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 使用《VB.net webbrowser 如何实现自定义下载 IDownloadManager》中的控件ExtendedWebBrowser（下载控件），并扩展了NewWindow2。

使用ExtendedWebBrowser_1过程中，遇到很多问题，花了几天时间，终于解决了所有问题。

问题1：接管了下载后，发现大文件下载，主程序会阻塞。

        一开始，以为是在写文件时因为IO响应导致阻塞，改用异步写，等等...尝试，发现阻塞依然，看过《C# 用FileStream.WriteAsync 异步读文件，调用线程还是被阻塞了》等文章后，问题依然未能解决。

        最后尝试主程序不写文件（就是接管下载后，在OnDataAvailable中对接收数据不操作），不做任何操作，阻塞依然存在。阻塞会导致下载中断，而且这种情况与下载文件大小无关，即使很小几M的文件也会发生。

        苦思中，记起以前写一个延时函数时，为了不阻塞而加入了Application.DoEvents()语句，于是在最频繁操作的OnDataAvailable中加入Application.DoEvents()语句，问题终于得到完满解决。

问题2：写文件

        一开始，是主程序写文件，遇到太多麻烦，在解决问题1中，发现接管了下载后，其实IE是有在后台进程中将文件下载到IE缓冲区的，OnProgress第一次便是返回IE缓冲区中下载的文件名，于是便改用：等下载完后从IE缓冲区复制文件。（貌似IE原有下载器也是这样干的？）

问题3：对于会弹出新窗口的下载，在进行第二次下载时，没有触发下载。

        因为主程序中接管弹出窗口的Extendedwebbrowser_2一直没关闭（IE中下载窗口是立即关闭的），并且发现，在NewWindow2中将弹出下载转到Extendedwebbrowser_2触发下载时，Extendedwebbrowser_2并没有触发DocumentCompleted，估计就是这里导致第二次下载时不能触发。
       解决办法：在下载完后，Extendedwebbrowser_2加载空白页"about:blank"，问题解决。
 

下面是IWebBrowserDownloadManager接口完整代码：

Imports Remotion.Dms.Clients.Windows.WebBrowserControl
Imports System.IONamespace MyDownloadmanager                         '定义接口，以实现接口引用 2023.10.27Public Class MyDownloadmanagerImplements IWebBrowserDownloadManagerDim INetCacheFile As String'一些状态的判定（True、False），其中的一种状态（True或False）必须放在接口内进行设定，'不能全部都靠通过外部进程来设定，外部进程只进行其中一种状态的改变就好，否则因为轮询时间差而导致不同步引发非预期结果发生。'例如：AfterLoadBlank#Region "增加属性，将接口的数据传递出去以及传进来"#Region "可读写属性"Private _ContinueDownload As Boolean = TruePublic Property ContinueDownload() As BooleanGetReturn _ContinueDownloadEnd GetSet(ByVal value As Boolean)_ContinueDownload = valueEnd SetEnd PropertyPrivate _DownloadDir As String = ""Public Property DownloadDir() As StringGetReturn _DownloadDirEnd GetSet(ByVal value As String)_DownloadDir = valueEnd SetEnd PropertyPrivate _AttchmentFilename As String = ""Public Property AttchmentFilename() As StringGetReturn _AttchmentFilenameEnd GetSet(ByVal value As String)_AttchmentFilename = valueEnd SetEnd Property'对于会弹出新窗口的下载，因为程序中接管的webbrowser一直没关闭，’在下载完后，需要加载一次新页（在这里加载空白页"about:blank"），‘否则可能无法进行下一次下载。Private _AfterLoadBlank As Boolean = FalsePublic Property AfterLoadBlank() As Boolean    GetReturn _AfterLoadBlankEnd GetSet(ByVal value As Boolean)_AfterLoadBlank = valueEnd SetEnd Property#End Region#Region "ReadOnly Property"Dim _DownloadFileName As String = ""Public ReadOnly Property DownloadFileName() As StringGetReturn _DownloadFileNameEnd GetEnd PropertyPrivate _totalSize As IntegerPublic ReadOnly Property GetTotalSize() As IntegerGetReturn _totalSizeEnd GetEnd PropertyPrivate _currentValue As IntegerPublic ReadOnly Property GetCurrentValue() As IntegerGetReturn _currentValueEnd GetEnd PropertyPrivate _success As BooleanPublic ReadOnly Property GetSuccess() As BooleanGetReturn _successEnd GetEnd PropertyPrivate _statusText As StringPublic ReadOnly Property GetStatusText() As StringGetReturn _statusTextEnd GetEnd PropertyPrivate _isAborted As BooleanPublic ReadOnly Property GetisAborted() As BooleanGetReturn _isAbortedEnd GetEnd PropertyPrivate _IsDownloadCompleted As Boolean = False'下载开始时，设置为false，下载结束或退出时，设置为TruePublic ReadOnly Property IsDownloadCompleted() As Boolean    GetReturn _IsDownloadCompletedEnd GetEnd PropertyPrivate _OnStartDownloading As Boolean = False'下载开始时，设置为false，下载结束或退出时，设置为TruePublic ReadOnly Property OnStartDownloading() As Boolean    GetReturn _OnStartDownloadingEnd GetEnd Property#End Region#End Region#Region "接口函数"Public Sub OnAborted() Implements Remotion.Dms.Clients.Windows.WebBrowserControl.IWebBrowserDownloadManager.OnAbortedWriteRunLog("OnAborted")_isAborted = True_IsDownloadCompleted = True_OnStartDownloading = FalseEnd SubPublic Function OnDataAvailable(ByVal buffer() As Byte, ByVal bytesAvailable As Integer) As Boolean Implements Remotion.Dms.Clients.Windows.WebBrowserControl.IWebBrowserDownloadManager.OnDataAvailable_currentValue += bytesAvailable'需要加这行，否则可能下载时发生阻塞，导致下载中断，而且这种情况与下载文件大小无关，即使很小几M的文件也会发生。Application.DoEvents()      Return _ContinueDownloadEnd Function'在下载完后，需要加载一次新页（在这里加载空白页"about:blank"），否则可能无法进行下一次下载。Public Sub OnDownloadCompleted(ByVal success As Boolean, ByVal statusText As String) Implements Remotion.Dms.Clients.Windows.WebBrowserControl.IWebBrowserDownloadManager.OnDownloadCompleted_isAborted = False_IsDownloadCompleted = True_OnStartDownloading = False_AfterLoadBlank = True_success = success_statusText = statusText_AttchmentFilename = ""WriteRunLog("OnDownloadCompleted：" + success.ToString + "      " + statusText)If success ThenIf String.IsNullOrEmpty(INetCacheFile) ThenWriteRunLog("没有找到IE缓冲区文件！文件 " + _DownloadFileName + " 下载失败！")ElseFile.Copy(INetCacheFile, _DownloadFileName, overwrite:=True)      '从IE缓冲区复制文件WriteRunLog("找到IE缓冲区文件： " + INetCacheFile + "，复制到：" + _DownloadFileName)End IfEnd IfEnd SubPublic Function OnProgress(ByVal currentValue As Integer, ByVal totalSize As Integer, ByVal statusText As String) As Boolean Implements Remotion.Dms.Clients.Windows.WebBrowserControl.IWebBrowserDownloadManager.OnProgress_totalSize = totalSize'从第一次OnProgress中获取下载文件名If String.IsNullOrEmpty(_DownloadFileName) Then      _DownloadFileName = MyGetFileName(statusText)If String.IsNullOrEmpty(_DownloadFileName) Then_DownloadFileName = "TmpFile"End IfIf Directory.Exists(_DownloadDir) Then_DownloadFileName = _DownloadDir + "\" + _DownloadFileNameEnd IfEnd IfIf String.IsNullOrEmpty(INetCacheFile) ThenIf InStr(statusText, "Windows\INetCache") > 0 Then  '查找IE缓冲区文件 保存路径、文件名INetCacheFile = statusText'WriteRunLog("OnProgress找到IE缓冲区文件： " + INetCacheFile)End IfEnd IfSystem.Windows.Forms.Application.DoEvents()Return _ContinueDownloadEnd FunctionPublic Function OnStartDownload(ByVal uri As System.Uri) As Boolean Implements Remotion.Dms.Clients.Windows.WebBrowserControl.IWebBrowserDownloadManager.OnStartDownload_currentValue = 0_OnStartDownloading = True_ContinueDownload = True_IsDownloadCompleted = FalseINetCacheFile = ""_DownloadFileName = ""WriteRunLog("OnStartDownload ：" + uri.ToString)Return TrueEnd Function'OnStartDownload:http://115.1.115.15:9080/FrntMonitor/servlet/com.icbc.cte.cs.servlet.CSReqServlet'1、第一次获得文件名   OnProgress:0 totalSize:0 statusText: C:\Users\gdzs-liyh\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.IE5\0F2VEW6C\statatmdev[2].xls'2、第二次获得下载链接 OnProgress:3483 totalSize:0 statusText:(OnStartDownload中的网址：http://115.1.115.15:9080/FrntMonitor/servlet/com.icbc.cte.cs.servlet.CSReqServlet)'3483就是在这时候读取的数据大小。'OnProgress:3483 totalSize:0 statusText: C:\Users\gdzs-liyh\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.IE5\0F2VEW6C\statatmdev[2].xls'OnDataAvailable:38281  (这个就是文件的实际大小)（可能文件小，此时文件已经下载到缓存：C:\Users\gdzs-liyh\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.IE5\0F2VEW6C\statatmdev[2].xls）'OnProgress:38281 totalSize:0 statusText:(OnStartDownload中的网址)'OnDownloadCompleted'================================='OnStartDownload ：http://115.96.14.11/kjbbs/UpLoadFile/2010-7/20107214401523292.doc'1、第一次获得文件名   OnProgress:0 totalSize:0 statusText ：http://115.96.14.11/kjbbs/UpLoadFile/2010-7/20107214401523292.doc'2、第二次获得下载链接 OnProgress:119296 totalSize:119296 statusText ：http://115.96.14.11/kjbbs/UpLoadFile/2010-7/20107214401523292.doc'OnProgress:119296 totalSize:119296 statusText ：C:\Users\gdzs-liyh\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.IE5\5Q44G40U\20107214401523292.doc'OnProgress:119296 totalSize:119296 statusText ：http://115.96.14.11/kjbbs/UpLoadFile/2010-7/20107214401523292.doc'OnDataAvailable:119296  （可能文件小，此时文件已经下载到缓存：C:\Users\gdzs-liyh\AppData\Local\Microsoft\Windows\Temporary Internet Files\Content.IE5\0F2VEW6C\statatmdev[2].xls）'OnDownloadCompleted#End RegionShared Sub 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 SubPublic Function MyGetFileName(ByVal inStr As String) As String'获取文件名， '文件夹名、文件名不能包含下列字符\/:*?"<>|Dim ss As Stringss = System.IO.Path.GetFileName(inStr)Dim n = InStrRev(ss, "=")If n < ss.Length Thenss = ss.Substring(n)End IfMyGetFileName = ss.Replace("\", "").Replace("/", "").Replace(":", "").Replace("*", "").Replace("?", "").Replace(Chr(34), "").Replace("<", "").Replace(">", "").Replace("|", "")If InStrRev(MyGetFileName, "[") > 1 And InStrRev(MyGetFileName, "[") < InStrRev(MyGetFileName, "]") Then    '将 21018102002617385797[1] 中的 [1] 去掉MyGetFileName = Left(MyGetFileName, InStrRev(MyGetFileName, "[") - 1) + Mid(MyGetFileName, InStrRev(MyGetFileName, "]") + 1)End IfMyGetFileName = _AttchmentFilename + MyGetFileNameEnd FunctionEnd ClassEnd Namespace