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

' 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.
'
Public Enum DownloadFileDisposition
    OverwriteKill = 0
    OverwriteRecycle = 1
    DoNotOverwrite = 2
    PromptUser = 3
End Enum

'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' Windows API functions, constants,and types.
' Used for RecycleFile.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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

'''''''''''''''''''''''''''
' 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



''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
' DownloadFile
' This downloads a file from a URL to a local filename.
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
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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