该方法不需要使用API及第三方控件

这里使用的是VB的UserControl控件的AsyncRead方法

步骤如下:

1、添加一个用户控件，设置InvisibleAtRuntime属性为true，目的是运行时该控件不显示用户界面，就象Timer控件一样。

2、到自定义控件的代码窗口，添加如下代码

Option Explicit '下载结果枚举 Public Enum DownloadResults eSUCCESS = 0 '下载成功 eCONNECTERROR = 1 '连接<a href="https://www.jb51.cc/tag/cuowu/" target="_blank" class="keywords">错误</a> eTRANSFERERROR = 2 '数据传输<a href="https://www.jb51.cc/tag/cuowu/" target="_blank" class="keywords">错误</a> eWRITEERROR = 3 '保存本地<a href="https://www.jb51.cc/tag/cuowu/" target="_blank" class="keywords">错误</a> eUserStop = 4 '中止 End Enum '下载进度事件 Identifier-下载标识,RecvdBytes-已下载字节数,MaxBytes-总字节数,PassTimer-已用下载时间(秒) Public Event DownloadProgress(Identifier As String,RecvdBytes As Long,MaxBytes As Long,PassTimer As Long) '下载完成事件 Identifier-下载标识,ccDownloadResults-下载结果,PassTimer-已用下载时间(秒) Public Event DownloadComplete(Identifier As String,Result As DownloadResults,PassTimer As Long) Dim FstrURL As String 'FTP 下载字符串,含IP,端口号,<a href="https://www.jb51.cc/tag/yonghuming/" target="_blank" class="keywords">用户名</a>,密码,下载的<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>及其路径 Dim FstrSaveFile As String '下载的<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>保存在本地的<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>名及其路径 Dim FstrIdentifier As String '下载标识 Dim FlngStart As Long '开始下载时间 '下载<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a> 'strURL FTP 下载字符串,下载的<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>及其路径 ' 形如 ftp://<a href="https://www.jb51.cc/tag/yonghuming/" target="_blank" class="keywords">用户名</a>:密码@FTP地址/目录/<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a> 'strSaveFile 保存时的本地<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>名 'strIdentifier 下载标识,可以同时下载多个<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a>,依据此字符串区别所下载的<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a> Public Sub DownLoad(ByVal strURL As String,ByVal strSaveFile As String,ByVal strIdentifier As String) On Error GoTo ERRHAND FstrURL = strURL FstrSaveFile = strSaveFile FstrIdentifier = strIdentifier FlngStart = Timer UserControl.AsyncRead strURL,vbAsyncTypeByteArray,strIdentifier,vbAsyncReadForceUpdate Exit Sub ERRHAND: RaiseEvent DownloadComplete(strIdentifier,eCONNECTERROR,Timer - FlngStart) End Sub Private Sub UserControl_AsyncReadComplete(AsyncProp As AsyncProperty) On Error GoTo Errs Dim F() As Byte Dim fn As Long Dim sFile As String Dim s As String sFile = FstrSaveFile With AsyncProp s = .PropertyName If .BytesMax <> 0 Then If .BytesMax <> .BytesRead Then On Error Resume Next UserControl.CancelAsyncRead s RaiseEvent DownloadComplete(s,eTRANSFERERROR,Timer - FlngStart) '---- 传输<a href="https://www.jb51.cc/tag/cuowu/" target="_blank" class="keywords">错误</a>,下载失败 Else '//Call to DoEvents updates transfer status on frmMain '..for large files before file processing begins. DoEvents fn = FreeFile F = .Value Open sFile For Binary Access Write As #fn '--------- Open file for writing Put #fn,F '-------------------------------------- Put downloaded data to file Close #fn Erase F '------------------------------------------- Purge Array fn = FileLen(sFile) If Dir$(sFile,39) <> "" Then '--------------------- Verify write completed RaiseEvent DownloadComplete(s,eSUCCESS,Timer - FlngStart) Else On Error Resume Next UserControl.CancelAsyncRead s RaiseEvent DownloadComplete(s,eWRITEERROR,Timer - FlngStart) '--- Completed but <a href="https://www.jb51.cc/tag/Failed/" target="_blank" class="keywords">Failed</a> to write to disk End If End If Else On Error Resume Next '---------------------------------- ReVive never connected to the file or server UserControl.CancelAsyncRead s RaiseEvent DownloadComplete(s,Timer - FlngStart) End If End With Errs_Exit: Exit Sub Errs: If Err.Number = 7 Then '内存溢出 RaiseEvent DownloadComplete(s,Timer - FlngStart) ElseIf Err.Number = 75 Then '打开<a href="https://www.jb51.cc/tag/wenjian/" target="_blank" class="keywords">文件</a><a href="https://www.jb51.cc/tag/cuowu/" target="_blank" class="keywords">错误</a> RaiseEvent DownloadComplete(s,Timer - FlngStart) Else RaiseEvent DownloadComplete(s,Timer - FlngStart) End If Resume Errs_Exit End Sub Private Sub UserControl_AsyncReadProgress(AsyncProp As AsyncProperty) On Error GoTo Errs With AsyncProp If .BytesMax <> 0 Then RaiseEvent DownloadProgress(.PropertyName,CLng(.BytesRead),CLng(.BytesMax),Timer - FlngStart) End If End With Exit Sub Errs: RaiseEvent DownloadComplete(AsyncProp.PropertyName,Timer - FlngStart) End Sub '中止下载 'strIdentifier 下载标识 Public Sub StopDown(ByVal strIdentifier As String) On Error GoTo Errs UserControl.CancelAsyncRead strIdentifier Exit Sub Errs: End Sub

3、测试。在一个FORM中放一个刚才定义的控件，放一个Label，放一个CommandButton，均取默认值，到FORM的代码窗口添加如下代码

Option Explicit Private Sub Command1_Click() Call UserControl11.DownLoad("ftp://anonymous:kkk@ftp.microsoft.com/developr/visualstu<a href="https://www.jb51.cc/tag/dio/" target="_blank" class="keywords">dio</a>/sp3/full/vssp3_1.exe","d:/test.rar","abc") End Sub Private Sub UserControl11_DownloadComplete(Identifier As String,PassTimer As Long) Label1.Caption = "下载完成总共用时" & CStr(PassTimer) & "秒." End Sub Private Sub UserControl11_DownloadProgress(Identifier As String,PassTimer As Long) Label1.Caption = "正在下载" & Format(RecvdBytes / MaxBytes,"0.00%") DoEvents End Sub

可以参考MSDN中关于UserControl.AsyncRead方法的说明

该方法的缺点是不能上传文件，不能获取FTP上文件列表等。可以配合相关API函数进行操作

如果进行http下载，形如 http://文件连接