Anyone knows why a SendMessage/DTM_SETSYSTEMTIME fails across processes?[when the message is send from one process to the Date Time picker control in a different process, SendMessage returns 0 - indicating an error - and the picker remains unaffected]

Following is the code I had used to send

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

Private Declare Function FindWindowEx Lib "user32" Alias "FindWindowExA" (ByVal hWnd1 As Long, ByVal hWnd2 As Long, ByVal lpsz1 As String, ByVal lpsz2 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 Long) As Long

Private Declare Function GetLastError Lib "kernel32" () As Long

Private Const DTM_GETSYSTEMTIME = &H1001
Private Const DTM_SETSYSTEMTIME = &H1002
Private Const DTM_SETFORMAT = &H1032


Private Const GDT_VALID = 0
Private Type SYSTEMTIME
wYear As Integer
wMonth As Integer
wDayOfWeek As Integer
wDay As Integer
wHour As Integer
wMinute As Integer
wSecond As Integer
wMilliseconds As Integer
End Type

Private Sub Command1_Click()
Dim lngwhnd As Long
Dim lngwhnd_DTPick As Long
Dim lngErr As Long
Dim objSYS1 As SYSTEMTIME
Dim objSYS As SYSTEMTIME
Dim lngptr As Long

Dim str As String
objSYS.wYear = Year(Now) - 1
objSYS.wMonth = Month(Now) - 1
objSYS.wDay = Day(Now) - 1

lngwhnd = FindWindow(vbNullString, "DTPick")
lngwhnd_DTPick = FindWindowEx(lngwhnd, 0, "DTPicker20WndClass", vbNullString)

lngErr = SendMessage(lngwhnd_DTPick, DTM_GETSYSTEMTIME, GDT_VALID, objSYS)

lngErr = GetLastError

End Sub

I was able to set the date in the same process using the above code.

Also tried sending the LPARAM as pointer to the system date structure using the VarPtr function !! it didt work

FindWindowEx internally calls GetWinfowText to retrieve the name of the window if the control is in the same process, if however the control belongs to some other process GetWinfowText retreivs only the caption of the window if any otherwise it returns NULL in which case there's nothing to compare the window name with. So make sure that u are able to find the window name and thus getting the window handle correctly before trying to send the control any messages.


Regards
Ankur Verma