Graphics Reference
In-Depth Information
The key issue here is that we need to determine when the mouse has left the button.
However, tracking the mouse all the time throughout the entire window is processor-
intensive, so you don't want to do that; we want to limit mouse tracking as much as
possible. To accomplish this, add an
NSTrackingArea
to the
contentView
when the
mouseDown
event is received, and we limit this
NSTrackingArea
to the rectangle containing
the button that was pressed.
The
AppDelegate
is set within the
NSTrackingArea
as the owner of the area, which tells
the area to notify
AppDelegate
whenever the mouse enters or exits the rectangle, but only
when we are the active application. We also tell
NSTrackingArea
to assume it is starting
within the rectangle so that the first event we receive is when the mouse exits.
In addition to adding an
NSTrackingArea
, we also keep a pointer to the button that was
pressed. This pointer is used in other methods to turn the selection of the button on and
off and to properly handle the
mouseUp
event.
This addition to the
-mouseDown:
method causes two other methods to be called:
-mouseExited:
and
-mouseEntered:
; both are defined in Listing 11-12.
LISTING 11-12
AppDelegate -mouseExited: Implementation
- (
void
)mouseExited:(
NSEvent
*)theEvent
{
[
selectedButton setSelected
:
NO
];
}
- (
void
)mouseEntered:(
NSEvent
*)theEvent
{
[
selectedButton setSelected
:
YES
];
}
After adding these methods, the button that was pressed selects and unselects as the
mouse enters and exits its rectangle. This gives the user visual feedback while the mouse
button is down so that they know the button click can still be canceled.
LISTING 11-13
AppDelegate -mouseUp: Implementation
- (
void
)mouseUp:(
NSEvent
*)theEvent;
{
if
(!
selectedButton
)
return
;
[[
window contentView
]
removeTrackingArea
:
buttonDownTrackingArea
];
[
selectedButton setSelected
:
NO
];
LZButtonLayer
*hitLayer = [
self
buttonLayerHit
];
if
(hitLayer !=
selectedButton
) {
selectedButton
=
nil
;
return
;
}
