Tip 110: Sending a Click Event to a Command Button Control

Abstract
In a Microsoft(r) Visual Basic(r) application, you can simulate a Click =
event to
a Command Button control. This article explains how to send a BN_CLICKED
notification message to a control.

Executing a BN_CLICKED Message
A user who wants to carry out a command in your Microsoft(r) Visual =
Basic(r)
application usually clicks a Command Button control. The code in the =
Command
Button's Click event is then executed.

There may be times, however, when you will want to initiate a Click =
event from
within your Visual Basic program. You can use the Microsoft Windows(r) =
application
programming interface (API) PostMessage function to send a BN_CLICKED =
notification
message to the parent of the Command Button control. This will call the =
button's
Click event.
As you can see from the example program below, the GetDlgCtrlID function
retrieves the Command Button's handle. Next, a call is made to the =
GetParent
function, which retrieves the handle of the window that the Command =
Button resides
on. (In other words, we must retrieve the parent window's handle.)

The last step is to execute a PostMessage function. PostMessage sends a =
BN_CLICKED
notification message to the parent window, which then processes the =
Click event
for the Command Button.
When you run the example program below, the second Command Button's =
Click event
is executed. However, the second Command Button does not receive the =
focusonly its
code is executed.

Example Program
This program shows how to send a Command Button click to the Windows =
operating
system.

1. Create a new project in Visual Basic. Form1 is created by default.
2. Add the following Constant and Declare statements to the General =
Declarations
section of Form1 (note that each Declare statement must be typed as =
a single
line of text):

Const BN_CLICKED =3D 0
Const WM_COMMAND =3D &H111
Private Declare Function GetDlgCtrlID Lib "User" (ByVal hWnd As Integer) =
As
Integer
Private Declare Function GetParent Lib "User" (ByVal hWnd As Integer) As =
Integer
Private Declare Function PostMessage Lib "User" (ByVal hWnd As Integer, =
ByVal
wMsg As Integer, ByVal wParam As Integer, ByVal lParam As Long) As =
Integer

3. Add a Command Button control to Form1. Command1 is created by =
default. Set
its Caption property to "Send".
4. Add the following code to the Click event for Command1:

Private Sub Command1_Click()
ClickButton Command2.hWnd
End Sub

5. Add a second Command Button control to Form1. Command2 is created by =
default.
Set its Caption property to "Receive".
6. Add the following code to the Click event for Command2:

Private Sub Command2_Click()
MsgBox "Command2 was CLICKED!"
End Sub

7. Create a new function called ClickButton. Add the following code to =
this
function:

Sub ClickButton(ByVal hWnd As Integer)
Dim Button As Integer
Dim ParentHwnd As Integer
Dim X As Integer
=20
Button =3D GetDlgCtrlID(hWnd)
ParentHwnd =3D GetParent(hWnd)

X =3D PostMessage(ParentHwnd, WM_COMMAND, Button, BN_CLICKED * =
&H10000 + hWnd)
End Sub

Run the example program by pressing F5. Click the Send Command Button. =
The Click
event for the second Command Button control is immediately executed (the =
message
box is displayed).

Additional References
"BN_CLICKED." (Development Library, Product Documentation, SDKs,
Windows 3.1 SDK, Programmer's Reference Volume 3: Messages, =
Structures)
"GetDlgCtrl." (Development Library, Product Documentation, SDKs,
Windows 3.1 SDK, Programmer's Reference Volume 2: Functions)
PostMessage." (Development Library, Product Documentation, SDKs,
Windows 3.1 SDK, Programmer's Reference Volume 2: Functions)