Sua aplicação pode precisar baixar um arquivo da web, esta é uma tarefa fácil de concluir.
O código abaixo usa a função de API URLDownloadToFile do Windows para executar o download real. O algoritmo deste artigo manipula essa API é uma função chamada DownloadFile, e manipula as circunstâncias em que o arquivo de destino local já existe.
O protótipo da função de DownloadFile é como se segue:
Public Function DownloadFile(UrlFileName As String, _
DestinationFileName As String, _
Overwrite As DownloadFileDisposition, _
ErrorText As String) As Boolean
Option Explicit
Option Compare Text
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' modDownloadFile
' By Chip Pearson, chip@cpearson.com, www.cpearson.com/Excel/DownloadFile.aspx
' Date: 23-April-2003
' This module contains the DownloadFile function and supporting players to
' download a file from a URL to a local file name.
'
' Example Usage:
'
' Dim URL As String
' Dim LocalFileName As String
' Dim B As Boolean
' Dim ErrorText As String
'
' URL = "http://www.cpearson.com/Zips/FindAll.zip"
' LocalFileName = "C:\Test\FindAll.zip"
' B = DownloadFile(UrlFileName:=URL, _
' DestinationFileName:=LocalFileName, _
' Overwrite:=OverwriteRecycle, _
' ErrorText:=ErrorText)
' If B = True Then
' Debug.Print "Download successful"
' Else
' Debug.Print "Download unsuccessful: " & ErrorText
' End If
'
' The Overwrite parameter of DownloadFile indicates how to handle the
' case when LocalFileName already exists. It is one of the following
' values:
' OverwriteKill use Kill to delete the existing file.
' OverwriteRecycle send the existing file to the Recycle Bin.
' DoNotOverwrite do not overwrite and terminate the procedure.
' PromptUser prompt the user asking whether to overwrite file.
'
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Public Enum DownloadFileDisposition
OverwriteKill = 0
OverwriteRecycle = 1
DoNotOverwrite = 2
PromptUser = 3
End Enum
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' Windows API functions, constants,and types.
' Used for RecycleFile.
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Private Declare Function SHFileOperation Lib "shell32.dll" Alias _
"SHFileOperationA" (lpFileOp As SHFILEOPSTRUCT) As Long
Private Declare Function PathIsNetworkPath Lib "shlwapi.dll" _
Alias "PathIsNetworkPathA" ( _
ByVal pszPath As String) As Long
Private Declare Function GetSystemDirectory Lib "kernel32" _
Alias "GetSystemDirectoryA" ( _
ByVal lpBuffer As String, _
ByVal nSize As Long) As Long
Private Declare Function SHEmptyRecycleBin _
Lib "shell32" Alias "SHEmptyRecycleBinA" _
(ByVal hwnd As Long, _
ByVal pszRootPath As String, _
ByVal dwFlags As Long) As Long
Private Const FO_DELETE = &H3
Private Const FOF_ALLOWUNDO = &H40
Private Const FOF_NOCONFIRMATION = &H10
Private Const MAX_PATH As Long = 260
Private Type SHFILEOPSTRUCT
hwnd As Long
wFunc As Long
pFrom As String
pTo As String
fFlags As Integer
fAnyOperationsAborted As Boolean
hNameMappings As Long
lpszProgressTitle As String
End Type
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' Download API function.
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Private Declare Function URLDownloadToFile Lib "urlmon" Alias _
"URLDownloadToFileA" ( _
ByVal pCaller As Long, _
ByVal szURL As String, _
ByVal szFileName As String, _
ByVal dwReserved As Long, _
ByVal lpfnCB As Long) As Long
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' DownloadFile
' This downloads a file from a URL to a local filename.
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Public Function DownloadFile(UrlFileName As String, _
DestinationFileName As String, _
Overwrite As DownloadFileDisposition, _
ErrorText As String) As Boolean
Dim Disp As DownloadFileDisposition
Dim Res As VbMsgBoxResult
Dim B As Boolean
Dim S As String
Dim L As Long
ErrorText = vbNullString
If Dir(DestinationFileName, vbNormal) <> vbNullString Then
Select Case Overwrite
Case OverwriteKill
On Error Resume Next
Err.Clear
Kill DestinationFileName
If Err.Number <> 0 Then
ErrorText = "Error Kill'ing file '" & DestinationFileName & "'." & vbCrLf & Err.Description
DownloadFile = False
Exit Function
End If
Case OverwriteRecycle
On Error Resume Next
Err.Clear
B = RecycleFileOrFolder(DestinationFileName)
If B = False Then
ErrorText = "Error Recycle'ing file '" & DestinationFileName & "." & vbCrLf & Err.Description
DownloadFile = False
Exit Function
End If
Case DoNotOverwrite
DownloadFile = False
ErrorText = "File '" & DestinationFileName & "' exists and disposition is set to DoNotOverwrite."
Exit Function
'Case PromptUser
Case Else
S = "The destination file '" & DestinationFileName & "' already exists." & vbCrLf & _
"Do you want to overwrite the existing file?"
Res = MsgBox(S, vbYesNo, "Download File")
If Res = vbNo Then
ErrorText = "User selected not to overwrite existing file."
DownloadFile = False
Exit Function
End If
B = RecycleFileOrFolder(DestinationFileName)
If B = False Then
ErrorText = "Error Recycle'ing file '" & DestinationFileName & "." & vbCrLf & Err.Description
DownloadFile = False
Exit Function
End If
End Select
End If
L = URLDownloadToFile(0&, UrlFileName, DestinationFileName, 0&, 0&)
If L = 0 Then
DownloadFile = True
Else
ErrorText = "Buffer length invalid or not enough memory."
DownloadFile = False
End If
End Function
Private Function RecycleFileOrFolder(FileSpec As String) As Boolean
Dim FileOperation As SHFILEOPSTRUCT
Dim lReturn As Long
If (Dir(FileSpec, vbNormal) = vbNullString) And _
(Dir(FileSpec, vbDirectory) = vbNullString) Then
RecycleFileOrFolder = True
Exit Function
End If
With FileOperation
.wFunc = FO_DELETE
.pFrom = FileSpec
.fFlags = FOF_ALLOWUNDO
' Or
.fFlags = FOF_ALLOWUNDO + FOF_NOCONFIRMATION
End With
lReturn = SHFileOperation(FileOperation)
If lReturn = 0 Then
RecycleFileOrFolder = True
Else
RecycleFileOrFolder = False
End If
End Function
