The Be Book - System Overview - The Interface Kit
A BButton
object draws a labeled button on-screen and responds when the
button is clicked or when it's operated from the keyboard. If the
BButton
is the default button for its window and the window is the active window,
the user can operate it by pressing the Enter key.
BButtons
have a single state. Unlike check boxes and radio buttons, the
user can't toggle a button on and off. However, the button's value
changes while it's being operated. During a click (while the user holds
the mouse button down and the cursor points to the button on-screen), the
BButton's
value is set to 1 (B_CONTROL_ON). Otherwise, the value is 0
(B_CONTROL_OFF).
This class depends on the control framework defined in the
BControl
class. In particular, it calls these
BControl functions:
SetValue()
to make each change in the
BControl's
value. This is a
hook function that you can override to take collateral action when the
value changes.
Invoke()
to post a message each time the button is clicked or
operated from the keyboard. You can designate the object that should
handle the message by calling
BControl's
SetTarget()
function inherited from BInvoker.
A model for the message is set by the
BButton constructor (or by
BControl's
SetMessage()
function inherited from BInvoker).
IsEnabled()
to determine how the button should be drawn and whether
it's enabled to post a message. You can call
BControl's
SetEnabled()
to enable and disable the button.
A BButton
is an appropriate control device for initiating an action. Use a
BCheckBox, a
BPictureButton, or
BRadioButtons
to set a state.
