(VB)FTP異步下載

 該方法不需要使用API及第三方控件

這裏使用的是VB的UserControl控件的AsyncRead方法

 

步驟如下:

1、添加一個用戶控件，設置InvisibleAtRuntime屬性爲true，目的是運行時該控件不顯示用戶界面，就象Timer控件一樣。

2、到自定義控件的代碼窗口，添加如下代碼

Option Explicit '下載結果枚舉 Public Enum DownloadResults eSUCCESS = 0 '下載成功 eCONNECTERROR = 1 '連接錯誤 eTRANSFERERROR = 2 '數據傳輸錯誤 eWRITEERROR = 3 '保存本地錯誤 eUserStop = 4 '中止 End Enum '下載進度事件 Identifier-下載標識,RecvdBytes-已下載字節數,MaxBytes-總字節數,PassTimer-已用下載時間(秒) Public Event DownloadProgress(Identifier As String, RecvdBytes As Long, MaxBytes As Long, PassTimer As Long) '下載完成事件 Identifier-下載標識,ccDownloadResults-下載結果,PassTimer-已用下載時間(秒) Public Event DownloadComplete(Identifier As String, Result As DownloadResults, PassTimer As Long) Dim FstrURL As String 'FTP 下載字符串,含IP,端口號,用戶名,密碼,下載的文件及其路徑 Dim FstrSaveFile As String '下載的文件保存在本地的文件名及其路徑 Dim FstrIdentifier As String '下載標識 Dim FlngStart As Long '開始下載時間 '下載文件 'strURL FTP 下載字符串,含IP,端口號,用戶名,密碼,下載的文件及其路徑 ' 形如 ftp://用戶名:密碼@FTP地址/目錄/文件 'strSaveFile 保存時的本地文件名 'strIdentifier 下載標識,可以同時下載多個文件,依據此字符串區別所下載的文件 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) '---- 傳輸錯誤,下載失敗 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 failed 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, eCONNECTERROR, Timer - FlngStart) End If End With Errs_Exit: Exit Sub Errs: If Err.Number = 7 Then '內存溢出 RaiseEvent DownloadComplete(s, eCONNECTERROR, Timer - FlngStart) ElseIf Err.Number = 75 Then '打開文件錯誤 RaiseEvent DownloadComplete(s, eWRITEERROR, Timer - FlngStart) Else RaiseEvent DownloadComplete(s, eCONNECTERROR, 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, eCONNECTERROR, Timer - FlngStart) End Sub '中止下載 'strIdentifier 下載標識 Public Sub StopDown(ByVal strIdentifier As String) On Error GoTo Errs UserControl.CancelAsyncRead strIdentifier Exit Sub Errs: End Sub

 

3、測試。在一個FORM中放一個剛纔定義的控件，放一個Label，放一個CommandButton，均取默認值，到FORM的代碼窗口添加如下代碼

Option Explicit Private Sub Command1_Click() Call UserControl11.DownLoad("ftp://anonymous:[e-mail]/developr/visualstudio/sp3/full/vssp3_1.exe", "d:/test.rar", "abc") End Sub Private Sub UserControl11_DownloadComplete(Identifier As String, Result As DownloadResults, PassTimer As Long) Label1.Caption = "下載完成總共用時" & CStr(PassTimer) & "秒." End Sub Private Sub UserControl11_DownloadProgress(Identifier As String, RecvdBytes As Long, MaxBytes As Long, PassTimer As Long) Label1.Caption = "正在下載" & Format(RecvdBytes / MaxBytes, "0.00%") DoEvents End Sub

 

可以參考MSDN中關於UserControl.AsyncRead方法的說明

該方法的缺點是不能上傳文件，不能獲取FTP上文件列表等。可以配合相關API函數進行操作

如果進行http下載，形如 http://文件連接