GetWindowLong Function

Declare Function GetWindowLong Lib "user32.dll" Alias "GetWindowLongA" (ByVal hWnd As Long, ByVal nIndex As Long) As Long

Platforms

Windows 95: Supported.
Windows 98: Supported.
Windows NT: Requires Windows NT 3.1 or later.
Windows 2000: Supported.
Windows CE: Requires Windows CE 1.0 or later.

Description & Usage

GetWindowLong retrieves a 32-bit value from the information about a window. This function can also read a 32-bit value from the block of extra memory given to the window, if one exists.

Return Value

If an error occured, the function returns 0 (use GetLastError to get the error code). If successful, the function returns the 32-bit value which was retrieved.

Visual Basic-Specific Issues

None.

Parameters

hWnd

A handle to the window to retrieve a 32-bit value from.

nIndex

To get a 32-bit value from the window's extra memory block, this is the zero-based offset of the byte to begin reading from. Valid values range from 0 to the size of the extra memory block in bytes minus four. To get a 32-bit value from the properties of the window, this is one of the following flags specifying which piece of information to retieve:

GWL_EXSTYLE: Retrieve the extended window styles of the window.
GWL_HINSTANCE: Retrieve a handle to the owning application's instance.
GWL_HWNDPARENT: Retrieve a handle to the parent window, if any.
GWL_ID: Retrieve the identifier of the window.
GWL_USERDATA: Retrieve the application-defined 32-bit value associated with the window.
GWL_STYLE: Retrieve the window styles of the window.
GWL_WNDPROC: Retrieve a pointer to the WindowProc hook function acting as the window's procedure.

If the window happens to be a dialog box, this could also be one of the following flags:

DWL_DLGPROC: Retrieve a handle to the WindowProc hook function acting as the dialog box procedure.
DWL_MSGRESULT: Retrieve the return value of the last message processed by the dialog box.
DWL_USER: Retrieve the application-defined 32-bit value associated with the dialog box.

Constant Definitions

Const GWL_EXSTYLE = -20
Const GWL_HINSTANCE = -6
Const GWL_HWNDPARENT = -8
Const GWL_ID = -12
Const GWL_STYLE = -16
Const GWL_USERDATA = -21
Const GWL_WNDPROC = -4
Const DWL_DLGPROC = 4
Const DWL_MSGRESULT = 0
Const DWL_USER = 8

Example

When the user clicks button Command1, determine if its parent window has a maximize button or not by checking its window style. To use this example, you must first place a command button named Command1 on a form window.

' This code is licensed according to the terms and conditions listed here.

' Declarations and such needed for the example:
' (Copy them to the (declarations) section of a module.)
Public Declare Function GetWindowLong Lib "user32.dll" Alias "GetWindowLongA" (ByVal hWnd As Long, _
	ByVal nIndex As Long) As Long
Public Const GWL_STYLE = -16
Public Const WS_MAXIMIZEBOX = &H10000

' *** Place the following code inside a form window. ***

Private Sub Command1_Click ()
	Dim styles As Long  ' receives window styles of Form1
	
	' Get the window styles of Form1.
	styles = GetWindowLong(Me.hWnd, GWL_STYLE)
	' Determine if a maximize box exists or not.
	If (styles And WS_MAXIMIZEBOX) = WS_MAXIMIZEBOX Then
		Debug.Print "The form window has a maximize box."
	Else
		Debug.Print "The form window does not have a maximize box."
	End If
End Sub