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在CEF里,JS和Native(C/C++)代码可以很方便的交互,这里https://bitbucket.org/chromiumembedded/cef/wiki/JavaScriptIntegration.md讲解得很清楚。我照着它实现了一个简单的交互示例。
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在贴代码之前,先来看看Browser进程和Render进程是怎么回事儿,有什么不同。
Browser与Render进程
从cefsimple开始吧,cefsimple_win.cc中的wWinMain函数中调用了CefExecuteProcess()方法来检测是否要启动其它的子进程。此处的CefExecuteProcess是在libcef_dll_wrapper.cc中的,它内部又调用了cef_execute_process方法(libcef_dll.cc),cef_execute_process又调用了libcef/browser/context.cc文件内实现的CefExecuteProcess方法。这个方法代码如下:
int CefExecuteProcess(const CefMainArgs& args, CefRefPtr<CefApp> application, void* windows_sandbox_info) { base::CommandLine command_line(base::CommandLine::NO_PROGRAM);#if defined(OS_WIN) command_line.ParseFromString(::GetCommandLineW());#else command_line.InitFromArgv(args.argc, args.argv);#endif // Wait for the debugger as early in process initialization as possible. if (command_line.HasSwitch(switches::kWaitForDebugger)) base::debug::WaitForDebugger(60, true); // If no process type is specified then it represents the browser process and // we do nothing. std::string process_type = command_line.GetSwitchValueASCII(switches::kProcessType); if (process_type.empty()) return -1; CefMainDelegate main_delegate(application); // Execute the secondary process.#if defined(OS_WIN) sandbox::SandboxInterfaceInfo sandbox_info = {0}; if (windows_sandbox_info == NULL) { content::InitializeSandboxInfo(&sandbox_info); windows_sandbox_info = &sandbox_info; } content::ContentMainParams params(&main_delegate); params.instance = args.instance; params.sandbox_info = static_cast<sandbox::SandboxInterfaceInfo*>(windows_sandbox_info); return content::ContentMain(params);#else content::ContentMainParams params(&main_delegate); params.argc = args.argc; params.argv = const_cast<const char**>(args.argv); return content::ContentMain(params);#endif
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它分析了命令行参数,提取”type”参数,如果为空,说明是Browser进程,返回-1,这样一路回溯到wWinMain方法里,然后开始创建Browser进程相关的内容。
如果”type”参数不为空,做一些判断,最后调用了content::ContentMain方法,直到这个方法结束,子进程随之结束。
content::ContentMain方法再追溯下去,就到了chromium的代码里了,在chromium/src/content/app/content_main.cc文件中。具体我们不分析了,感兴趣的可以去看看。
分析了CefExecuteProcess方法我们知道,Browser进程在cefsimple_win.cc内调用了CefExecuteProcess之后做了进一步的配置,这个是在simple_app.cc内完成的,具体就是SimpleApp::OnContextInitialized()这个方法,代码如下:
void SimpleApp::OnContextInitialized() { CEF_REQUIRE_UI_THREAD(); CefWindowInfo window_info; window_info.SetAsPopup(NULL, "cefsimple"); // SimpleHandler implements browser-level callbacks. CefRefPtr<SimpleHandler> handler(new SimpleHandler()); // Specify CEF browser settings here. CefBrowserSettings browser_settings; std::string url; CefRefPtr<CefCommandLine> command_line = CefCommandLine::GetGlobalCommandLine(); url = command_line->GetSwitchValue("url"); if (url.empty()) url = "http://www.google.com"; CefBrowserHost::CreateBrowser(window_info, handler.get(), url, browser_settings, NULL);}
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可以看到,这里创建SimpleHandler,并传递给CefBrowserHost::CreateBrowser去使用。
现在我们清楚了,Browser进程,需要CefApp(SimpleApp实现了这个接口)和CefClient(SimpleHandler实现了这个接口)。而Renderer进程只要CefApp。
另外,CEF还定义了CefBrowserProcessHandler和CefRenderProcessHandler两个接口,分别来处理Browser进程和Render进程的个性化的通知。因此,Browser进程的App一般还需要实现CefBrowserProcessHandler接口,Renderer进程的App一般还需要实现CefRenderProcessHandler接口。这里https://bitbucket.org/chromiumembedded/cef/wiki/GeneralUsage有详细说明。
像cefsimple这个示例中的SimpeApp,没有实现CefRenderProcessHandler接口,没有针对Renderer进程做特别处理,所以当它作为Render进程时,会缺失一部分功能。比如JS与Native代码交互,这正是我们想要的。
如果要实现JS与Native代码交互,最好分开实现Browser进程需要的CefApp和Render进程需要的CefApp。像下面这样:
class ClientAppRenderer : public CefApp, public CefRenderProcessHandler { ...}class ClientAppBrowser : public CefApp, public CefBrowserProcessHandler{ ...}
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当我们实现了CefRenderProcessHandler接口,就可以在其OnContextCreated()方法中获取到CefFrame对应的window对象,在它上面绑定一些JS函数或对象,然后JS代码里就可以通过window对象访问,如果是函数,就会调用到我们实现的CefV8Handler接口的Execute方法。
另外一种实现JS与Native交互的方式,是在实现CefRenderProcessHandler的OnWebKitInitialized()方法时导出JS扩展,具体参考https://bitbucket.org/chromiumembedded/cef/wiki/JavaScriptIntegration.md,有详细说明。
cef_js_integration项目
cef_js_integration是非常简单的示例,用来演示JS与Native的交互。它在一个项目内实现了ClientAppBrowser、ClientAppRenderer、ClientAppOther三种CefApp,分别对应Browser、Render及其它类别的三种进程。
JS和Native代码的交互发生在Render进程,App需要继承CefRenderProcessHandler来整合JS相关功能。因此在应用在启动时做了进程类型判断,根据不同的进程类型创建不同的CefApp。
这个示例演示了三种JS交互方式(参见https://bitbucket.org/chromiumembedded/cef/wiki/JavaScriptIntegration.md):
- 在native代码中通过CefFrame::ExecuteJavaScript()来执行JavaScript代码
- 将函数或对象绑定到CefFrame对应的window对象上,JS代码通过window对象访问native代码导出的函数或对象
- 使用CefRegisterExtension()注册JS扩展,JS直接访问注册到JS Context中的对象
这个项目参考了cefsimple、cefclient,还有https://github.com/acristoffers/CEF3SimpleSample,最终它比cefsimple复杂一点,比cefclient简单很多。
好啦,背景差不多,上源码。
cef_js_integration.cpp:
#include <windows.h>#include <tchar.h>#include "cef_js_integration.h"#include <string>#include <algorithm>#include "include/cef_app.h"#include "include/cef_browser.h"#include "ClientAppBrowser.h"#include "ClientAppRenderer.h"#include "ClientAppOther.h"#include "include/cef_command_line.h"#include "include/cef_sandbox_win.h"//#define CEF_USE_SANDBOX 1#if defined(CEF_USE_SANDBOX)#pragma comment(lib, "cef_sandbox.lib")#endifint APIENTRY _tWinMain(_In_ HINSTANCE hInstance, _In_opt_ HINSTANCE hPrevInstance, _In_ LPTSTR lpCmdLine, _In_ int nCmdShow){ UNREFERENCED_PARAMETER(hPrevInstance); UNREFERENCED_PARAMETER(lpCmdLine); // Enable High-DPI support on Windows 7 or newer. CefEnableHighDPISupport(); CefMainArgs main_args(hInstance); void* sandbox_info = NULL;#if defined(CEF_USE_SANDBOX) CefScopedSandboxInfo scoped_sandbox; sandbox_info = scoped_sandbox.sandbox_info();#endif // Parse command-line arguments. CefRefPtr<CefCommandLine> command_line = CefCommandLine::CreateCommandLine(); command_line->InitFromString(::GetCommandLineW()); // Create a ClientApp of the correct type. CefRefPtr<CefApp> app; // The command-line flag won't be specified for the browser process. if (!command_line->HasSwitch("type")) { app = new ClientAppBrowser(); } else { const std::string& processType = command_line->GetSwitchValue("type"); if (processType == "renderer") { app = new ClientAppRenderer(); } else { app = new ClientAppOther(); } } // Execute the secondary process, if any. int exit_code = CefExecuteProcess(main_args, app, sandbox_info); if (exit_code >= 0) return exit_code; // Specify CEF global settings here. CefSettings settings;#if !defined(CEF_USE_SANDBOX) settings.no_sandbox = true;#endif // Initialize CEF. CefInitialize(main_args, settings, app.get(), sandbox_info); // Run the CEF message loop. This will block until CefQuitMessageLoop() is // called. CefRunMessageLoop(); // Shut down CEF. CefShutdown(); return 0;}
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可以看到,_tWinMain方法中解析了命令行参数,根据进程类型创建了不同的CefApp。这是它与cefsimple的区别。
ClientAppBrowser类与cefsimple示例中的SimpleApp基本一致,略过。
ClientAppRender类在ClientAppRender.h和ClientAppRender.cpp中实现。先是ClientAppRender.h:
#ifndef CEF3_CLIENT_APP_RENDERER_H#define CEF3_CLIENT_APP_RENDERER_H#include "include/cef_app.h"#include "include/cef_client.h"#include "V8handler.h"class ClientAppRenderer : public CefApp, public CefRenderProcessHandler {public: ClientAppRenderer(); CefRefPtr<CefRenderProcessHandler> GetRenderProcessHandler() OVERRIDE { return this; } void OnContextCreated( CefRefPtr<CefBrowser> browser, CefRefPtr<CefFrame> frame, CefRefPtr<CefV8Context> context); void OnWebKitInitialized() OVERRIDE;private: CefRefPtr<ClientV8Handler> m_v8Handler; IMPLEMENT_REFCOUNTING(ClientAppRenderer);};#endif
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ClientAppRender聚合了ClientV8Handler类的实例,回头再说。先来看ClientAppRender的OnContextCreated和OnWebKitInitialized,它们是实现JS与Native交互的关键。代码如下:
#include "ClientAppRenderer.h"#include "V8handler.h"#include <Windows.h>#include <tchar.h>ClientAppRenderer::ClientAppRenderer() : m_v8Handler(new ClientV8Handler){}void ClientAppRenderer::OnContextCreated(CefRefPtr<CefBrowser> browser, CefRefPtr<CefFrame> frame, CefRefPtr<CefV8Context> context){ OutputDebugString(_T("ClientAppRenderer::OnContextCreated, create window binding\r\n")); // Retrieve the context's window object. CefRefPtr<CefV8Value> object = context->GetGlobal(); // Create the "NativeLogin" function. CefRefPtr<CefV8Value> func = CefV8Value::CreateFunction("NativeLogin", m_v8Handler); // Add the "NativeLogin" function to the "window" object. object->SetValue("NativeLogin", func, V8_PROPERTY_ATTRIBUTE_NONE);}void ClientAppRenderer::OnWebKitInitialized(){ OutputDebugString(_T("ClientAppRenderer::OnWebKitInitialized, create js extensions\r\n")); std::string app_code = "var app;" "if (!app)" " app = {};" "(function() {" " app.GetId = function() {" " native function GetId();" " return GetId();" " };" "})();"; CefRegisterExtension("v8/app", app_code, m_v8Handler);}
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OnContextCreated给window对象绑定了一个NativeLogin函数,这个函数将由ClientV8Handler类来处理,当HTML中的JS代码调用window.NativeLogin时,ClientV8Handler的Execute方法会被调用。
OnWebKitInitialized注册了一个名为app的JS扩展,在这个扩展里为app定义了GetId方法,app.GetId内部调用了native版本的GetId()。HTML中的JS代码可能如下:
alert(app.GetId());
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当浏览器执行上面的代码时,ClientV8Handler的Execute方法会被调用。
好啦,现在来看ClientV8Handler的实现(V8Handler.cpp):
#include "V8handler.h"#include <Windows.h>#include <tchar.h>bool ClientV8Handler::Execute(const CefString& name, CefRefPtr<CefV8Value> object, const CefV8ValueList& arguments, CefRefPtr<CefV8Value>& retval, CefString& exception) { if (name == "NativeLogin") { if (arguments.size() == 2) { CefString strUser = arguments.at(0)->GetStringValue(); CefString strPassword = arguments.at(1)->GetStringValue(); TCHAR szLog[256] = { 0 }; _stprintf_s(szLog, 256, _T("user - %s, password - %s\r\n"), strUser.c_str(), strPassword.c_str()); OutputDebugString(szLog); //TODO: doSomething() in native way retval = CefV8Value::CreateInt(0); } else { retval = CefV8Value::CreateInt(2); } return true; } else if (name == "GetId") { if (arguments.size() == 0) { // execute javascript // just for test CefRefPtr<CefFrame> frame = CefV8Context::GetCurrentContext()->GetBrowser()->GetMainFrame(); frame->ExecuteJavaScript("alert('Hello, I came from native world.')", frame->GetURL(), 0); // return to JS retval = CefV8Value::CreateString("72395678"); return true; } } // Function does not exist. return false;}
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Execute在处理GetId方法时,还使用CefFrame::ExecuteJavaScript演示了如何在native代码中执行JS代码。
最后,来看一下html代码:
<!DOCTYPE html><html> <!-- Copyright (c) 2016 foruok. All rights reserved. 欢迎关注foruok的微信订阅好“程序视界”。 --><head> <script type="text/javascript"> function Login(){ window.NativeLogin(document.getElementById("userName").value, document.getElementById("password").value); } function GetId(){ alert("get id from native by extensions: " + app.GetId()); } </script> <title>CEF JS Integration</title></head><body><h3>Call into native by Window bindings:</h3><form>UserName: <input type="text" id="userName" /> Password: <input type="text" id="password" /> <input type="button" value="Login" onclick="Login()"/></form><hr><h3>Call into native by js extensions:</h3><input type="button" value="GetId" onclick="GetId()"/></html>
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通过下面的命令可以测试:
cef_js_integration.exe --url=file:///cef_js_integration.html
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好啦,JS与Native交互的示例就到这里了。
其他参考文章:
- CEF Windows开发环境搭建
- CEF加载PPAPI插件
- VS2013编译最简单的PPAPI插件
- 理解PPAPI的设计
- PPAPI插件与浏览器的交互过程
- Windows下从源码编译CEF
- 编译PPAPI的media_stream_video示例
- PPAPI插件的绘图与输入事件处理
- 在PPAPI插件中创建本地窗口
- PPAPI插件与浏览器的通信
- Windows下从源码编译Skia
- 在PPAPI插件中使用Skia绘图
- 加载DLL中的图片资源生成Skia中的SkBitmap对象
- PPAPI+Skia实现的涂鸦板
- PPAPI中使用Chromium的3D图形接口
- PPAPI中使用OpenGL ES绘图