CONTROL ADD CHECKBOX statement

Purpose

Add an auto-checkbox to a dialog. This is typically used to indicate a True/False or on/off selection, and is common in dialogs that offer choices of options to a user.

Syntax

CONTROL ADD CHECKBOX, hDlg, id&, txt$, x, y, xx, yy [, [style&] [, [exstyle&]]] [[,] CALL callback]

hDlg

Handle of the dialog in which the checkbox will be created. The dialog will become the parent of the control.

id&

Unique identifier for the control in the range 1 to 65535, frequently specified with numeric equates for clarity of the code. For example, the equate %DisableUser is more informative than a literal value such as 497. Best practice suggests identifiers should start at 100 to avoid conflict with any of the standard predefined identifiers.

txt$

Text to be displayed next to the checkbox. An ampersand (&) may be included in txt$ to specify a hot-key. See the Remarks section below.

x, y

Integer expressions, variables, or numeric literal values, specifying the location of the control inside the dialog client area. x is the horizontal position, and y is the vertical position. 0,0 refers to the upper left corner of the dialog box client area. Coordinates are specified in the same terms (pixels or dialog units) as the parent dialog.

Integer expression, variable, or numeric literal value, specifying the width of the control. The width is given in the same terms (pixels or dialog units) as the parent dialog. The most common value used in the Microsoft Dialog Editor and Visual Studio is 40 dialog units.

Integer expression, variable, or numeric literal value, specifying the height of the control. The height is given in the same terms (pixels or dialog units) as the parent dialog. The most common value used in the Microsoft Dialog Editor and Visual Studio is 14 dialog units.

style&

Primary style of the checkbox control. The default checkbox style comprises %BS_LEFT, %BS_VCENTER, and %WS_TABSTOP. The default style is used only if both the primary and extended parameters are omitted from the statement. For example:

CONTROL ADD CHECKBOX, hDlg, id&, txt$, 100, 100, 40, 14, , , _

CALL CheckboxCallback() ' Use default styles

Custom style values replace the default values. That is, they are not additional to the default style values - your code must specify all necessary primary and extended style parameters.

The primary checkbox style value can be a combination of any values below, combined together with the OR operator to form a bitmask:

%BS_BOTTOM	Place the text at the bottom of the control.
%BS_CENTER	Center the text horizontally in the control.
%BS_LEFT	Place the text on the left side of the label portion of the control. Also see %BS_LEFTTEXT. (default)
%BS_LEFTTEXT	Place the checkbox to the right of the text portion of the control. Combine with %BS_RIGHT to right-align text against the left side of the checkbox control.
%BS_MULTILINE	Wrap the caption text across multiple lines, if the text string is too long to fit on a single line. To force a wrap, insert a $CR (or $CRLF) into the caption text at the desired wrap position.
%BS_NOTIFY	Enable a control to send the %BN_KILLFOCUS and %BN_SETFOCUS messages to the callback.
%BS_PUSHLIKE	Button state alternates (toggles) between normal (raised) and depressed (sunken) modes.
%BS_RIGHT	Place the text on the right side of the label portion of the control. Also see %BS_LEFTTEXT.
%BS_TOP	Place the text at the top of the control.
%BS_VCENTER	Center the text vertically in the control. (default)
%WS_DISABLED	Create a control that is initially disabled. A disabled control cannot receive input from the user.
%WS_GROUP	Define the start of a group of controls. The first control in each group should also use %WS_TABSTOP style. The next %WS_GROUP control in the tab order defines the end of this group and the start of a new group. Groups configured this way permit the arrow keys to shift focus between the controls within the group, and focus can jump from group to group with the usual TAB and SHIFT+TAB keys. Both tab stops and groups are permitted to wrap from the end of the tab order back to the start.
%WS_TABSTOP	Allow checkbox control to receive the keyboard focus when the user presses the TAB and SHIFT+TAB keys. Pressing the TAB key changes the keyboard focus to the next control with the %WS_TABSTOP style, and SHIFT+TAB moves it to the previous control with %WS_TABSTOP. (default)

exstyle&

Extended style of the checkbox control. The default extended checkbox style comprises %WS_EX_LEFT. The default extended style is used if both the primary and extended parameters are omitted from the CONTROL ADD CHECKBOX statement, in the same manner as style& above.

The extended checkbox style value can be a combination of any values below, combined together with the OR operator to form a bitmask:

%WS_EX_CLIENTEDGE	Apply a sunken edge border to the control.
%WS_EX_LEFT	The control has generic "left-aligned" properties. (default)
%WS_EX_RIGHT	The control has generic "right-aligned" properties. This style has an effect only if the shell language is Hebrew, Arabic, or another language that supports reading order alignment; otherwise, the style is ignored.
%WS_EX_STATICEDGE	Apply a three-dimensional border style to the control (intended to be used for items that do not accept user input).
%WS_EX_TRANSPARENT	Controls/windows beneath the control are drawn before the control is drawn. The control is deemed transparent because elements behind the control have already been painted - the control itself is not drawn differently. True transparency is achieved by using Regions - see MSDN for more information.
%WS_EX_WINDOWEDGE	Apply a raised edge border to the control.

callback

Optional statement to designate the name of a Callback Function to handle all %WM_COMMAND messages for the control. If a callback for the control is not designated, you must create a Callback Function for the dialog to process notification messages from your checkbox.

In general, when the control Callback Function processes a message, it should return TRUE (non-zero) to prevent the message being passed unnecessarily to the dialog callback (if one exists). The dialog callback should also return TRUE if the notification message is processed by that Callback Function. Otherwise, the DDT engine processes unhandled messages.

Remarks

If the ampersand (&) character appears in the txt$ parameter, the letter that follows will be displayed underscored. This adds a control accelerator (hot-key) to enable the user to directly "click" a control, simply by pressing and holding the ALT key while pressing the specified hot-key. For example, "O&ption " makes ALT+p the hot-key.

When the user clicks a control, a message is sent to the Callback Function designated for the control. If there is no Callback Function designated, the message is sent to the callback for the dialog.

If the control callback processes the notification message, it should return TRUE (non-zero) to prevent the message being passed needlessly to the dialog callback, and eventually to the DDT engine itself.

Notification messages are sent to the Callback Function, with CBMSG = %WM_COMMAND, CBCTL holding the ID (id&) of the control, and CBCTLMSG holding the following values:

%BN_CLICKED	Sent when the user clicks a mouse button or activates the control with the hot-key (unless the control has been disabled).
%BN_DISABLE	Sent when a control is disabled.
%BN_KILLFOCUS	Sent when a control loses the keyboard focus. The control must include the %BS_NOTIFY style.
%BN_SETFOCUS	Sent when a control receives the keyboard focus. The control must include the %BS_NOTIFY style.

When a Callback Function receives a %WM_COMMAND message, it should explicitly test the value of CBCTL and CBCTLMSG to guarantee it is responding appropriately to the notification message.