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VBA Tips - Fazendo o download de um arquivo - Downloading A File From The Web

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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
' 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
'
'        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.
''''''''''''''''''''''''''''''''''''''
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


Tags: VBA, download, URL, Web,file

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