VB.net WebBrowser网页元素抓取分析方法

在用WebBrowser编程实现网页操作自动化时，常要分析网页Html，例如网页在加载数据时，常会显示“系统处理中，请稍候..”，我们需要在数据加载完成后才能继续下一步操作，如何抓取这个信息的网页html元素变化，从而判断数据加载完毕呢？用IE开发者工具是不可能抓取到的，太快了。(当然，设置足够长的延时，也是可以实现的，只是不够科学及稳妥，毕竟有时因为网络原因，数据加载时间可能超过原来设定时间，其次，设置延时过长也导致程序不够友好）

实现的办法：

1、先用“系统处理中”查找（泛查找），并在找到html中，再细找缩小html元素范围。

bb = FindHtmlElement("系统处理中", ExtendedWebBrowser1.Document, "", "InnerText", false)

2、添加一个Timer控件，设定100毫秒。根据 1中找到的元素，进行不断抓取，并将抓到的结果输出到文本。

3、将2中输出，导入Excel，进行筛选，并从中找到重复次数少的行，便是数据加载、加载完成之间的变化。

Private Sub TimerProgress_Tick(sender As Object, e As EventArgs) Handles TimerProgress.TickIf Gethtmel ThenDim bb As HtmlElementbb = FindHtmlElement("all_jzts", ExtendedWebBrowser1.Document, "div", "id", True)If Not bb Is Nothing Then'WriteRunLog("Style ：  " + bb.Style)WriteRunLog(bb.OuterHtml)ElseWriteRunLog("all_jzts没找到")End Ifbb = FindHtmlElement("jzts", ExtendedWebBrowser1.Document, "div", "id", True)If Not bb Is Nothing Then'WriteRunLog("Style ：  " + bb.Style)WriteRunLog(bb.OuterHtml)ElseWriteRunLog("jzts没找到")End If'Gethtmel = FalseEnd If'系统处理中，请稍候...Application.DoEvents()End Sub

 Function FindHtmlElement(ByVal FindText As String, ByVal doc As HtmlDocument, ByVal cTagName As String, ByVal cGetAttribute As String, Optional ByVal StrictMatching As Boolean = False) As HtmlElement'cTagName：检索具有指定 html 标记的元素，标记需要输入完整的，缺省时查找所有。'例如：<input class="button" type="submit" value=提交 style="cursor:hand">，不能只输入"i"，需要输入"input"'cGetAttribute ：比较的属性类型，取值为：Id、InnerText、Name、title、classname、value、'Id、InnerText可以通过GetAttribute获取，也可以通过HtmlElement.Id、HtmlElement.InnerText获取，所以代码简化为用GetAttribute获取。'doc：WebBrowserExt1.Document'GetAttribute("classname")   '例如显示class="commonTable"的值commonTable'StrictMatching：True严格匹配FindText'WriteRunLog("FindHtmlElement开始：" + FindText)TryDim i, k As IntegerFindHtmlElement = NothingFindHtmlElementOfDocument = docIf doc Is Nothing Then  '2023.11.15在递归调用中，因为有些iFrames还未真正加载，从而导致传入的doc = doc.Window.Frames.Item(k).Document 为 Nothing ，从而引发异常：未将对象引用设置到对象的实例。Exit FunctionEnd IfIf LCase(cGetAttribute) = "innertext" Then  'InnerText必须严格匹配，否则找到的结果是错误的。’StrictMatching = TrueEnd IfIf cTagName <> "" ThenDim EE As HtmlElementCollection = doc.GetElementsByTagName(cTagName)For i = 0 To EE.Count - 1If InStr(EE.Item(i).GetAttribute(cGetAttribute), FindText) > 0 _And (Not StrictMatching Or InStr(FindText, EE.Item(i).GetAttribute(cGetAttribute)) > 0) ThenFindHtmlElement = EE.Item(i)'WriteRunLog("Loop1")'WriteRunLog("FindHtmlElement结束0")Exit Function                       '找到就退出End IfNextElseFor i = 0 To doc.All.Count - 1If InStr(doc.All.Item(i).GetAttribute(cGetAttribute), FindText) > 0 _And (Not StrictMatching Or InStr(FindText, doc.All.Item(i).GetAttribute(cGetAttribute)) > 0) And (cTagName = "" Or LCase(cTagName) = LCase(doc.All.Item(i).TagName)) ThenFindHtmlElement = doc.All.Item(i)'WriteRunLog("Loop1")'WriteRunLog("FindHtmlElement结束0")Exit Function                       '找到就退出End IfNextEnd If'上面没找到，进行递归调用，递归会查找所有嵌套的Frame。For k = 0 To doc.Window.Frames.Count - 1'If k = 0 Then'    WriteRunLog("递归调用 doc.Window.Frames.Count：" + doc.Window.Frames.Count.ToString)     'For Test'End If'2018.3.14 直接 递归调用'WriteRunLog("递归调用：" + Str(k))' WriteRunLog("doc.Window.Frames.Item(k).Name：" + doc.Window.Frames.Item(k).Name)FindHtmlElementOfDocument = doc.Window.Frames.Item(k).DocumentFindHtmlElement = FindHtmlElement(FindText, doc.Window.Frames.Item(k).Document, cTagName, cGetAttribute, StrictMatching)If Not FindHtmlElement Is Nothing Then  '找到就退出循环'WriteRunLog("FindHtmlElement结束1")Exit FunctionEnd IfNextCatch ex As ExceptionFindHtmlElement = NothingWriteRunLog("FindHtmlElement发生异常：" + ex.Message)End TryEnd FunctionSub WriteRunLog(ByVal MyMsg As String)'Using w As StreamWriter = File.AppendText("RunLog.txt")Dim w As StreamWriterIf File.Exists("RunLog.txt") ThenIf My.Computer.FileSystem.GetFileInfo("RunLog.txt").Length > 10485760 Then  '2017.5.4 文件大于10M，清0w = File.CreateText("RunLog.txt")w.Write("文件大于10M，置0从头开始！")w.Write(Chr(9))Elsew = File.AppendText("RunLog.txt")End IfElsew = File.CreateText("RunLog.txt")End Ifw.Write(Now)w.Write(Chr(9))     '插入Tab键w.WriteLine(MyMsg)w.Flush()w.Close()'End UsingEnd Sub