WebViewJavascriptBridge源码分析

初始化OC	初始化JS
[WebViewJavascriptBridge bridgeForWebView:(UIWebView/WebView*)webview handler:(WVJBHandler)handler]   [WebViewJavascriptBridge bridgeForWebView:(UIWebView/WebView*)webview webViewDelegate:(UIWebViewDelegate*)webViewDelegate handler:(WVJBHandler)handler]	document.addEventListener(‘WebViewJavascriptBridgeReady‘, function onBridgeReady(event) { ... }, false)   bridge.init(function messageHandler(data, response) { ... })
OC发送消息to JS	JS发送消息to OC
[bridge send:(id)data] [bridge send:(id)data responseCallback:(WVJBResponseCallback)responseCallback]	bridge.send("Hi there!") bridge.send({ Foo:"Bar" }) bridge.send(data, function responseCallback(responseData) { ... })
OC注册事件（先）	JS调用事件（后）
[bridge registerHandler:(NSString*)handlerName handler:(WVJBHandler)handler]	WebViewJavascriptBridge.callHandler("handlerName")
OC调用事件（后）	JS注册事件（先）
[bridge callHandler:(NSString*)handlerName data:(id)data] [bridge callHandler:(NSString*)handlerName data:(id)data responseCallback:(WVJBResponseCallback)callback]	bridge.registerHandler("handlerName", function(responseData) { ... })

除了上述提到的外部方法：还有两个方法十分重要，JS部分最重要的内部方法： _handleMessageFromObjC；OC部分重要的内部方法：flushMessageQueue

WebViewJavascriptBridge目前既支持原有的UIWebView，也支持iOS8+之后新的WKWebView，使用时可以二选其一；

WebViewjavascriptBridgeBase是通用类，用于处理从Native到JS的消息注入，消息队列处理和分发，JSON数据的序列化和反序列化，LOG输出；

这两个函数最后都是调用_doSend({ data:data }, responseCallback)

首先生成callbackId，由不断加1的唯一需要和时间戳构成，如果有responseCallback函数，使用callbackId作为索引，存入responseCallbacks对象，等到从OC侧返回的信息中对应的callbackId与当前responseCallbacks中callbackId相同时，调用回调函数responseCallback；sendMessageQueue是个消息数组，每次的新消息放入其中，messagingIframe是iframe对象，当设置src产生一次请求，在OC端的

(BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType 会拦截请求内容

代码：

- (BOOL)webView:(UIWebView *)webView shouldStartLoadWithRequest:(NSURLRequest *)request navigationType:(UIWebViewNavigationType)navigationType {
    if (webView != _webView) { return YES; }
    NSURL *url = [request URL];
    __strong WVJB_WEBVIEW_DELEGATE_TYPE* strongDelegate = _webViewDelegate;
    if ([_baseisCorrectProcotocolScheme:url]) {
        if ([_baseisCorrectHost:url]) {
            NSString *messageQueueString = [self_evaluateJavascript:[_basewebViewJavascriptFetchQueyCommand]];
            [_base flushMessageQueue:messageQueueString];
        } else {
            [_base logUnkownMessage:url];
        }
        return NO;
    } else if (strongDelegate && [strongDelegate respondsToSelector:@selector(webView:shouldStartLoadWithRequest:navigationType:)]) {
        return [strongDelegate webView:webView shouldStartLoadWithRequest:requestnavigationType:navigationType];
    } else {
        return YES;
    }

}

-(NSString *)webViewJavascriptFetchQueyCommand {
    return @"WebViewJavascriptBridge._fetchQueue();";

}

JS

function _fetchQueue() {

    var messageQueueString = JSON.stringify(sendMessageQueue)

    sendMessageQueue = []

   return messageQueueString

}

这个函数从JS的sendMessageQueue消息队列获取内容返回，这个sendMessageQueue是在之前的_doSend函数中传入的消息内容，也就是NSString *messageQueueString = [self_evaluateJavascript:[_basewebViewJavascriptFetchQueyCommand]];这句代码获得从JS侧拿到的数据内容，然后调用[_baseflushMessageQueue:messageQueueString];对消息分发处理

- (void)flushMessageQueue:(NSString *)messageQueueString{
    id messages = [self_deserializeMessageJSON:messageQueueString];
    if (![messages isKindOfClass:[NSArray class]]) {
        NSLog(@"WebViewJavascriptBridge: WARNING: Invalid %@ received: %@", [messagesclass], messages);
        return;
    }
    for (WVJBMessage* messagein messages) {
        if (![message isKindOfClass:[WVJBMessage class]]) {
            NSLog(@"WebViewJavascriptBridge: WARNING: Invalid %@ received: %@", [messageclass], message);
            continue;
        }
        [self _log:@"RCVD" json:message];
       
        NSString* responseId = message[@"responseId"];
        if (responseId) {
            WVJBResponseCallback responseCallback =_responseCallbacks[responseId];
            responseCallback(message[@"responseData"]);
            [self.responseCallbacksremoveObjectForKey:responseId];
        } else {
            WVJBResponseCallback responseCallback =NULL;
            NSString* callbackId = message[@"callbackId"];
            if (callbackId) {
                responseCallback = ^(id responseData) {
                    if (responseData == nil) {
                        responseData = [NSNullnull];
                    }
                   
                    WVJBMessage* msg = @{@"responseId":callbackId, @"responseData":responseData };
                    [self _queueMessage:msg];
                };
            } else {
                responseCallback = ^(id ignoreResponseData) {
                    // Do nothing
                };
            }
           
            WVJBHandler handler;
            if (message[@"handlerName"]) {
                handler = self.messageHandlers[message[@"handlerName"]];
            } else {
                handler = self.messageHandler;
            }
           
            if (!handler) {
                [NSException raise:@"WVJBNoHandlerException" format:@"No handler for message from JS: %@", message];
            }
           
            handler(message[@"data"], responseCallback);
        }
    }

}

这个是整个框架中OC侧重要的函数，但是目前首先分析消息发送JS－》Native涉及到的部分内容，返回的消息包含callbackId，数据拼接后调用[self_queueMessage:msg];发送回JS侧的数据改为responseId为关键字key，具体如下：

- (void)_queueMessage:(WVJBMessage*)message {
    if (self.startupMessageQueue) {
        [self.startupMessageQueueaddObject:message];
    } else {
        [self _dispatchMessage:message];
    }

}

self.startupMessageQueue只有首次启动时有效，之后为nil，所以都是走[self_dispatchMessage:message];

- (void)_dispatchMessage:(WVJBMessage*)message {
    NSString *messageJSON = [self_serializeMessage:message];
    [self _log:@"SEND" json:messageJSON];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\\"withString:@"\\\\"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\""withString:@"\\\""];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\‘"withString:@"\\\‘"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\n"withString:@"\\n"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\r"withString:@"\\r"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\f"withString:@"\\f"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\u2028"withString:@"\\u2028"];
    messageJSON = [messageJSON stringByReplacingOccurrencesOfString:@"\u2029"withString:@"\\u2029"];
   
    NSString* javascriptCommand = [NSStringstringWithFormat:@"WebViewJavascriptBridge._handleMessageFromObjC(‘%@‘);", messageJSON];
    if ([[NSThreadcurrentThread] isMainThread]) {
        [self _evaluateJavascript:javascriptCommand];

    } else {
        dispatch_sync(dispatch_get_main_queue(), ^{
            [self _evaluateJavascript:javascriptCommand];
        });
    }

}

此函数对message特殊字符进行转义处理，然后执行JS注入语句，WebViewJavascriptBridge._handleMessageFromObjC执行到JS侧

调用

    [_base sendData:dataresponseCallback:responseCallback handlerName:nil];

执行 _queueMessage

- (void)registerHandler:(NSString *)handlerName handler:(WVJBHandler)handler {

    _base.messageHandlers[handlerName] = [handlercopy];

}

function callHandler(handlerName, data, responseCallback) {

     _doSend({ handlerName:handlerName, data:data }, responseCallback)

}

加入handlerName和data数据传给OC侧，JS侧记录responseCallback，最后也会走到- (void)flushMessageQueue:(NSString *)messageQueueString函数中，由于既没有callbackId也没有responseId，所以只处理handlerName及相关数据，最后走到 - (void)flushMessageQueue:(NSString *)messageQueueString解析，OC侧执行之前注册的handler并传入data数据

function registerHandler(handlerName, handler) {

     messageHandlers[handlerName] = handler

}

- (void)callHandler:(NSString *)handlerName data:(id)data {
    [self callHandler:handlerName data:dataresponseCallback:nil];

}

- (void)callHandler:(NSString *)handlerName data:(id)data responseCallback:(WVJBResponseCallback)responseCallback {
    [_base sendData:data responseCallback:responseCallbackhandlerName:handlerName];

}

handlerName和data  在 - (void)sendData:(id)data responseCallback:(WVJBResponseCallback)responseCallback handlerName:(NSString*)handlerName中处理

1、与其它框架相比，此框架没有采用url拦截解析参数方式，而是多次JS注入参数获取，API接口暴露的操作在底层需要多次OC与JS之间交互完成

2、WKwebview部分没有使用新的delgate方法，而是沿用iframe方式，个人觉得采用新接口可能效率更高

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