使用CefSharp和Javascript实现网络爬虫-Javascript和C#交互

在爬虫实现过程中，采用Javascript的DOM操作来抓取目标数据，并通过CefSharp提供的Javascript和C#交互方法，把目标数据传递给C#代码进行处理。上一篇介绍了采用Javascript的DOM操作来抓取目标数据，这一篇介绍CefSharp中Javascript和C#之间的调用和交互，以及使用C#委托实现回调处理。

一、CefSharp中Javascript和C#之间的调用和交互

1、C#调用Javascript

private ChromiumWebBrowser myBrowser;
myBrowser.GetBrowser().MainFrame.ExecuteJavaScriptAsync("console.log('helloworld');");
2、Javascript调用C#，实现数据上报

(1)C#暴露接口定义

public class AsyncJavascriptBindingClass{
public int ReceiveMsg (int nType, string msg){
Console.WriteLine("AsyncJavascriptBindingClass. ReceiveMsg: " + nType + "," + msg);
}
}
(2)C#暴露接口注册

myBrowser.JavascriptObjectRepository.ResolveObject += (_sender, _e) =>{
var repo = _e.ObjectRepository;
if (_e.ObjectName == "boundAsync"){
repo.Register("boundAsync", new AsyncJavascriptBindingClass(), isAsync: true);
}
};
(3)在Javascript中调用

async function sendMsg(type,msg){
await CefSharp.BindObjectAsync('boundAsync');
var result = await boundAsync. ReceivMsg(type,msg);
};
sendMsg (1, 'hello C#');
二、C#委托使用

当C#代码接收到Javascript传递的目标数据后，常常需要通知其他处理线程进行后续处理，例如通知主界面线程改变当前访问的URL地址等，这里介绍我在实现爬虫过程中使用C#委托实现回调机制。

(1)定义委托类

public delegate void CallBackDelegate(string msg);
(2)在AsyncJavascriptBindingClass中触发回调函数

public class AsyncJavascriptBindingClass{
public CallBackDelegate callBack;
public AsyncJavascriptBindingClass(CallBackDelegate _callBack){
this.callBack = _callBack;
}
public int ReceivMsg (int nType, string msg){
callback(msg); //todo
}
｝
(3)在主界面对象WindowForm中实现回调函数

private void CallBack(string msg){
//your code
｝
myBrowser.JavascriptObjectRepository.ResolveObject += (_sender, _e) =>{
var repo = _e.ObjectRepository;
if (_e.ObjectName == "boundAsync"){
repo.Register("boundAsync", new AsyncJavascriptBindingClass(CallBack), isAsync: true);
}
};