本篇文章已授權(quán)微信公眾號(hào) guolin_blog （郭霖）獨(dú)家發(fā)布
在Android開(kāi)發(fā)中龄章，由于Native開(kāi)發(fā)的成本較高，H5頁(yè)面的開(kāi)發(fā)更靈活，修改成本更低，因此前端網(wǎng)頁(yè)JavaScript(下面簡(jiǎn)稱JS)與Java之間的互相調(diào)用越來(lái)越常見(jiàn)惧浴。
JsBridge就是一個(gè)簡(jiǎn)化Android與JS通信的框架，源碼：https://github.com/lzyzsd/JsBridge
我們今天通過(guò)一個(gè)簡(jiǎn)單栗子來(lái)分析下開(kāi)源框架JsBridge的源碼奕剃。栗子的代碼我也放在Github衷旅，有需要的可以seesee：
https://github.com/juexingzhe/Android_JS
栗子很簡(jiǎn)單，隨便輸入信息登陸纵朋，會(huì)加載一個(gè)H5頁(yè)面柿顶，在H5界面點(diǎn)擊按鈕，Java執(zhí)行g(shù)etUserInfo()然后將UserInfo回傳給JS操软，H5頁(yè)面再顯示UserInfo嘁锯。
JS調(diào)用Android基本有下面三種方式
webView.addJavascriptInterface()
WebViewClient.shouldOverrideUrlLoading()
WebChromeClient.onJsAlert()/onJsConfirm()/onJsPrompt() 方法分別回調(diào)攔截JS對(duì)話框alert()、confirm()聂薪、prompt()消息
Android調(diào)用JS
webView.loadUrl();
webView.evaluateJavascript()
常用方法的使用后面栗子中會(huì)用到家乘，更細(xì)節(jié)的介紹各位同學(xué)可以去網(wǎng)上搜搜看看。
1.JsBridge使用
我們先來(lái)看下Java層的代碼
首先引入依賴和倉(cāng)庫(kù)
dependencies {
……
compile 'com.github.lzyzsd:jsbridge:1.0.4'
compile 'com.google.code.gson:gson:2.7'
}
repositories {
jcenter()
maven { url "https://jitpack.io" }
}
準(zhǔn)備工作就是這樣藏澳，下面可以開(kāi)始擼代碼烤低，首先就是點(diǎn)擊按鈕登陸,這個(gè)簡(jiǎn)單：
Intent intent = new Intent(LoginActivity.this, WebActivity.class);
intent.putExtra("email", mEmailView.getText().toString());
startActivity(intent);
布局文件中要使用BridgeWebView:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<com.github.lzyzsd.jsbridge.BridgeWebView
android:id="@+id/web_view"
android:layout_width="match_parent"
android:layout_height="match_parent" />
</LinearLayout>
在跳轉(zhuǎn)后的頁(yè)面,獲取登陸信息并存儲(chǔ)，再通過(guò)loadUrl加載H5頁(yè)面：
Intent intent = this.getIntent();
String email = intent.getStringExtra("email");
mUserInfo = new UserInfo(email);
mBridgeWebView = (BridgeWebView) findViewById(R.id.web_view);
mBridgeWebView.setDefaultHandler(new DefaultHandler());
mBridgeWebView.loadUrl("file:///android_asset/getuserinfo.html");
registerHandler();
主要是要注冊(cè)Handler笆载，供JS調(diào)用,
getUserInfo就是注冊(cè)供JS調(diào)用的Handler的id
data是JS傳過(guò)來(lái)的參數(shù)
CallBackFunction 函數(shù)中需要把JS需要的response返回給JS
private void registerHandler() {
mBridgeWebView.registerHandler("getUserInfo", new BridgeHandler() {
@Override
public void handler(String data, CallBackFunction function) {
Log.i(TAG, "handler = getUserInfo, data from web = " + data);
function.onCallBack(new Gson().toJson(mUserInfo));
}
});
}
Java層的代碼就這么簡(jiǎn)單，下面看下JS層工作：
首先需要一個(gè)js文件涯呻，我們寫一個(gè)getuserinfo.html文件放在assets目錄下凉驻，文件內(nèi)容,不建議把js代碼直接放在html文件中，我為了方便直接就寫在這了复罐。代碼放了兩個(gè)段落涝登，一個(gè)類似于TextView用來(lái)顯示用戶信息，一個(gè)Button效诅。點(diǎn)擊按鈕會(huì)調(diào)用callHandler胀滚，三個(gè)參數(shù)和Java層一一對(duì)應(yīng)趟济，在Java層返回的時(shí)候，會(huì)調(diào)用function(responseData)函數(shù)咽笼，顯示用于信息顷编。
<html>
<head>
<meta content="text/html; charset=utf-8" http-equiv="content-type">
<title>
js調(diào)用java
</title>
</head>
<body>
<p>
<xmp id="show">
</xmp>
</p>
<div align="center">
<p>
<input type="button" id="enter" value="獲取用戶信息" onclick="getUserInfo();"
/>
</p>
</div>
</body>
<script>
function getUserInfo(){
window.WebViewJavascriptBridge.callHandler(
'getUserInfo',
{'info': 'I am JS, want to get UserInfo from Java'},
function(responseData) {
document.getElementById("show").innerHTML = "repsonseData from java,\ndata = " + responseData;
}
)
}
</script>
</html>
使用基本就是這樣了，可以看出來(lái)JsBridge通過(guò)封裝剑刑，JS和Java之間的通信只需要實(shí)現(xiàn)兩個(gè)步驟媳纬，使用起來(lái)很方便。
我們來(lái)看下源碼是怎么個(gè)玩法施掏，先來(lái)個(gè)華麗麗的分割線
2.JsBridge源碼分析
分析之前我把JS調(diào)用Java畫了個(gè)簡(jiǎn)易交互圖钮惠，Java調(diào)用JS的過(guò)程類似：
是不是感覺(jué)反而更復(fù)雜了？七芭？素挽？其實(shí)只要捉住主要的三點(diǎn)，JsBridge就原形畢露：
1.Android調(diào)用JS是通過(guò)loadUrl(url),url中可以拼接要傳給JS的對(duì)象
2.JS調(diào)用Android是通過(guò)shouldOverrideUrlLoading
3.JsBridge將溝通數(shù)據(jù)封裝成Message狸驳，然后放進(jìn)Queue,再將Queue進(jìn)行傳輸
接下來(lái)我們來(lái)一步一步跟蹤上面栗子的調(diào)用過(guò)程：
- JS層點(diǎn)擊按鈕調(diào)用callHandler
handlerName预明，Java和JS要一致，
data是Java層handlerName函數(shù)執(zhí)行的參數(shù)
responseCallback是Java執(zhí)行完handlerName返回時(shí)锌历，JS回調(diào)的接口贮庞，是JS執(zhí)行
onclick="getUserInfo();"
function getUserInfo(){
window.WebViewJavascriptBridge.callHandler(
'getUserInfo',
{'info': 'I am JS, want to get UserInfo from Java'},
function(responseData) {
document.getElementById("show").innerHTML = "repsonseData from java,\ndata = " + responseData;
}
)
}
callHandler會(huì)調(diào)用_doSend
如果JS需要回調(diào)，就將回調(diào)的callbackId放進(jìn)message中究西，Java執(zhí)行完會(huì)傳回callbackId窗慎，這里是cb_1_1495182409011
構(gòu)造完message放進(jìn)隊(duì)列sendMessageQueue
通過(guò)iframe屬性給Java發(fā)送通知消息，消息結(jié)構(gòu)yy://QUEUE_MESSAGE/
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);
messagingIframe.src = CUSTOM_PROTOCOL_SCHEME + '://' + QUEUE_HAS_MESSAGE;
}
- Java收到通知消息
WebView在shouldOverrideUrlLoading攔截到url：yy://QUEUE_MESSAGE/
然后會(huì)執(zhí)行webView.flushMessageQueue()卤材，在主線程執(zhí)行l(wèi)oadUrl通知JS層推送隊(duì)列到Java;
JS_FETCH_QUEUE_FROM_JAVA = "javascript:WebViewJavascriptBridge._fetchQueue();"
調(diào)用JS層的_fetchQueue遮斥，通知JS層發(fā)送隊(duì)列到Java層
在responseCallbacks中注冊(cè)回調(diào)接口，接口id是函數(shù)名_fetchQueue扇丛，在JS推送消息隊(duì)列時(shí)進(jìn)行回調(diào)
void flushMessageQueue() {
if (Thread.currentThread() == Looper.getMainLooper().getThread()) {
loadUrl(BridgeUtil.JS_FETCH_QUEUE_FROM_JAVA, new CallBackFunction() {
@Override
public void onCallBack(String data) {
//
});
}
}
public void loadUrl(String jsUrl, CallBackFunction returnCallback) {
this.loadUrl(jsUrl);
responseCallbacks.put(BridgeUtil.parseFunctionName(jsUrl), returnCallback);
}
- JS 發(fā)送Request Queue
執(zhí)行_fetchQueue
將sendMessageQueue轉(zhuǎn)化成JSON
通過(guò)iframe屬性給Java發(fā)送通知消息术吗，消息結(jié)構(gòu)：yy://return/_fetchQueue/消息隊(duì)列的內(nèi)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);
}
- Java收到調(diào)用通知，進(jìn)行處理并發(fā)送Response Queue到JS
WebView在shouldOverrideUrlLoading會(huì)攔截到url：
yy://return/_fetchQueue/[{"handlerName":"getUserInfo","data":{"info":"I am JS, want to get UserInfo from Java"},"callbackId":"cb_1_1495180503779"}]
執(zhí)行webView.handlerReturnData(url);
根據(jù)函數(shù)名_fetchQueue拿到之前注冊(cè)的回調(diào)函數(shù)CallBackFunction returnCallback
執(zhí)行回調(diào)函數(shù)帆精，并且從注冊(cè)中移除
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;
}
}
接下來(lái)就是對(duì)Request Queue的解析然后找到JS希望調(diào)用Handler并且執(zhí)行较屿，代碼中我寫了注釋，可以直接看：
//回調(diào)接口執(zhí)行onCallBack函數(shù)
//其中data [{"handlerName":"getUserInfo","data":{"info":"I am JS, want to get UserInfo from Java"},"callbackId":"cb_1_1495180503779"}]
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 {
//將JSON數(shù)組轉(zhuǎn)化成Java list
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++) {
//從list中取出Message
Message m = list.get(i);
//在我們的栗子中沒(méi)有responseId卓练，因此到else分支
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
//如果有callbackId就說(shuō)明JS需要回調(diào)隘蝎，因此Java層需要構(gòu)造responseMsg
//從message中取出callbackId，放進(jìn)responseMsg
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;
//從message中取出Handler名字襟企，再?gòu)膍essageHandlers中取
//如果沒(méi)有就使用默認(rèn)的Handler
if (!TextUtils.isEmpty(m.getHandlerName())) {
handler = messageHandlers.get(m.getHandlerName());
} else {
handler = defaultHandler;
}
if (handler != null){
//執(zhí)行handler
handler.handler(m.getData(), responseFunction);
}
}
}
}
});
}
}
那么這個(gè)handler是什么嘱么？就是Java調(diào)用registerHandler注冊(cè)的getUserInfo
private void registerHandler() {
mBridgeWebView.registerHandler("getUserInfo", new BridgeHandler() {
@Override
public void handler(String data, CallBackFunction function) {
Log.i(TAG, "handler = getUserInfo, data from web = " + data);
function.onCallBack(new Gson().toJson(mUserInfo));
}
}
上面的function就是在flushMessageQueue 解析時(shí)構(gòu)造的responseFunction，在message中包括JS層需要回調(diào)的函數(shù)Id顽悼，然后就是getUserInfo執(zhí)行的結(jié)果
調(diào)用queueMessage
responseFunction = new CallBackFunction() {
@Override
public void onCallBack(String data) {
Message responseMsg = new Message();
responseMsg.setResponseId(callbackId);
responseMsg.setResponseData(data);
queueMessage(responseMsg);
}
};
queueMessage調(diào)用dispatchMessage發(fā)送message給JS
通過(guò)構(gòu)造String指令曼振，然后loadUrl執(zhí)行JS代碼,注意對(duì)象也是通過(guò)這樣方式傳遞過(guò)去的几迄，就類似調(diào)用本地函數(shù)，不發(fā)起網(wǎng)絡(luò)請(qǐng)求
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);
if (Thread.currentThread() == Looper.getMainLooper().getThread()) {
this.loadUrl(javascriptCommand);
}
}
其中
BridgeUtil.JS_HANDLE_MESSAGE_FROM_JAVA ="javascript:WebViewJavascriptBridge._handleMessageFromNative('%s');"
javascriptCommand = javascript:WebViewJavascriptBridge._handleMessageFromNative('{\"responseData\":\"{\\\"email\\\":\\\"jue@126.com\\\"}\",\"responseId\":\"cb_1_1495182558893\"}');
//data = {\"responseData\":\"{\\\"email\\\":\\\"jue@126.com\\\"}\",\"responseId\":\"cb_1_1495182409011\"}
- JS收到Response JSON
來(lái)到_handleMessageFromNative冰评，
function _handleMessageFromNative(messageJSON) {
console.log(messageJSON);
if (receiveMessageQueue && receiveMessageQueue.length > 0) {
receiveMessageQueue.push(messageJSON);
} else {
_dispatchMessageFromNative(messageJSON);
}
}
最后都會(huì)調(diào)用到_dispatchMessageFromNative映胁，由于是JS主動(dòng)調(diào)用Java，因此有responseId集索，執(zhí)行registerHandler時(shí)傳入的CallBack屿愚，也就是顯示用戶信息。我在代碼里加了注釋务荆，很容易看懂妆距。
function _dispatchMessageFromNative(messageJSON) {
setTimeout(function() {
//將數(shù)據(jù)解析成JSON
var message = JSON.parse(messageJSON);
var responseCallback;
//java call finished, now need to call js callback function
//根據(jù)responseId:cb_1_1495182409011拿到responseCallback，就是我們前門注冊(cè)的alert
if (message.responseId) {
responseCallback = responseCallbacks[message.responseId];
if (!responseCallback) {
return;
}
responseCallback(message.responseData);
delete responseCallbacks[message.responseId];
} else {
//直接發(fā)送
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];
}
//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);
}
}
}
});
}
源碼的分析就到這結(jié)束了函匕，代碼不多娱据，但是封裝的接口很是好用。最后再來(lái)個(gè)分割線～～
3.總結(jié)
最后總結(jié)下盅惜，使用上很方便主要兩個(gè)步驟
被調(diào)用方注冊(cè)Handler
registerHandler(String handlerName, BridgeHandler handler)
調(diào)用方調(diào)用Handler
callHandler(String handlerName, String data, CallBackFunction callBack)
原理上還是那三句話中剩，請(qǐng)?jiān)徫覐纳厦嬷苯觕opy過(guò)來(lái)：
1.Android調(diào)用JS是通過(guò)loadUrl(url),url中可以拼接要傳給JS的對(duì)象
2.JS調(diào)用Android是通過(guò)shouldOverrideUrlLoading
3.JsBridge將溝通數(shù)據(jù)封裝成Message，然后放進(jìn)Queue,再將Queue進(jìn)行傳輸
好了抒寂，今天我們JsBridge的使用和源碼分析就到這了结啼，謝謝！
文中栗子的鏈接：
https://github.com/juexingzhe/Android_JS
歡迎關(guān)注公眾號(hào)：JueCode
