How to send a CBN_SELCHANGE message when using CB_SETCURSEL ?

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

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 2

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());

}