WebViewJavascriptBridge源码探究--看OC和JS交互过程

;(function() {
    if (window.WebViewJavascriptBridge) { return }
    var messagingIframe
    var sendMessageQueue = []
    var receiveMessageQueue = []
    var messageHandlers = {}
    
    var CUSTOM_PROTOCOL_SCHEME = ‘wvjbscheme‘
    var QUEUE_HAS_MESSAGE = ‘__WVJB_QUEUE_MESSAGE__‘
    
    var responseCallbacks = {}
    var uniqueId = 1
    
    function _createQueueReadyIframe(doc) {
        messagingIframe = doc.createElement(‘iframe‘)
        messagingIframe.style.display = ‘none‘
        messagingIframe.src = CUSTOM_PROTOCOL_SCHEME + ‘://‘ + QUEUE_HAS_MESSAGE
        doc.documentElement.appendChild(messagingIframe)
    }

    function init(messageHandler) {
        if (WebViewJavascriptBridge._messageHandler) { throw new Error(‘WebViewJavascriptBridge.init called twice‘) }
        WebViewJavascriptBridge._messageHandler = messageHandler
        var receivedMessages = receiveMessageQueue
        receiveMessageQueue = null
        for (var i=0; i<receivedMessages.length; i++) {
            _dispatchMessageFromObjC(receivedMessages[i])
        }
    }

    function send(data, responseCallback) {
        _doSend({ data:data }, responseCallback)
    }
    
    function registerHandler(handlerName, handler) {
        messageHandlers[handlerName] = handler
    }
    
    function callHandler(handlerName, data, responseCallback) {
        _doSend({ handlerName:handlerName, 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); //将字典放入数组
        //修改iframe标签的src属性，UIWebView监听执行代理方法
        messagingIframe.src = CUSTOM_PROTOCOL_SCHEME + ‘://‘ + QUEUE_HAS_MESSAGE;
    }

    function _fetchQueue() {  //json数组转成json字符串
        var messageQueueString = JSON.stringify(sendMessageQueue)
        sendMessageQueue = []
        return messageQueueString
    }

    function _dispatchMessageFromObjC(messageJSON) {
        setTimeout(function _timeoutDispatchMessageFromObjC() {
            var message = JSON.parse(messageJSON)
            var messageHandler
            
            if (message.responseId) {
                var responseCallback = responseCallbacks[message.responseId]
                if (!responseCallback) { return; }
                responseCallback(message.responseData)
                delete responseCallbacks[message.responseId]
            } else {
                var responseCallback
                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)
                    }
                }
            }
        })
    }
    
    function _handleMessageFromObjC(messageJSON) {
        if (receiveMessageQueue) {
            receiveMessageQueue.push(messageJSON)
        } else {
            _dispatchMessageFromObjC(messageJSON)
        }
    }

    window.WebViewJavascriptBridge = {
        init: init,
        send: send,
        registerHandler: registerHandler,
        callHandler: callHandler,
        _fetchQueue: _fetchQueue,
        _handleMessageFromObjC: _handleMessageFromObjC
    }

    var doc = document
    _createQueueReadyIframe(doc)
    var readyEvent = doc.createEvent(‘Events‘)
    readyEvent.initEvent(‘WebViewJavascriptBridgeReady‘)
    readyEvent.bridge = WebViewJavascriptBridge
    doc.dispatchEvent(readyEvent)
})();

<html>
    <head>
        <meta charset="utf-8"/>
        <style type="text/css">
            html { font-family:Helvetica; color:#222; background:#D5FFFD; border: 5px dashed blue;}
            .rowH3{margin: 0px; text-align: center;}
            .jsBtn{font-size: 18px;}
        </style>
    </head>
    <body>
        <h3 class="rowH3">测试OC和JS互相调用</h3>
        <button class="jsBtn" id="jsBtn">JS调用OC方法</button>
        <div id="logDiv"><!-- 打印日志 --></div>
    </body>
</html>
<script type="text/javascript">
    window.onerror = function(err) {
        printLog(err);
    }
    
    function connectWebViewJavascriptBridge(callback) {
        if (window.WebViewJavascriptBridge) {
            callback(WebViewJavascriptBridge);
        } else {
            document.addEventListener(‘WebViewJavascriptBridgeReady‘, function() {
                callback(WebViewJavascriptBridge);
            }, false);
        }
    }
    
    var uniqueId = 1;
    //日志打印方法
    function printLog(data) {
        var logObj = document.getElementById(‘logDiv‘);
        var el = document.createElement(‘div‘);
        el.className = ‘logLine‘;
        el.innerHTML = uniqueId++ + ‘: ‘ + JSON.stringify(data); //json转字符串
        if (logObj.children.length) { logObj.insertBefore(el, logObj.children[0]) }
        else { logObj.appendChild(el) }
    }
    
    //初始化调用函数connectWebViewJavascriptBridge
    connectWebViewJavascriptBridge(function(bridge) {
        
        bridge.init(function(message, responseCallback) {});  
                                   
        //注册js响应方法，响应OC调用，标识objc_Call_JS_Func
        bridge.registerHandler(‘objc_Call_JS_Func‘, function(data, responseCallback) {
            printLog(data);  //打印oc传过来的参数
        });

        //给标签按钮设置点击事件
        var callbackButton = document.getElementById(‘jsBtn‘);
        callbackButton.onclick = function(e) {
            e.preventDefault();
            //注册标识js_Call_Objc_Func，便于js给IOS发送消息
            bridge.callHandler(‘js_Call_Objc_Func‘, {id: 1, info: ‘hello, iOS, 我从js那边过来！‘},  function(response) { });
        }
    });
    
</script>