How to change combo box selected value of another application? Visual Basic - vb.net

Question

I know how to click a button of another application using the codes below. But now I need to know how to change the selected value of a combo box.
'Declaration
Private Declare Auto Function FindWindow Lib "user32.dll" (ByVal lpClassName As String, ByVal lpWindowName As String) As IntPtr
Private Declare Auto Function FindWindowEx Lib "user32.dll" (ByVal hWndParent As IntPtr, ByVal hWndChildAfter As IntPtr, ByVal lpszClass As String, ByVal lpszWindow As String) As IntPtr
Declare Auto Function PostMessage Lib "user32.dll" (ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As IntPtr, ByRef lParam As IntPtr) As IntPtr
Private Const BM_CLICK = &HF5
'Usage
Dim ButtonHandle As IntPtr
Dim MainWindowHandle As IntPtr
MainWindowHandle = FindWindow(FormClass, FormCaption)
ButtonHandle = FindWindowEx(MainWindowHandle, IntPtr.Zero, TargetClass, TargetCaption)
If ButtonHandle <> 0 Then
PostMessage(ButtonHandle, BM_CLICK, 0, 0)
End If
All I need to do is to change the combobox selected value of a different application from its default value of Off to a value of On. Any help is very much appreciated. Thank You.

Answer 1

Finally I now know how to do this. The code that I used is shown below.
'Declaration
Private Declare Auto Function FindWindow Lib "user32.dll" (ByVal lpClassName As String, ByVal lpWindowName As String) As IntPtr
Private Declare Auto Function FindWindowEx Lib "user32.dll" (ByVal hWndParent As IntPtr, ByVal hWndChildAfter As IntPtr, ByVal lpszClass As String, ByVal lpszWindow As String) As IntPtr
Declare Auto Function PostMessage Lib "user32.dll" (ByVal hWnd As IntPtr, ByVal Msg As Integer, ByVal wParam As IntPtr, ByRef lParam As IntPtr) As IntPtr
Private Const BM_CLICK = &HF5
Private Const CB_SETCURSEL = &H14E
'Usage
Dim MainWindowHandle As IntPtr
Dim ChildAfter As IntPtr
Dim ComboBoxHandle As IntPtr
'Get the Handle
MainWindowHandle = FindWindow(FormClass, FormCaption)
'Get the ChildAfter of the Combo Box
ChildAfter = FindWindowEx(MainWindowHandle, IntPtr.Zero, ChildClass, ChildCaption)
'Get the handle of the combobox dropdown
ComboBoxHandle = FindWindowEx(MainWindowHandle, ChildAfter, "ComboBox", vbNullString)
'Select combo box index(1)
PostMessage(ComboBoxHandle, CB_SETCURSEL, 1, 0)
From the MSDN documentation of FindWindowEx:
hwndChildAfter [in, optional]
Type: HWND
A handle to a child window. The search begins with the next child window in the Z order. The child window must be a direct child window of hwndParent, not just a descendant window.
If hwndChildAfter is NULL, the search begins with the first child window of hwndParent.
#RemyLebeau Thank you so much for helping me do this.