js与native交互之JsBridge

接上篇

JsBridge

1.使用方法

1.1,java调用js指定方法,并有回调:

//java端的代码
webView.callHandler("functionInJs", param, new CallBackFunction() {
            @Override
            public void onCallBack(String data) {
                //拿到H5端回调回来的参数
            }
        });
//H5端的代码
bridge.registerHandler("functionInJs", function(data, responseCallback) {
             document.getElementById("show").innerHTML = ("data from Java: = " + data);
             var responseData = "Javascript Says Right back aka!";
             //将参数回调给native端
             responseCallback(responseData);
        });

java调用callHandler()的方法,必须要在H5中registerHandler(),而且方法名一样才能匹配到,
所以执行上可以看成 java—>js—>java。

1.2,js调用java

1,js发送消息给native端,并有回调

因为没有指定要处理的方法,则由java端的DefaultHandler拦截处理

//js代码
window.WebViewJavascriptBridge.send(
                data
                , function(responseData) {
                    //拿到H5端回调回来的参数
                    document.getElementById("show").innerHTML = "repsonseData from java, data = " + responseData
                }
            );
//java代码
//设置默认回调给JS的方法
webView.setDefaultHandler(new DefaultHandler());

public class DefaultHandler implements BridgeHandler {
    String TAG = "DefaultHandler";
    @Override
    public void handler(String data, CallBackFunction function) {
        if (function != null) {
             //将参数回调到H5端
            function.onCallBack("DefaultHandler response data"+ data);
        }
    }
}

js调用window.WebViewJavascriptBridge.send()的方法,会被java的DefaultHandler拦截
所以执行上可以看成 js—>java—>js。

2,js调用java指定方法,并有回调

//js代码
window.WebViewJavascriptBridge.callHandler(
                'submitFromWeb'
                , {'param': '中文测试'}
                , function(responseData) {
                //拿到H5端回调回来的参数
                document.getElementById("show").innerHTML = "send get responseData from java, data = " + responseData
                }
            );
//java代码
webView.registerHandler("submitFromWeb", new BridgeHandler() {
            @Override
            public void handler(String data, CallBackFunction function) {
                ToastUtil.showShort(ActivityDemo7.this,"hadler = submitFromWeb, data from web = " + data);
                //将参数回调到H5端
                function.onCallBack("submitFromWeb exe, response data 中文 from Java");
            }
        });

2.执行流程分析

2.1,java调用js指定方法,并有回调。

在java代码中,首先找到方法的入口,callHandler()。

webView.callHandler("functionInJs", params, new CallBackFunction() {
            @Override
            public void onCallBack(String data) {

            }
        });

进入callHandler()方法,调用了doSend()方法。

public void callHandler(String handlerName, String data, CallBackFunction callBack) {
        doSend(handlerName, data, callBack);
    }

看doSend()代码

/**
     * native主动调用js代码
     * @param handlerName js中的对应方法的名称
     * @param data 要传递的参数
     * @param responseCallback js代码执行后回调到这里的接口
     */
    private void doSend(String handlerName, String data, CallBackFunction responseCallback) {
        Message m = new Message();
        if (!TextUtils.isEmpty(data)) {
            m.setData(data);
        }
        if (responseCallback != null) {
            String callbackStr = String.format(BridgeUtil.CALLBACK_ID_FORMAT, ++uniqueId + (BridgeUtil.UNDERLINE_STR + SystemClock.currentThreadTimeMillis()));
//            doSend()中callbackStr:JAVA_CB_3_998
//            doSend()中callbackStr:JAVA_CB_4_1022
            Log.i("BridgeWebView","doSend()中callbackStr:"+callbackStr);
            responseCallbacks.put(callbackStr, responseCallback);
            m.setCallbackId(callbackStr);
        }
        if (!TextUtils.isEmpty(handlerName)) {
            m.setHandlerName(handlerName);
        }
        queueMessage(m);
    }

这里组装Message对象来保存调用方法的信息,假如存入了回调函数responseCallback ,则生成一个callbackStr 保存到本地的responseCallbacks中,继续进入queueMessage()方法

private void queueMessage(Message m) {
        //假如native调用js代码,则startupMessage为null
        if (startupMessage != null) {
            startupMessage.add(m);
        } else {
            dispatchMessage(m);
        }
    }

假如native调用js代码,则startupMessage为null,所以进入到dispatchMessage()方法中

void dispatchMessage(Message m) {
        String messageJson = m.toJson();
        //escape special characters for json string
        messageJson = messageJson.replaceAll("(\\\\)([^utrn])", "\\\\\\\\$1$2");
        messageJson = messageJson.replaceAll("(?<=[^\\\\])(\")", "\\\\\"");
        String javascriptCommand = String.format(BridgeUtil.JS_HANDLE_MESSAGE_FROM_JAVA, messageJson);
//        dispatchMessage()中javascriptCommand:javascript:WebViewJavascriptBridge._handleMessageFromNative('{\"data\":\"hello\"}');
//        dispatchMessage()中javascriptCommand:javascript:WebViewJavascriptBridge._handleMessageFromNative('{\"callbackId\":\"JAVA_CB_1_877\",\"data\":\"{\\\"location\\\":{\\\"address\\\":\\\"SDU\\\"},\\\"name\\\":\\\"大头鬼\\\"}\",\"handlerName\":\"functionInJs\"}');
        Log.i("BridgeWebView","dispatchMessage()中javascriptCommand:"+javascriptCommand);
        if (Thread.currentThread() == Looper.getMainLooper().getThread()) {
            this.loadUrl(javascriptCommand);
        }
    }

这段代码就是native调用js代码的关键,方法中先从message对象中解析json数据将信息解析,拼接出类似

javascript:WebViewJavascriptBridge._handleMessageFromNative('{\"callbackId\":\"JAVA_CB_1_877\",\"data\":\"{\\\"location\\\":{\\\"address\\\":\\\"SDU\\\"},\\\"name\\\":\\\"大头鬼\\\"}\",\"handlerName\":\"functionInJs\"}

的代码,再通过

if (Thread.currentThread() == Looper.getMainLooper().getThread()) {
            this.loadUrl(javascriptCommand);
        }

在主线程中webView.loadUrl(),所以其实java调用js的核心还是webView.loadUrl()这个方法,但是JsBridge库对其进行了封装,这样java就不能调用js中的任意代码(本来webView.loadUrl()这个方法只要传入拼接对的js代码,就能调用该js代码)。
追踪到js的WebViewJavascriptBridge._handleMessageFromNative代码

function _handleMessageFromNative(messageJSON) {
        console.log(messageJSON);
        if (receiveMessageQueue && receiveMessageQueue.length > 0) {
            receiveMessageQueue.push(messageJSON);
        } else {
            _dispatchMessageFromNative(messageJSON);
        }
    }

这里还没搞懂receiveMessageQueue 的作用是什么,只知道调用了_dispatchMessageFromNative()方法,所以继续进入方法

//按照messageJson进行事件的调用,假如有callback,则调用完之后callback
    function _dispatchMessageFromNative(messageJSON) {
        setTimeout(function() {
            //解析出callbackId(假如存在回调)和参数,
            var message = JSON.parse(messageJSON);
            var responseCallback;
            //java call finished, now need to call js callback function
            //假如存在responseId,则回调完成时去除callId
            if (message.responseId) {
                responseCallback = responseCallbacks[message.responseId];
                if (!responseCallback) {
                    return;
                }
                responseCallback(message.responseData);
                delete responseCallbacks[message.responseId];
            } else {
                //直接发送
                if (message.callbackId) {
                    var callbackResponseId = message.callbackId;
                    responseCallback = function(responseData) {
                        //js回调给java
                        _doSend({
                            responseId: callbackResponseId,
                            responseData: responseData
                        });
                    };
                }
                var handler = WebViewJavascriptBridge._messageHandler;
                if (message.handlerName) {
                    handler = messageHandlers[message.handlerName];
                }
                //查找指定handler
                try {
                    handler(message.data, responseCallback);
                } catch (exception) {
                    if (typeof console != 'undefined') {
                        console.log("WebViewJavascriptBridge: WARNING: javascript handler threw.", message, exception);
                    }
                }
            }
        });
    }

这段代码中,因为是java主动调用js,所以message.responseId为null,直接走else,先组装回调函数responseCallBack()

if (message.callbackId) {
                    var callbackResponseId = message.callbackId;
                    responseCallback = function(responseData) {
                        //js回调给java
                        _doSend({
                            responseId: callbackResponseId,
                            responseData: responseData
                        });
                    };
                }

接着根据handler = messageHandlers[message.handlerName];拿到handler

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

最后就是调用方法,追踪到注册的方法

connectWebViewJavascriptBridge(function(bridge) {
            ......
            //为js注册Handler,
            bridge.registerHandler("functionInJs", function(data, responseCallback) {
                document.getElementById("show").innerHTML = ("data from Java: = " + data);
                var responseData = "Javascript Says Right back aka!";
                responseCallback(responseData);
            });
        })

最后调用了responseCallback(responseData),responseCallback()在上面已经组装成功,就是调用了_doSend()这个方法

//sendMessage add message, 触发native处理 sendMessage
//将数据返回到native,回调到native时就是调用这个方法
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;
    }

这里涉及到一些前端的知识,利用iframe.src的变化,触发了BridgeWebViewClient的shouldOverrideUrlLoading将数据返回到native端,这样就实现了js回调到native了。

所以总体上流程是:

Paste_Image.png

3,js调用java指定方法,并有回调

找到js代码的入口,window.WebViewJavascriptBridge.callHandler(...)

//function的responseData是回调的值
            //js调用特定的java方法
            window.WebViewJavascriptBridge.callHandler(
                'submitFromWeb'
                , {'param': '中文测试'}
                , function(responseData) {
                    document.getElementById("show").innerHTML = "send get responseData from java, data = " + responseData
                }
            );

进入callHandler()方法,也是调用了_doSend()方法,将数据传递到native

function callHandler(handlerName, data, responseCallback) {
        _doSend({
            handlerName: handlerName,
            data: data
        }, responseCallback);
    }

与上面js调用java流程中的_doSend()一样,通过改变iframe.src触发native的shouldOverrideUrlLoading()方法

 @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        try {
            url = URLDecoder.decode(url, "UTF-8");
            Log.i("BridgeWebViewClient","查看触发的schema:"+url);
        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
        }

        if (url.startsWith(BridgeUtil.YY_RETURN_DATA)) { // 如果是返回数据
            webView.handlerReturnData(url);
            return true;
        } else if (url.startsWith(BridgeUtil.YY_OVERRIDE_SCHEMA)) { //
            webView.flushMessageQueue();
            return true;
        } else {
            return super.shouldOverrideUrlLoading(view, url);
        }
    }

接着走的是webView.flushMessageQueue()这个方法

void flushMessageQueue() {
        if (Thread.currentThread() == Looper.getMainLooper().getThread()) {
            loadUrl(BridgeUtil.JS_FETCH_QUEUE_FROM_JAVA, new CallBackFunction() {

                @Override
                public void onCallBack(String data) {
                    // deserializeMessage
                    List<Message> list = null;
                    try {
                        list = Message.toArrayList(data);
                    } catch (Exception e) {
                        e.printStackTrace();
                        return;
                    }
                    if (list == null || list.size() == 0) {
                        return;
                    }
                    for (int i = 0; i < list.size(); i++) {
                        Message m = list.get(i);
                        String responseId = m.getResponseId();
                        // 是否是response
                        if (!TextUtils.isEmpty(responseId)) {
                            CallBackFunction function = responseCallbacks.get(responseId);
                            String responseData = m.getResponseData();
                            function.onCallBack(responseData);
                            responseCallbacks.remove(responseId);
                        } else {
                            CallBackFunction responseFunction = null;
                            // if had callbackId
                            final String callbackId = m.getCallbackId();
                            if (!TextUtils.isEmpty(callbackId)) {
                                responseFunction = new CallBackFunction() {
                                    @Override
                                    public void onCallBack(String data) {
                                        Message responseMsg = new Message();
                                        responseMsg.setResponseId(callbackId);
                                        responseMsg.setResponseData(data);
                                        queueMessage(responseMsg);
                                    }
                                };
                            } else {
                                responseFunction = new CallBackFunction() {
                                    @Override
                                    public void onCallBack(String data) {
                                        // do nothing
                                    }
                                };
                            }
                            BridgeHandler handler;
                            if (!TextUtils.isEmpty(m.getHandlerName())) {
                                handler = messageHandlers.get(m.getHandlerName());
                            } else {
                                handler = defaultHandler;
                            }
                            if (handler != null) {
                                handler.handler(m.getData(), responseFunction);
                            }
                        }
                    }
                }
            });
        }
    }

这个方法是在BridgeWebView中定义的,做的是在主线程中调用loadUrl(javascript:WebViewJavascriptBridge._fetchQueue(), new CallBackFunction());这个方法。
所以,追踪到js中的_fetchQueue()中

// 提供给native调用,该函数作用:获取sendMessageQueue返回给native,由于android不能直接获取返回的内容,所以使用url shouldOverrideUrlLoading 的方式返回内容
    function _fetchQueue() {
        var messageQueueString = JSON.stringify(sendMessageQueue);
        sendMessageQueue = [];
        //android can't read directly the return data, so we can reload iframe src to communicate with java
        messagingIframe.src = CUSTOM_PROTOCOL_SCHEME + '://return/_fetchQueue/' + encodeURIComponent(messageQueueString);
    }

这里将js传递的参数拼接入Url中,传递到native,而相应的shouldOverrideUrlLoading 中调用handlerReturnData()这个方法

/**
     * 处理返回的数据
     *
     * @param url
     */
    void handlerReturnData(String url) {
        String functionName = BridgeUtil.getFunctionFromReturnUrl(url);
        CallBackFunction f = responseCallbacks.get(functionName);
        String data = BridgeUtil.getDataFromReturnUrl(url);
        if (f != null) {
            f.onCallBack(data);
            responseCallbacks.remove(functionName);
            return;
        }
    }

这里就是调用native本地方法

if (f != null) {
            f.onCallBack(data);
}

所以总体上流程是

Paste_Image.png

留意整个流程,js的第一次_doSend()只不过是通知native调用javascript:WebViewJavascriptBridge._fetchQueue();来取消息,包括要调用的方法,参数,回调的id。所以其实真正调用native方法的是js层的_fetchQueue()。

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