问题
I have a base64 string which was generated from an image using another application. Now on my application I want to convert the base64 string to byte and display it on a PictureBox.
I already found a sample application which takes a byte input and sets a PictureBox image. Unfortunately the sample application gets the byte array from an image and just translates it back. Here's the function it uses.
Public Function PictureFromByteStream(b() As Byte) As IPicture
Dim LowerBound As Long
Dim ByteCount As Long
Dim hMem As Long
Dim lpMem As Long
Dim IID_IPicture(15)
Dim istm As stdole.IUnknown
On Error GoTo Err_Init
If UBound(b, 1) < 0 Then
Exit Function
End If
LowerBound = LBound(b)
ByteCount = (UBound(b) - LowerBound) + 1
hMem = GlobalAlloc(&H2, ByteCount)
If hMem <> 0 Then
lpMem = GlobalLock(hMem)
If lpMem <> 0 Then
MoveMemory ByVal lpMem, b(LowerBound), ByteCount
Call GlobalUnlock(hMem)
If CreateStreamOnHGlobal(hMem, 1, istm) = 0 Then
If CLSIDFromString(StrPtr("{7BF80980-BF32-101A-8BBB-00AA00300CAB}"), IID_IPicture(0)) = 0 Then
Call OleLoadPicture(ByVal ObjPtr(istm), ByteCount, 0, IID_IPicture(0), PictureFromByteStream)
End If
End If
End If
End If
Exit Function
Err_Init:
If Err.Number = 9 Then
'Uninitialized array
MsgBox "You must pass a non-empty byte array to this function!"
Else
MsgBox Err.Number & " - " & Err.Description
End If
End Function
Here's the function I found to convert a base64 string to a byte, it seems to be converting it but when I pass the byte data to the above function, no image appears.
Private Function DecodeBase64(ByVal strData As String) As Byte()
Dim objXML As MSXML2.DOMDocument
Dim objNode As MSXML2.IXMLDOMElement
' help from MSXML
Set objXML = New MSXML2.DOMDocument
Set objNode = objXML.createElement("b64")
objNode.dataType = "bin.base64"
objNode.Text = strData
DecodeBase64 = objNode.nodeTypedValue
' thanks, bye
Set objNode = Nothing
Set objXML = Nothing
End Function
And here's my code calling the functions.
Dim b() As Byte
b = DecodeBase64(Text1.Text)
Dim pic As StdPicture
Set pic = PictureFromByteStream(b)
Set Picture1.Picture = pic
回答1:
Try this:
Option Explicit
Private Const CRYPT_STRING_BASE64 As Long = &H1&
Private Const STRING_IPICTURE_GUID As String = "{7BF80980-BF32-101A-8BBB-00AA00300CAB}"
Private Declare Function CryptStringToBinaryW Lib "Crypt32.dll" ( _
ByVal pszString As Long, _
ByVal cchString As Long, _
ByVal dwFlags As Long, _
ByVal pbBinary As Long, _
ByRef pcbBinary As Long, _
ByVal pdwSkip As Long, _
ByVal pdwFlags As Long) As Long
Private Declare Function CreateStreamOnHGlobal Lib "ole32.dll" ( _
ByRef hGlobal As Any, _
ByVal fDeleteOnResume As Long, _
ByRef ppstr As Any) As Long
Private Declare Function OleLoadPicture Lib "olepro32.dll" ( _
ByVal lpStream As IUnknown, _
ByVal lSize As Long, _
ByVal fRunMode As Long, _
ByRef riid As GUID, _
ByRef lplpObj As Any) As Long
Private Declare Function CLSIDFromString Lib "ole32.dll" ( _
ByVal lpsz As Long, _
ByRef pclsid As GUID) As Long
Type GUID
Data1 As Long
Data2 As Integer
Data3 As Integer
Data4(7) As Byte
End Type
Public Function DecodeBase64(ByVal strData As String) As Byte()
Dim Buffer() As Byte
Dim dwBinaryBytes As Long
dwBinaryBytes = LenB(strData)
ReDim Buffer(dwBinaryBytes - 1) As Byte
If CryptStringToBinaryW(StrPtr(strData), LenB(strData), CRYPT_STRING_BASE64, _
VarPtr(Buffer(0)), dwBinaryBytes, 0, 0) Then
ReDim Preserve Buffer(dwBinaryBytes - 1) As Byte
DecodeBase64 = Buffer
End If
Erase Buffer
End Function
Public Function PictureFromByteStream(ByRef b() As Byte) As IPicture
On Error GoTo errorHandler
Dim istrm As IUnknown
Dim tGuid As GUID
If Not CreateStreamOnHGlobal(b(LBound(b)), False, istrm) Then
CLSIDFromString StrPtr(STRING_IPICTURE_GUID), tGuid
OleLoadPicture istrm, UBound(b) - LBound(b) + 1, False, tGuid, PictureFromByteStream
End If
Set istrm = Nothing
Exit Function
errorHandler:
Debug.Print "Error in converting to IPicture."
End Function
来源：https://stackoverflow.com/questions/43040177/base64-string-to-byte-to-image