WebViewJavascriptBridge源码分析

最近抽时间看了一遍WebViewJavascriptBridge这个开源框架，把看到的内容记录下来

源码地址：https://github.com/marcuswestin/WebViewJavascriptBridge

1、对外接口

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) { ... })

三类API接口用于OC与JS之间交互：初始化接口；发送消息接口，并且可以添加发送消息完成的回调函数；事件注册和调用接口，需要先在一端注册事件，另一端可以根据事件名称调用函数

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

2、类结构图

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；

3、源码分析

3.1 消息发送JS－》Native

[bridge send:(id)data]

[bridge send:(id)data responseCallback:(WVJBResponseCallback)responseCallback]

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

function _doSend (message , responseCallback )  {
        if  (responseCallback )  {
                var callbackId  =  ' cb_ ' + (uniqueId ++ ) + ' _ ' + new  Date ( ) . getTime ( )
               responseCallbacks [callbackId ]  = responseCallback
              message [ ' callbackId ' ]  = callbackId
      }
     sendMessageQueue .push (message )
     messagingIframe .src  = CUSTOM_PROTOCOL_SCHEME  +  ' :// '  + QUEUE_HAS_MESSAGE
}

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 ([ _base isCorrectProcotocolScheme:url]) {
        if ([ _base isCorrectHost:url]) {
            NSString *messageQueueString = [ self _evaluateJavascript:[ _base webViewJavascriptFetchQueyCommand]];
            [ _base flushMessageQueue:messageQueueString];
        } else {
            [ _base logUnkownMessage:url];
        }
        return NO;
    } else if (strongDelegate && [strongDelegate respondsToSelector: @selector(webView:shouldStartLoadWithRequest:navigationType:)]) {
        return [strongDelegate webView:webView shouldStartLoadWithRequest:request navigationType:navigationType];
    } else {
        return YES;
    }

}

重点部分：执行注入 _evaluateJavascript，

OC

-( 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:[ _base webViewJavascriptFetchQueyCommand]];这句代码获得从JS侧拿到的数据内容，然后调用[ _base flushMessageQueue: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: %@", [messages class], messages);
        return;
    }
    for ( WVJBMessage* message in messages) {
        if (![message isKindOfClass:[ WVJBMessage class]]) {
            NSLog( @"WebViewJavascriptBridge: WARNING: Invalid %@ received: %@", [message class], message);
            continue;
        }
        [ self _log: @"RCVD" json:message];
       
        NSString* responseId = message[ @"responseId"];
        if (responseId) {
            WVJBResponseCallback responseCallback = _responseCallbacks[responseId];
            responseCallback(message[ @"responseData"]);
            [ self. responseCallbacks removeObjectForKey:responseId];
        } else {
            WVJBResponseCallback responseCallback = NULL;
            NSString* callbackId = message[ @"callbackId"];
            if (callbackId) {
                responseCallback = ^( id responseData) {
                    if (responseData == nil) {
                        responseData = [ NSNull null];
                    }
                   
                    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. startupMessageQueue addObject: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 = [ NSString stringWithFormat: @"WebViewJavascriptBridge._handleMessageFromObjC('%@');", messageJSON];
    if ([[ NSThread currentThread] 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

这个是整个框架中JS侧重要的函数，用于处理从OC侧返回的消息

function _dispatchMessageFromObjC (messageJSON )  {
        setTimeout ( function _timeoutDispatchMessageFromObjC ( )  {
            var message  = JSON . parse (messageJSON )
            var messageHandler
            var responseCallback

            if  (message .responseId )  {
                responseCallback  = responseCallbacks [message .responseId ]
                if  ( !responseCallback )  {  return ;  }
                responseCallback (message .responseData )
                delete responseCallbacks [message .responseId ]
            }  else  {
                if  (message .callbackId )  {
                    var callbackResponseId  = message .callbackId
                    responseCallback  =  function (responseData )  {
                        _doSend ( { responseId :callbackResponseId , responseData :responseData  } )
                    }
                }

                var handler  = WebViewJavascriptBridge ._messageHandler
                if  (message .handlerName )  {
                    handler  = messageHandlers [message .handlerName ]
                }

                try  {
                    handler (message .data , responseCallback )
                }  catch (exception )  {
                    if  ( typeof console  !=  ' undefined ' )  {
                        console . log ( " WebViewJavascriptBridge: WARNING: javascript handler threw. " , message , exception )
                    }
                }
            }
        } )
    }

执行JS侧本地回调函数

3.2 消息发送 OC--》JS

bridge.send("Hi there!")

bridge.send({ Foo:"Bar" })

bridge.send(data, function responseCallback(responseData) { ... })

调用

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

执行 _queueMessage

3.3 OC注册事件和JS调用

OC侧注册

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

    _base. messageHandlers[handlerName] = [handler copy];

}

JS调用

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

3.4 JS注册事件和OC调用

JS注册

function registerHandler(handlerName, handler) {

     messageHandlers[handlerName] = handler

}

本地记录

OC调用

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

}

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

}

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

4 、总结

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