的，暂时不管。上述加粗的三部分，分别对应<style>、<script>、<template>。客户端从服务器拿到上述的JS文件之后，就会调用JS的方法createInstance(id, code, config, data)。接下来JSFramework就会调用OC的callNative方法，依次创建视图：

2018-05-11 21:05:23.668059+0800 GofWeexDemo[23922:1755993] <Weex>[debug]WXJSCoreBridge.m:244, callCreateBody...0, {
    attr =     {
        "@styleScope" = "data-v-11c4006c";
    };
    ref = "_root";
    style =     {
        alignItems = center;
    };
    type = div;
},
2018-05-11 21:05:32.116927+0800 GofWeexDemo[23922:1755993] <Weex>[debug]WXJSCoreBridge.m:229, callAddElement...0, _root, {
    attr =     {
        "@styleScope" = "data-v-11c4006c";
        src = "https://gw.alicdn.com/tfs/TB1yopEdgoQMeJjy1XaXXcSsFXa-640-302.png";
    };
    event =     (
        click
    );
    ref = 9;
    style =     {
        height = 200;
        marginTop = 100;
        width = 424;
    };
    type = image;
}, -1
2018-05-11 21:05:32.125669+0800 GofWeexDemo[23922:1755993] <Weex>[debug]WXJSCoreBridge.m:229, callAddElement...0, _root, {
    attr =     {
        "@styleScope" = "data-v-11c4006c";
    };
    ref = 11;
    style =     {
        color = "#000000";
        fontSize = 40;
        marginTop = 40;
    };
    type = text;
}, -1
2018-05-11 21:05:32.127222+0800 GofWeexDemo[23922:1755993] <Weex>[debug]WXJSCoreBridge.m:292, callUpdateAttrs...0, 11, {
    value = "Hello World";
}
2018-05-11 21:05:34.759200+0800 GofWeexDemo[23922:1755993] <Weex>[debug]WXJSCoreBridge.m:354, callRCreateFinish...0
{layout: {width: 320, height: 568, top: 0, left: 0}, flexDirection: 'column', alignItems: 'stretch', flex: 0, width: 320, height: 568, left: 0, top: 0, children: [
  {_root:div layout: {width: 320, height: 568, top: 0, left: 0}, flexDirection: 'column', alignItems: 'center', flex: 0, width: 320, height: 568, children: [
    {9:image layout: {width: 180.907, height: 85.3333, top: 42.6667, left: 69.5467}, flexDirection: 'column', alignItems: 'stretch', flex: 0, marginTop: 42.6667, marginStart: nan, marginEnd: nan, width: 180.907, height: 85.3333, },
    {11:text layout: {width: 93, height: 20.5, top: 145.067, left: 113.5}, flexDirection: 'column', alignItems: 'stretch', flex: 0, marginTop: 17.0667, marginStart: nan, marginEnd: nan, },
  ]},
]},

JSFramework在整个过程中扮演的角色是根据输入的JSBundle，不断的输出Json格式的Virtual DOM，然后通过JSCore调用OC原生方法，生成View。