Windows API Guide: Concepts in the Windows API

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

Sending the BM_GETCHECK message to a button determines if that button is currently checked. Obviously, this message only works with buttons that are check boxes or radio boxes.

Return Value

If an error occured, the message returns zero. Otherwise, the message returns one of the following values specifying the button's checked state:

BST_CHECKED: The button is checked.
BST_INDETERMINATE: The button is grayed, in an indeterminate state. This only works with check boxes that have three possible states.
BST_UNCHECKED: The button is unchecked.

Visual Basic-Specific Issues

None.

Parameters

wParam: Not used -- set to 0.
lParam: Not used -- set to 0.

Constant Definitions

Const BM_GETCHECK = &HF0 Const BST_CHECKED = &1 Const BST_INDETERMINATE = &2 Const BST_UNCHECKED = &0

Example

Use the BM_GETCHECK message to determine the checked status of check box Check1 when a button is pressed. To run this example, you need to create a check box control named Check1 and a command button named Command1 in a form window. The check box may be any type you wish.

' 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 SendMessage Lib "user32.dll" Alias "SendMessageA" (ByVal hWnd _ As Long, ByVal Msg As Long, wParam As Any, lParam As Any) As Long Public Const BM_GETCHECK = &HF0 Public Const BST_CHECKED = &1 Public Const BST_INDETERMINATE = &2 Public Const BST_UNCHECKED = &0 ' *** Place the following code inside the form window. *** Private Sub Command1_Click() Dim state As Long  ' checked state of the check box ' Find the checked state of Check1 and tell the user what it is. state = SendMessage(Check1.hWnd, BM_GETCHECK, ByVal CLng(0), ByVal CLng(0)) Select Case state Case BST_CHECKED Debug.Print "The check box is checked." Case BST_INDETERMINATE Debug.Print "The check box is in its third state (grayed)." Case BST_UNCHECKED Debug.Print "The check box is not checked." End Select End Sub