This article was previously published under Q168204
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Microsoft Visual Basic for Windows can use the Microsoft Windows APISendMessage function to close any active window that has a system menu(referred to as the Control Box within Visual Basic for Windows) with theClose option.
This sample program uses the Windows API SendMessage function to post amessage to any window in the environment, provided the handle to the windowis known. The API FindWindow function is used to determine the handleassociated with the window the user wants to close. To use FindWindow, youmust know either the ClassName or the Caption (if any) of that window.Please see the REFERENCES section below for more information.
Steps to Create Example Program
Start Visual Basic and select Standard EXE. If Visual Basic is already running, click New Project on the File menu and select Standard EXE. Form1 is created by default.
Create two Command Buttons called Command1 and Command2.
On the Project menu, click Add Module (ALT, P, M). Module1 is created by default.
In the Declarations section, declare the following two API functions:
Declare Function FindWindow _ Lib "user32" Alias "FindWindowA" _ (ByVal lpClassName As String, _ ByVal lpWindowName As String) _ As Long Declare Function SendMessage _ Lib "user32" Alias "SendMessageA" _ (ByVal hwnd As Long, _ ByVal wMsg As Long, _ ByVal wParam As Long, _ lParam As Long) _ As Long
Within the Command1 Click event, add the following code:
Private Sub Command1_Click() Shell "Calc.exe", vbNormalFocus End Sub
Within the Command2 Click event, add the following code:
Private Sub Command2_Click() Dim lpClassName As String Dim lpCaption As String Dim Handle As Long Const NILL = 0& Const WM_SYSCOMMAND = &H112 Const SC_CLOSE = &HF060& lpClassName = "SciCalc" lpCaption = "Calculator" '* Determine the handle to the Calculator window. Handle = FindWindow(lpClassName$, lpCaption$) '* Post a message to Calc to end its existence. Handle = SendMessage(Handle, WM_SYSCOMMAND, SC_CLOSE, NILL) End Sub
On the Run menu, click Start or press the F5 key to start the program. Clicking the Command1 button starts a (new) instance of the Windows Calculator accessory. Clicking on the Command2 button kills an instance of the Calculator.
For more information on the FindWindow and SendMessage functions, query onthe following words in the Microsoft Knowledge Base:
FindWindow and Visual Basic or SendMessage and Visual Basic
For information on a different sample application that returns assortedinformation for a windowed application, please see the following article inthe Microsoft Knowledge Base:
112649 : How to Get a Window's Class Name and Other Window Attributes