Can I programmatically do drag-and-drop from my local file system to a 3rd party application?

Question

Hello!

I have a VB .NET WPF that searches a local directory structure to locate a few hundred files per month. These files need to be filed (drag and dropped) onto a 3rd party application that stores the files. The third party application has its own directory structure, and so the correct directory has to be picked before each file is dragged-and-dropped.

I am able to control the 3rd party program with SENDMESSAGEs. I can log in, select the correct directory, and read all the values from the 3rd party controls.

To manually do the upload, the user drags the file to the 3rd party control (which happens to be a ListView) and then the file gets copied to the 3rd party's file system.

Can I somehow simulate the drag-and-drop function after selecting the correct location in the 3rd party application? I tried WM_DROPFILES, but that didn't appear to do anything. However, I tried the same WM_DROPFILES into Notepad and it didn't do anything, either.

I found the Control.DoDragDrop method to initiate the drag-and-drop, but could not find a message to send to the 3rd party application to start the "drop" part of the process.

Thanks for any help!

Accepted Answer

From comments, a translation of C++ code which works with native DoDragDrop API (Control.DoDragDrop does not seem to work well)
To be adapted/improved =>
(I had to remove an 'e' from Sleep or I could not post ...)

'Does not seem to work fine....
'Dim filesList As System.Collections.Specialized.StringCollection = New System.Collections.Specialized.StringCollection()
'filesList.Add("E:	est.txt")
'filesList.Add("E:\hulk.jpg")
'Dim dataObject As DataObject = New DataObject()
'dataObject.SetData(DataFormats.FileDrop, filesList)
'dataObject.SetFileDropList(filesList)

OleInitialize(IntPtr.Zero)

' Test with 2 files, in a same directory for pidlParent
Dim pItemIDL1 As IntPtr = ILCreateFromPath("E:	est.txt")
Dim pItemIDL2 As IntPtr = ILCreateFromPath("E:\hulk.jpg")
'Dim pItemIDL2 As IntPtr = ILCreateFromPath("E:	est2.txt")
Dim arrayPidl = New IntPtr(255) {}
Dim pidlParent As IntPtr = IntPtr.Zero, pidlItem As IntPtr = IntPtr.Zero

Dim nPidlNumber As Integer = 0
pidlItem = ILFindLastID(pItemIDL1)
arrayPidl(0) = ILClone(pidlItem)
nPidlNumber += 1
ILRemoveLastID(pItemIDL1)
pidlParent = ILClone(pItemIDL1)
ILFree(pItemIDL1)

pidlItem = ILFindLastID(pItemIDL2)
arrayPidl(1) = ILClone(pidlItem)
nPidlNumber += 1
ILRemoveLastID(pItemIDL2)
'pidlParent = ILClone(pItemIDL2)
ILFree(pItemIDL2)

Dim pDataObject As System.Runtime.InteropServices.ComTypes.IDataObject = Nothing
Dim hr As HRESULT = SHCreateFileDataObject(pidlParent, nPidlNumber, arrayPidl, Nothing, pDataObject)
If (hr = HRESULT.S_OK) Then
    ' Test with an IDropTarget app with window title = "Drop Target"
    Dim hWndDest As IntPtr = FindWindow(Nothing, "Drop Target")
    ' Notepad only works with 1 file
    'Dim hWndDest As IntPtr = FindWindow("Notepad", Nothing)
    If (hWndDest <> IntPtr.Zero) Then
        SwitchToThisWindow(hWndDest, True)
        System.Threading.Thread.Slep(500)
        Dim rcDest As New RECT()
        GetWindowRect(hWndDest, rcDest)

        ' Move mouse cursor in the middle of the window
        Dim nX As Integer = (rcDest.left + (rcDest.right - rcDest.left) / 2) * 65535 / GetSystemMetrics(SM_CXSCREEN)
        Dim nY As Integer = (rcDest.top + (rcDest.bottom - rcDest.top) / 2) * 65535 / GetSystemMetrics(SM_CYSCREEN)

        Dim mi() As INPUT = New INPUT(2) {}
        mi(0).type = INPUT_MOUSE
        mi(0).union.mi.dx = nX
        mi(0).union.mi.dy = nY
        mi(0).union.mi.dwFlags = MOUSEEVENTF_ABSOLUTE Or MOUSEEVENTF_MOVE
        'mi(1).union.mi.dwFlags = MOUSEEVENTF_LEFTDOWN
        mi(1).union.mi.dwFlags = MOUSEEVENTF_LEFTUP
        'mi(2).union.mi.dwFlags = MOUSEEVENTF_LEFTUP
        'SendInput(3, mi, Marshal.SizeOf(mi(0)))
        SendInput(2, mi, Marshal.SizeOf(mi(0)))

        Dim pDropSource As CDropSource = New CDropSource()
        Dim dwEffectDragDrop As UInteger = DragDropEffects.None
        hr = OleDoDragDrop(pDataObject, pDropSource, DragDropEffects.Link Or DragDropEffects.Copy, dwEffectDragDrop)

        Marshal.ReleaseComObject(pDataObject)
       'Dim dde As System.Windows.Forms.DragDropEffects = Me.DoDragDrop(dataObject, DragDropEffects.Copy Or DragDropEffects.Link)
      End If
End If

with declarations :

Public Enum HRESULT As Integer
    S_OK = 0
    S_FALSE = 1
    E_NOINTERFACE = &H80004002
    E_NOTIMPL = &H80004001
    E_FAIL = &H80004005
    E_UNEXPECTED = &H8000FFFF
    E_OUTOFMEMORY = &H8007000E
    DRAGDROP_S_CANCEL = &H40101
    DRAGDROP_S_DROP = &H40100
    DRAGDROP_S_USEDEFAULTCURSORS = &H40102
End Enum


Public Shared Function FindWindow(ByVal lpClassName As String, ByVal lpWindowName As String) As IntPtr
End Function


Public Shared Function SwitchToThisWindow(hWnd As IntPtr, fAltTab As Boolean) As Boolean
End Function


Public Shared Function GetSystemMetrics(ByVal nIndex As Integer) As Integer
End Function

Public Const SM_CXSCREEN As Integer = 0
Public Const SM_CYSCREEN As Integer = 1
Public Const SM_XVIRTUALSCREEN As Integer = 76
Public Const SM_YVIRTUALSCREEN As Integer = 77
Public Const SM_CXVIRTUALSCREEN As Integer = 78
Public Const SM_CYVIRTUALSCREEN As Integer = 79

Public Const MOUSEEVENTF_MOVE As Integer = &H1
Public Const MOUSEEVENTF_LEFTDOWN As Integer = &H2
Public Const MOUSEEVENTF_LEFTUP As Integer = &H4
Public Const MOUSEEVENTF_ABSOLUTE As Integer = &H8000


Public Structure MOUSEINPUT
    Public dx As Integer
    Public dy As Integer
    Public mouseData As Integer
    Public dwFlags As Integer
    Public time As Integer
    Public dwExtraInfo As IntPtr
End Structure


Public Structure KEYBDINPUT
    Public wVk As Short
    Public wScan As Short
    Public dwFlags As Integer
    Public time As Integer
    Public dwExtraInfo As IntPtr
End Structure


Public Structure INPUT
    Public type As Integer
    Public union As INPUTUNION
End Structure


Public Structure INPUTUNION
    
    Public mi As MOUSEINPUT
    
    Public ki As KEYBDINPUT
    '
    'Public hi As HARDWAREINPUT
End Structure

Public Const INPUT_MOUSE As Integer = 0
Public Const INPUT_KEYBOARD As Integer = 1


Public Shared Function SendInput(ByVal nInputs As Integer,  ByVal pInputs() As INPUT, ByVal cbSize As Integer) As Integer
End Function


Public Structure RECT
    Public left As Integer
    Public top As Integer
    Public right As Integer
    Public bottom As Integer
    Public Sub New(
              left As Integer,
              top As Integer,
              right As Integer,
              bottom As Integer)
        Me.left = left
        Me.top = top
        Me.right = right
        Me.bottom = bottom
    End Sub
End Structure


Public Shared Function GetWindowRect(hWnd As IntPtr, ByRef lpRect As RECT) As Boolean
End Function


Public Shared Function ILCreateFromPath(pszPath As String) As IntPtr
End Function


Public Shared Function SHCreateFileDataObject(ByVal pidlFolder As IntPtr, ByVal cidl As UInteger, ByVal apidl As IntPtr(), ByVal pdtInner As System.Runtime.InteropServices.ComTypes.IDataObject,  ByRef ppdtobj As System.Runtime.InteropServices.ComTypes.IDataObject) As HRESULT
End Function


Public Shared Function ILFindLastID(pidl As IntPtr) As IntPtr
End Function


Public Shared Function ILClone(ByVal pidl As IntPtr) As IntPtr
End Function


Public Shared Function ILRemoveLastID(ByVal pidl As IntPtr) As Boolean
End Function


Public Shared Sub ILFree(pidl As IntPtr)
End Sub


Public Shared Function OleInitialize(ByVal pvReserved As IntPtr) As HRESULT
End Function


Public Shared Function OleDoDragDrop( pDataObj As System.Runtime.InteropServices.ComTypes.IDataObject,  pDropSource As IDropSource, dwOKEffects As UInteger, ByRef pdwEffect As UInteger) As HRESULT
End Function


Public Interface IDropSource
    
    Function QueryContinueDrag( fEscapePressed As Boolean, grfKeyState As UInteger) As HRESULT
    
    Function GiveFeedback(dwEffect As UInteger) As HRESULT
End Interface

Public Class CDropSource
    Implements IDropSource
    Private Function QueryContinueDrag(fEscapePressed As Boolean, grfKeyState As UInteger) As HRESULT Implements IDropSource.QueryContinueDrag
        If fEscapePressed Then
            Return HRESULT.DRAGDROP_S_CANCEL
        End If
        If Not (grfKeyState And MK_LBUTTON) Then
            Console.Beep(9000, 10) 'for test
            Return HRESULT.DRAGDROP_S_DROP
        End If
        Return HRESULT.S_OK
    End Function

    Public Function GiveFeedback(dwEffect As UInteger) As HRESULT Implements IDropSource.GiveFeedback
        Return HRESULT.DRAGDROP_S_USEDEFAULTCURSORS
    End Function
End Class

Public Const MK_LBUTTON = &H1
Public Const MK_RBUTTON = &H2
Public Const MK_SHIFT = &H4
Public Const MK_CONTROL = &H8
Public Const MK_MBUTTON = &H10
Public Const MK_XBUTTON1 = &H20
Public Const MK_XBUTTON2 = &H40

Can I programmatically do drag-and-drop from my local file system to a 3rd party application?

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