GetClassLong Function

Declare Function GetClassLong Lib "user32.dll" Alias "GetClassLongA" (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

GetClassLong retrieves a single 32-bit value from the information about the window class to which the specified window belongs. The class's properties may not necessarily match perfectly with the actual properties of the window. This function can also retrieve a 32-bit value from the extra memory area associated with the window class.

Return Value

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

Visual Basic-Specific Issues

None.

Parameters

hWnd

A handle to a window which belongs to the class to read a property of.

nIndex

To retrieve a 32-bit value from the class's extra memory, set this to the zero-based offset of the byte to begin reading at. Valid values are 0 to the number of bytes of extra memory minus 4, inclusive. To retrieve a 32-bit property of the class, set this to one of the following flags specifying which 32-bit value to retrieve from the window class:

GCW_ATOM: Retrieve the atom which identifies the window class.
GCL_CBCLSEXTRA: Retrieve the size in bytes of the extra memory associated with the window class.
GCL_CBWNDEXTRA: Retrieve the size in bytes of the extra memory associated with each window belonging to the window class.
GCL_HBRBACKGROUND: Retrieve a handle to the brush used to paint the backgrounds of windows belonging to the class.
GCL_HCURSOR: Retrieve a handle to the cursor associated with the class.
GCL_HICON: Retrieve a handle to the icon associated with the class.
GCL_HICONSM: Retrieve a handle to the small icon associated with the class.
GCL_HMODULE: Retrieve a handle to the module which registered the class.
GCL_MENUNAME: Retrieve a pointer to the string identifying the name of the menu resource associated with the class.
GCL_STYLE: Retrieve the window styles associated with the class.
GCL_WNDPROC: Retrieve a pointer to the WindowProc hook function which acts as the window procedure for windows belonging to the window class.

Constant Definitions

Const GCW_ATOM = -32
Const GCL_CBCLSEXTRA = -20
Const GCL_CBWNDEXTRA = -18
Const GCL_HBRBACKGROUND = -10
Const GCL_HCURSOR = -12
Const GCL_HICON = -14
Const GCL_HMODULE = -16
Const GCL_MENUNAME = -8
Const GCL_STYLE = -26
Const GCL_WNDPROC = -24

Example

' Draw the icon associated with whatever class window Form1
' belongs to.  Draw the icon on Form1.  This icon is not necessarily the
' same icon which Form1 uses, but it can be.
Dim hIcon As Long  ' handle to the class's icon
Dim retval As Long  ' return value

' Retrieve a handle to the class's icon.
hIcon = GetClassLong(Form1.hWnd, GWL_HICON)  ' this gets the class's icon, not the window's
' Draw that icon at coordinate (0,0) on Form1.
retval = DrawIcon(Form1.hDC, 0, 0, hIcon)

Related Functions

GetWindowLong, SetClassLong