If App.PrevInstance Then
     Unload Me
End If

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" 
(ByVal hwnd As Long, ByVal wMsg As Long, 
ByVal wParam As Long, lParam As Any) As Long

ret = SendMessage(Main.hwnd, wMsg, wParam, ByVal CStr(Command))

If App.PrevInstance Then
  ' FindWindow on the other instance
  ' SendMessage with WM_COPYDATA the filename
    End
  Else
    Dim frm As New Form1
    Set frm = New Form1
    frm.Show
  End If
End Sub

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" 
(ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" 
(ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Public Sub Main()
    Dim m_hWnd As Long
    m_hWnd = FindWindow(vbNullString, "Image Viewer")

    If App.PrevInstance = True Then
        ret = SendMessage(m_hWnd, WM_COPYDATA, -1, ByVal CStr(Command))
        MsgBox ret & " " & WM_COPYDATA
        End
    Else
        Load MainW
        MainW.Show
    End If
End Sub

Dim cData As COPYDATASTRUCT
  Dim Buffer(MAX_PATH) As Byte               ' buffer large enough to handle the max path plus null terminator

  RtlMoveMemory Buffer(0), ByVal Command$, MAX_PATH
  cData.dwData = 0  ' this long variable could be used for security
  cData.cbData = Len(Command$) + 1
  cData.lpData = VarPtr(Buffer(0))
  SendMessage PreviousInstancehWnd, WM_COPYDATA, Me.hWnd, cData

Private Declare Function FindWindow Lib "user32" Alias "FindWindowA" (ByVal lpClassName As String, ByVal lpWindowName As String) As Long

Private Declare Function SetForegroundWindow Lib "user32" (ByVal hWnd As Long) As Long

Private Declare Function IsIconic Lib "user32" (ByVal hWnd As Long) As Long

Private Declare Function ShowWindow Lib "user32" (ByVal hWnd As Long, ByVal nCmdShow As Long) As Long

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Private Const WM_COPYDATA = &H4A
Private Const SW_RESTORE = 9

Private Type COPYDATASTRUCT
    dwData As Long
    cbData As Long
    lpData As Long
End Type

Public Sub Main()
    
    If App.PrevInstance = True Then
    
        'MsgBox "previnst=true"
        
        Dim hWnd As Long
        Dim cds As COPYDATASTRUCT
        hWnd = FindWindow(vbNullString, "Image Viewer")
        
        If hWnd Then
        
            'MsgBox "found window"
            
            If IsIconic(hWnd) Then
                MsgBox "X"
                Call ShowWindow(hWnd, SW_RESTORE)
            End If
            Call SetForegroundWindow(hWnd)
        Else
            Exit Sub
        End If
        cds.cbData = LenB(Command)
        cds.lpData = StrPtr(Command)
        Call SendMessage(hWnd, WM_COPYDATA, hWnd, cds)
        End
    Else
        Load MainW
        MainW.Show
    End If
End Sub

Private Type COPYDATASTRUCT
    dwData As Long
    cbData As Long
    lpData As Long
End Type

Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long

Const LB_FINDSTRING = &H18F
Private Const WM_COPYDATA = &H4A

Dim pic(100) As String
Dim num As Integer

Private Sub About_Click()
    frmAbout.Show
End Sub

Private Sub Exit_Click()
    End
End Sub

Private Sub Form_Load()

    Dim NewHeight As Double, NewWidth As Double
    Img.Stretch = False
    Img.Visible = False
    pic(num) = Command
    
    
    Img.Picture = LoadPicture(pic(num))
    
    NewWidth = Me.ScaleWidth / Img.Width
    NewHeight = (Me.ScaleHeight - 24.981) / Img.Height
    ratio = Img.Width / Img.Height
    If NewWidth < 1 Or NewHeight < 1 Then
        
        Img.Stretch = True
        
        If NewWidth < NewHeight Then
            Img.Width = Img.Width * NewWidth
            Img.Height = Img.Height * NewWidth
        Else
            Img.Width = Img.Width * NewHeight
            Img.Height = Img.Height * NewHeight
        End If
    End If

    Img.Move (Me.ScaleWidth - Img.Width) / 2, ((Me.ScaleHeight - Img.Height) / 2) + 24.981
    Img.Visible = True
    num = num + 1
End Sub

Private Sub Msghook_Message(ByVal Msg As Long, ByVal wp As Long, ByVal lp As Long, result As Long)
    Dim cds As COPYDATASTRUCT
    Dim Send As String
        If Msg = WM_COPYDATA Then
        'copymem cds, ByVal lp, Len(cds)
        Send = Space$(cds.cbData \ 2)
        'copymem ByVal StrPtr(Send), ByVal cds.lpData, cds.cbData
        result = True
    End If
End Sub