Windows API Guide - Reference - Volume 1: Version 3.0 For the MS-DOS and PC-DOS Operating Systems

2017-07-07 02:10:07

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_SETCHECK message to a button changes the checked state of a button. Naturally, the button has to be either a check box or a radio button for the message to work. The message can check or uncheck the button. If the button is a three-state check box, the message can also put the button into its third, grayed state.

Return Value

The BM_SETCHECK message always returns 0.

Visual Basic-Specific Issues

None.

Parameters

wParam

One of the following flags specifying how to set the button's checked state:

BST_CHECKED: Check the button.
BST_INDETERMINATE: Put the button into its third, grayed state. This only works for three-state check boxes.
BST_UNCHECKED: Uncheck the button.

lParam

Not used -- set to 0.

Constant Definitions

Const BM_SETCHECK = &HF1 Const BST_CHECKED = &1 Const BST_INDETERMINATE = &2 Const BST_UNCHECKED = &0

Example

Use the BM_SETCHECK message to place a check mark inside of Check1. Do this when a button is pressed. To run this example, place a check box control named Check1 and a command button named Command1 inside 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 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_SETCHECK = &HF1 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 retval As Long ' return value ' Place a check mark inside Check1. retval = SendMessage(Check1.hWnd, BM_SETCHECK, ByVal CLng(BST_CHECKED), ByVal CLng(0)) ' That's it! End Sub