How to send a CBN_SELCHANGE message when using CB_SETCURSEL? - c++

Question

When using the CB_SETCURSEL message, the CBN_SELCHANGE message is not sent.
How to notify a control that the selection was changed ?
P.S.
I found on the Sexchange site, a very ugly hack :
SendMessage( hwnd, 0x014F/*CB_SHOWDROPDOWN*/, 1, 0 );
SendMessage( hwnd, 0x014E/*CB_SETCURSEL*/, ItemIndex, 0 );
SendMessage( hwnd, 0x0201/*WM_LBUTTONDOWN*/, 0, -1 );
SendMessage( hwnd, 0x0202/*WM_LBUTTONUP*/, 0, -1 );
Will do for now... Not really.
P.S.2
For resolving my problem, I'll follow Ken's suggestion in the comments.

Answer 1

This might help the next person out:
[DllImport("User32.dll", EntryPoint = "SendMessage")]
private static extern int SendMessage(IntPtr hwnd, int msg, int wParam, int lParam);
[DllImport("user32.dll", EntryPoint = "GetWindowLong")]
private static extern IntPtr GetWindowLongPtr32(IntPtr hWnd, int nIndex);
[DllImport("user32.dll", EntryPoint = "GetWindowLongPtr")]
private static extern IntPtr GetWindowLongPtr64(IntPtr hWnd, int nIndex);
public static IntPtr GetWindowLongPtr(IntPtr hWnd, int nIndex)
{
if (IntPtr.Size == 8)
return GetWindowLongPtr64(hWnd, nIndex);
else
return GetWindowLongPtr32(hWnd, nIndex);
}
static int MakeWParam(int loWord, int hiWord)
{
return (loWord & 0xFFFF) + ((hiWord & 0xFFFF) << 16);
}
public const int CB_SETCURSEL = 0x014E;
public const int CBN_SELCHANGE = 0x0001;
public enum GWL
{
GWL_WNDPROC = (-4),
GWL_HINSTANCE = (-6),
GWL_HWNDPARENT = (-8),
GWL_STYLE = (-16),
GWL_EXSTYLE = (-20),
GWL_USERDATA = (-21),
GWL_ID = (-12)
}
public static IntPtr Hwnd_select_control_parent = IntPtr.Zero;
public static IntPtr Hwnd_select_control = IntPtr.Zero;
static void changeit()
{
// Google WinSpy for tips on how to figure out how to get window handles from known ctrl_id
Hwnd_select_control = 14298; // or whatever the handle of the combo box is
// Get the parent of the selectbox control
Hwnd_select_control_parent = GetWindowLongPtr(service_window_control, (int)GWL.GWL_HWNDPARENT);
// Get the control id of the selectbox if you don't already have it
IntPtr nID = GetWindowLongPtr(Hwnd_select_control, (int)GWL.GWL_ID);
int ctrl_id = nID.ToInt32();
// Change the combo box to the value "My Value"
SendMessage(Hwnd_select_control, CB_SETCURSEL, "My Value", null);
// low ID is the ctrl_id of the combo box, high id is CBN_SELCHANGE
int send_cbn_selchange = MakeWParam(ctrl_id, CBN_SELCHANGE);
// Send the WM_COMMAND to the parent, not the control itself
SendMessage(Hwnd_serviceselect_control_parent, 0x111 /* WM_COMMAND */, send_cbn_selchange, Hwnd_serviceselect_control.ToInt32());
}

Answer 2

You're not supposed to use CBN_SELCHANGE unless the change in selection was made by the user.
You don't indicate what language you're using; it would make it easier to provide you with a workaround if you did so.
In Delphi, where an OnChange() would be associated with the combobox, you just call the event method directly:
// Send the CB_SETCURSEL message to the combobox
PostMessage(ComboBox1.Handle, CB_SETCURSEL, Whatever, WhateverElse);
// Directly call the OnChange() handler, which is the equivalent to CBN_SELCHANGE
ComboBox1Change(nil);

Answer 3

I just discovered calling these SendMessages to the Combobox twice works... I know it's not perfect but it worked for me. (Written in VB6)
For looper = 1 To 2
bVal = SendMessage(inHandle, COMBO.CB_SHOWDROPDOWN, True, 0)
count = SendMessage(inHandle, COMBO.CB_SETCURSEL, 1, 0)
count = SendMessage(inHandle, WIND.WM_LBUTTONDOWN, 0, -1)
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