CEF JavaScript和Cpp交互示例(Custom Implementation)

一个CEF应用程序也可以提供自己的异步JavaScript绑定。

此处演示：

• JavaScript注册函数给Render进程，Render进程保存该JavaScript函数
• Render进程发消息通知Browser进程
• Browser进程处理后，回发消息给Render进程
• Render进程调用之前保存的JavaScript函数

步骤

1. 首先在CefRenderProcessHandler的子类里覆写虚方法OnWebKitInitialized，并在该方法的实现里注册一个C++方法给JavaScript

   //假设CefRenderProcessHandler的子类为CefRenderProcessHandlerImplvoid CefRenderProcessHandlerImpl::OnWebKitInitialized(){std::string app_code =//-----------------------------------//声明JavaScript里要调用的Cpp方法"var app;""if (!app)""  app = {};""(function() {"//  Send message "  app.sendMessage = function(name, arguments) {""    native function sendMessage();""    return sendMessage(name, arguments);""  };"// Registered Javascript Function, which will be called by Cpp"  app.registerJavascriptFunction = function(name,callback) {""    native function registerJavascriptFunction();""    return registerJavascriptFunction(name,callback);""  };""})();";//------------------------------------// Register app extension module// JavaScript里调用app.registerJavascriptFunction时，就会去通过CefRegisterExtension注册的CefV8Handler列表里查找// 找到"v8/app"对应的CefV8HandlerImpl，就调用它的Execute方法// 假设m_v8Handler是CefRenderProcessHandlerImpl的一个成员变量m_v8Handler = new CefV8HandlerImpl();CefRegisterExtension("v8/app", app_code,m_v8Handler);}

2. 在CefV8Handler的子类的Execute方法里实现sendMessage和registerJavascriptFunction

   // in CefV8HandlerImpl.hclass CefV8HandlerImpl : publice CefV8Handler{public:CefV8HandlerImpl();~CefV8HandlerImpl();public:/** *CefV8Handler Methods, Which will be called when the V8 extension  *  is called in the Javascript environment */virtual bool Execute(const CefString& name,CefRefPtr<CefV8Value> object,const CefV8ValueList& arguments,CefRefPtr<CefV8Value>& retval,CefString& exception);private:// Map of message callbacks.typedef std::map<std::pair<std::string, int>, std::pair<CefRefPtr<CefV8Context>, CefRefPtr<CefV8Value> > > CallbackMap;CallbackMap callback_map_;}

   CefV8HandlerImpl::CefV8HandlerImpl(){}CefV8HandlerImpl::~CefV8HandlerImpl(){  // Remove any JavaScript callbacks registered for the context that has been released.  if (!callback_map_.empty()) {CallbackMap::iterator it = callback_map_.begin();for (; it != callback_map_.end();) {  if (it->second.first->IsSame(context))callback_map_.erase(it++);  else++it;}  }}// in CefV8HandlerImpl.cppbool CefV8HandlerImpl::Execute(const CefString& name  //JavaScript调用的C++方法名字,CefRefPtr<CefV8Value> object                 //JavaScript调用者对象,const CefV8ValueList& arguments              //JavaScript传递的参数,CefRefPtr<CefV8Value>& retval                //需要返回给JavaScript的值设置给这个对象,CefString& exception)                        //通知异常信息给JavaScript{// In the CefV8Handler::Execute implementation for “registerJavascriptFunction”.bool handle=false;if(name=="registerJavascriptFunction"){//保存JavaScript设置的回答函数if (arguments.size() == 2 && arguments[0]->IsString() &&arguments[1]->IsFunction()) {  std::string message_name = arguments[0]->GetStringValue();  CefRefPtr<CefV8Context> context = CefV8Context::GetCurrentContext();  int browser_id = context->GetBrowser()->GetIdentifier();  callback_map_.insert(  std::make_pair(std::make_pair(message_name, browser_id), std::make_pair(context, arguments[1])));handle = true;// 此时可以发送一个信息给Browser进程，见第4个步骤}if(name=="sendMessage"){//处理SendMessage，handle = true;}// 如果没有处理，则发异常信息给jsif(!handle){exception="not implement function";}return true;}

3. 在HTML的JavaScript里，通过上面注册的方法向Render进程注册一个回调函数。

   // In JavaScript register the callback function.app.setMessageCallback('binding_test', function(name, args) {  document.getElementById('result').value = "Response: "+args[0];});

4. Render进程发送异步进程间通信到Browser进程。

5. Browser进程接收到进程间消息，并处理。

6. Browser进程处理完毕后，发送一个异步进程间消息给Render进程，返回结果。

7. Render进程接收到进程间消息，则调用最开始保存的JavaScript注册的回调函数处理之。

   // Execute the registered JavaScript callback if any.if (!callback_map_.empty()) {  const CefString& message_name = message->GetName();  CallbackMap::const_iterator it = callback_map_.find(  std::make_pair(message_name.ToString(), browser->GetIdentifier()));  if (it != callback_map_.end()) {// Keep a local reference to the objects. The callback may remove itself// from the callback map.CefRefPtr<CefV8Context> context = it->second.first;CefRefPtr<CefV8Value> callback = it->second.second;// Enter the context.context->Enter();CefV8ValueList arguments;// First argument is the message name.arguments.push_back(CefV8Value::CreateString(message_name));// Second argument is the list of message arguments.CefRefPtr<CefListValue> list = message->GetArgumentList();CefRefPtr<CefV8Value> args = CefV8Value::CreateArray(list->GetSize());SetList(list, args);  // Helper function to convert CefListValue to CefV8Value.arguments.push_back(args);// Execute the callback.CefRefPtr<CefV8Value> retval = callback->ExecuteFunction(NULL, arguments);if (retval.get()) {  if (retval->IsBool())handled = retval->GetBoolValue();}// Exit the context.context->Exit();  }}

8. 在CefRenderProcessHandlerImpl::OnContextReleased()里释放JavaScript注册的回调函数以及其他V8资源。

   void CefRenderProcessHandlerImpl::OnContextReleased(CefRefPtr<CefBrowser> browser,  CefRefPtr<CefFrame> frame,  CefRefPtr<CefV8Context> context) {if(m_v8Handler->Get()){m_v8Handler->Release();}}