请问，调用cef库，用注册回调js的方法，实现c++调用js，为什么只能在继承了v8中Execute的方法里调用，保存，context 和 call_back后在别的函数里还是不能调用？

Question

参考了https://blog.csdn.net/CAir2/article/details/91576805这篇博客

继承v8的Execute函数， 

```bool ClientV8ExtensionHandler::Execute(const CefString& func_name,
    CefRefPtr<CefV8Value> object,
    const CefV8ValueList& arguments,
    CefRefPtr<CefV8Value>& retval,
    CefString& exception)
{
    if (func_name == L"register")
    {
        if (arguments.size() == 1 && arguments[0]->IsFunction())
        {
            CefRefPtr<CefV8Context> context = CefV8Context::GetCurrentContext();
            CefRefPtr<CefV8Value> call_back = arguments[0];
            //由于这里只是一个demo，所以把funcid固定为1，如果存在多个注册回调函数，请维护funcid和callback的关系
            //if (m_render_app)
            //  m_render_app->AddCallBack(1, context, call_back);

            //调用回调,进入上下文
            context->Enter();

            CefV8ValueList call_arguments;
            call_arguments.push_back(CefV8Value::CreateString(_T("hellow word")));
            //调用回调函数，回调参数
            call_back->ExecuteFunction(NULL, call_arguments);

            //退出上下文
            context->Exit();
            return true;
        }
    }



    else if (func_name == L"ReadID")
    {
        if (arguments.size() == 1 && arguments[0]->IsFunction())
        {
            CPublic::ReadID_context = CefV8Context::GetCurrentContext();//保存context
            CPublic::browser = CPublic::ReadID_context->GetBrowser();//保存call_back 
            CPublic::ReadID_call_back = arguments[0];
            HWND hwnd = AfxGetApp()->GetMainWnd()->GetSafeHwnd();
            ::PostMessage(hwnd, WM_MYMSGReadID, 0, 0);//发送消息到主窗口执行消息函数
            return true;
    }


    else
    {
        return false;
    }
}

调用的消息函数

LRESULT CMFCApplication1Dlg::OnMyMsgReadID(WPARAM H, LPARAM J)
{
    //CPublic::ReadID_context->GetBrowser() = CPublic::browser;
    //CefRefPtr<CefBrowser> browser = CPublic::ReadID_context->GetBrowser();

    if (CPublic::ReadID_context&&CPublic::ReadID_call_back)
    {
        CPublic::ReadID_context->Enter();//一定要先Enter

        if (CPublic::ReadID_context->GetBrowser()) //判断上下文中的Browser是否存在
        {
            ////处理任务，并且执行回调

            CefV8ValueList call_arguments;
            call_arguments.push_back(CefV8Value::CreateString(_T("123456")));
            CPublic::ReadID_call_back->ExecuteFunctionWithContext(NULL,NULL, call_arguments);
        }
        CPublic::ReadID_context->Exit();//退出Context
        //m_CallBackMap.erase(callbackId);

    }
    return 0;
    }

注册的回调方法
void CCefBrowserApp::OnWebKitInitialized()
{
std::string extensionCode =
"var g_value=\"global value here\";"
"var MyMath;"
"if (!MyMath)"
" MyMath = {};"
"(function() {"
" MyMath.register = function(call_back) {"
" native function register(call_back);"
" return register(call_back);"
" MyMath.hellow = 'Hello JS!';"//定义一个MyMath的成员变量"
" };"
" MyMath.ReadID = function(call_back) {"
" native function ReadID(call_back);"
" return ReadID(call_back);"
" };"
"})();";

    CefRefPtr<CefV8Handler> handler = new ClientV8ExtensionHandler();

// Register the extension.
CefRegisterExtension("v8/test", extensionCode, handler);

}

Answer 1

这是变量作用域的问题，不同的脚本不在一个作用域里