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

June 12, 1995

Abstract

In a Microsoft® Visual Basic® 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® Visual Basic® 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® 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 focus—only 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 = 0
   Const WM_COMMAND = &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
       
       Button = GetDlgCtrlID(hWnd)
       ParentHwnd = GetParent(hWnd)
       X = 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." (MSDN Library Archive, Product Documentation, SDKs, Windows 3.1 SDK, Programmer's Reference Volume 3: Messages, Structures)

"GetDlgCtrl." (MSDN Library Archive, Product Documentation, SDKs, Windows 3.1 SDK, Programmer's Reference Volume 2: Functions)

”PostMessage." (MSDN Library Archive, Product Documentation, SDKs, Windows 3.1 SDK, Programmer's Reference Volume 2: Functions)