CEF_JavaScript_Cpp.md

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CefRenderProcessHandlerImpl
   void 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.h
   class 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.cpp
   bool 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js
   	if(!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();
   	}
   }