Using Button Controls (1.2)
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Using Button Controls
The most common way to use button controls is in a dialog window. An
application defines one or more button controls in the dialog template in
the resource file, and processes button messages in the dialog-window
procedure.
Buttons can be associated in groups in dialog windows. A user can move from
one button in a group to another button in the same group by pressing the
ARROW keys. The TAB key moves from one group to the next. Groups are
established by setting the WS_GROUP style bit for the first member of each
group in the dialog template.
You can also use button controls in standard client windows. For these
windows, create a button-control window by calling the WinCreateWindow
function with a window class of WC_BUTTON. Specify the client window as the
owner of the button window. The owner window receives messages from buttons
and can send messages to the buttons to alter their control state. The
control state includes highlighting control text, button position, and the
enabled/disabled state.
Applications can create custom buttons that appear to be controlled by the
application. The BS_USERBUTTON style, used in conjunction with other button
styles, creates a button that notifies the application whenever the button
must be drawn, allowing the application to draw the button.
Buttons in a Dialog Window
Buttons are typically used in dialog windows. An application can define
buttons as part of a dialog-template resource file, as shown in the
following sample Resource Compiler source-code fragment:
DLGTEMPLATE IDD_BUTTON
BEGIN
DIALOG "", 2, 64, 9, 235, 130
BEGIN
AUTORADIOBUTTON "R~adio1", ID_RADIO1, 15, 20, 40, 12, WS_GROUP
AUTORADIOBUTTON "Ra~dio2", ID_RADIO2, 15, 40, 40, 12
AUTORADIOBUTTON "Rad~io3", ID_RADIO3, 15, 60, 40, 12
AUTORADIOBUTTON "R~adio4", ID_RADIO4,15, 80, 40, 12
PUSHBUTTON "Button 1", ID_PUSH1, 100, 50, 14, WS_GROUP
PUSHBUTTON "Button 2", ID_PUSH2, 75, 100, 50, 14, WS_GROUP
PUSHBUTTON "Button 3", ID_PUSH3, 130, 100, 60, 14, WS_GROUP
CHECKBOX "Check Box 1", ID_CHECK1, 150, 20, 58, 12, WS_GROUP
CHECKBOX "no toggle", ID_CHECK2, 150, 40, 58, 12
AUTOCHECKBOX "Check Box 3", ID_CHECK3, 150, 60, 58, 12, WS_GROUP
DEFPUSHBUTTON "OK", DID_OK, 75, 26, 46, 20, WS_GROUP
END
END
Each button item in a dialog window has an ID (for example, ID_RADIO1) that
allows an application to identify the source of the WM_COMMAND and
WM_CONTROL messages. The ID is also used to retrieve the button-window
handle using the WinWindowFromID function.
The dialog template also specifies the text for each button, which is
displayed in a rectangular box. If the button text is too long to fit in the
button, it is clipped to the rectangle. For radio buttons and check boxes,
text is displayed to the right of the button. A user selects the button by
clicking either the button or the text itself.
The WS_GROUP attribute identifies the beginning of each new group of
buttons. In the example above, the first four auto-radio buttons are in the
same group, the following push buttons are in their own group, and the
following two check boxes are in their own group. The auto-radio buttons in
the first group can only be selected one at a time. An application must see
that only one check box in a group is selected at a time. The group can wrap
around from the end of the item list to the beginning.
Notice the DEFPUSHBUTTON style with the DID_OK identification number in the
code fragment above. It is customary to include an OK button with this ID in
most dialog windows to provide a uniform user interface. The DEFPUSHBUTTON
style draws a thick border around a button and allows a user to select the
button by pressing the ENTER key.
The dialog-window procedure for a dialog window containing buttons must
respond to WM_COMMAND and WM_CONTROL messages. A common strategy is to use
auto-radio buttons and auto-check boxes to allow a user to set a list of
attributes for a command, and execute it by choosing the OK button. In this
case, the dialog-window procedure ignores all WM_CONTROL messages that come
from auto-radio buttons and auto-check boxes. These controls select and
deselect themselves. When the dialog-window procedure receives a WM_COMMAND
message for the OK button, it should query the auto-radio buttons and
auto-check boxes to determine which options have been selected before
proceeding with the operation.
Buttons in a Client Window
Applications can also use buttons in non-dialog windows. An application can
create a button window using an application client window as the owner, as
shown in the following code fragment:
/* Create a button window. */
hwndButton = WinCreateWindow(hwndClient, /* parent */
WC_BUTTON, /* class */
"Test Button", /* text */
WS_VISIBLE |
BS_PUSHBUTTON, /* style */
10, 10, /* x, y */
60, 70, /* cx, cy */
hwndClient, /* owner */
HWND_TOP, /* behind */
ID_PBWINDOW, /* id */
NULL, /* control data */
NULL); /* parameters */
Once created in the client window, the button posts a WM_COMMAND message, or
sends a WM_CONTROL message to the client-window procedure. The window
procedure should examine the message ID to determine the button that sent
the message.
Applications that have client-window buttons may move and size the buttons
when the window receives a WM_SIZE message. This message indicates that the
window is changing size. Buttons can be moved and sized using the
WinSetWindowPos function. You can obtain a window handle for a button by
calling the WinWindowFromID function using the parent window and the window
ID for each button.
Responding to a Button-Notification Message
A button control sends a message to its owner window when a user selects the
button, either using the mouse or the keyboard. Buttons created with the
BS_PUSHBUTTON or BS_USERBUTTON styles generate a WM_COMMAND message each
time they are selected (this can be altered by specifying the BS_HELP or
BS_SYSCOMMAND style when the button is created). All other button styles
generate WM_CONTROL messages when selected.
A push button is automatically highlighted when a user selects it using the
mouse. The button tracks the mouse until the user releases the mouse button.
The highlight is turned off if the mouse moves outside the button
boundaries. The push button does not generate any messages to its owner
window until the user releases the mouse button, and then only if the mouse
button is released inside the push-button boundary. When the owner window
receives a WM_COMMAND message from a push button, the low word of the first
parameter in the message contains the button window ID, as specified in the
dialog template or when the button was created.
You should avoid duplicating IDs in menu commands and buttons because they
both send IDs to owner windows as WM_COMMAND messages. However, it is
possible to tell whether a WM_COMMAND message came from a menu or a push
button by looking for the value CMDSRC_PUSHBUTTON or CMDSRC_MENU in the low
word of the second parameter of the message.
Button types other than push buttons generate WM_CONTROL messages when
selected. Applications can examine the low word of the first parameter in
the message to find the button ID and the high word of the first parameter
to determine the notification code for the control message. The notification
code tells the application whether the control message originated from the
user clicking or double clicking, or if the button needs to be drawn.
When a check box or radio button is selected, it sends a WM_CONTROL message
with a notification BN_CLICKED code to the owner window. The owner window
responds by sending a message back to the button to toggle its state.
In the case of auto-check boxes and auto-radio buttons, an application need
not respond because these buttons toggle themselves in response to the
mouse. The application still receives WM_CONTROL messages each time the
button is selected. Most applications that use this default for radio
buttons and check boxes should also use the automatic versions of these
buttons and ignore any WM_COMMAND messages.
Changing the Button State
An application can query and set the highlight and checked state of its
buttons by sending messages to button windows. The window handle for a
button can be obtained by calling the WinWindowFromID function using the
parent window and the window ID of the button. In the case of a dialog
window, the parent would be the dialog window and the ID would be the button
item ID from the dialog template.
Button-window text is stored as window text, and is accessible by using the
WinSetWindowText and WinQueryWindowText functions. The size, position, and
visibility of a button are set using standard window functions.
Owner-Drawn Buttons
An application can create custom buttons by using the BS_USERBUTTON style in
combination with other styles. For example, an application can create a
custom auto-radio button that works like an auto-radio button but whose
appearance is controlled by the application. The owner window receives
WM_CONTROL messages for these buttons whenever they must be drawn,
highlighted, or disabled.
When a button must be drawn, the owner window receives a WM_CONTROL message
with the high word of the first parameter equal to BN_PAINT. The second
parameter is a pointer to a USERBUTTON structure that contains necessary
information the application needs to draw the button.
An application uses the hwnd field in this structure to find the bounding
rectangle for the button. The hps field is used as a presentation space for
any drawing. The high byte of the fsState field contains flags that tell an
application how to draw the button: highlighted, unhighlighted, or disabled.
The high byte of the fsStateOld field contains flags describing the current
highlighted, unhighlighted, or disabled state of the button.
Default Button Behavior
This section describes the messages specifically handled by the predefined
button-control window class.
Message Description
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WM_CREATE Validates the requested button style and sets the
window text.
WM_DESTROY Frees the memory containing the window text.
WM_PAINT Draws the button according to its style and current
state.
WM_SETFOCUS Creates a cursor if receiving the focus, destroys the
cursor if losing the focus.
WM_BUTTON1DOWN Sets mouse capture for the button window.
WM_MOUSEMOVE Sets the default mouse pointer. If the button has the
mouse capture, the button highlight state changes as
the mouse pointer moves in and out of button area.
WM_BUTTON1UP If the button has mouse capture, releases the mouse
capture and sends notification message to the owner
window if the mouse pointer is inside the button when
the mouse button is released. If the button is a
BS_PUSHBUTTON, a WM_COMMAND message is posted,
otherwise a WM_CONTROL message with the BN_CLICKED
code is sent.
WM_BUTTON1DBLCLK Marks the button, sending a BN_DBLCLICKED notification
code when the button-up message arrives.
WM_CHAR Sets mouse capture when the SPACEBAR is pressed,
releases capture when the SPACEBAR is released. Passes
other key messages to the default window procedure.
WM_QUERYDLGCODE Returns DLGC_BUTTON combined using the OR operator
with the appropriate bits to designate the particular
button type.
WM_QUERYWINDOWPARAMS Returns the requested window parameters.
WM_SETWINDOWPARAMS Sets the requested window parameters and redraws the
button, including the cursor, if the window has the
focus.
WM_ENABLE Draws the button.
WM_MATCHMNEMONIC Returns TRUE if mp1 matches a button mnemonic.
BM_QUERYCHECKINDEX Returns the zero-based index to the selected item in
the same group as the button. Returns -1 if no button
in the group is selected or if the button receiving
the message is not a radio button or auto-radio
button.
BM_CLICK Sends a WM_BUTTON1DOWN and WM_BUTTON1UP message to
itself to simulate a user-button selection.
BM_QUERYCHECK Returns the checked state of the button.
BM_SETCHECK Sets the checked state of the button, returns the
previous checked state.
BM_QUERYHILITE Returns the highlight state of the button.
BM_SETHILITE Sets the highlight state of the button, returns the
previous highlight state.
BM_SETDEFAULT Sets the default button state, redraws the button.
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