User Interaction - Core Animation - page 186

LISTING 11-9 AppDelegate -mouseDown: Implementation

- ( void )mouseDown:( NSEvent *)theEvent;
{

[[ self buttonLayerHit ] setSelected : YES ];

}

When the mouseDown event is received, we want to tell the selected button that it is
selected and have it change its appearance. Because the -buttonLayerHit method returns
only LZButtonLayer or nil , we can safely nest its call within the -setSelected: call, as
shown in Listing 11-10.

LISTING 11-10 AppDelegate -mouseUp: Implementation

- ( void )mouseUp:( NSEvent *)theEvent;
{

LZButtonLayer *hitLayer = [ self buttonLayerHit ];
[hitLayer setSelected : NO ];
[ colorBar setBackgroundColor :[hitLayer myColor ]];

}

Watching the Mouse
Playing with this initial version shows a few issues right away. If the mouse button is
pressed over the LZButtonLayer and released while off of it, the button stays selected.
Worse, if one button is pressed and released on another, the second button's color is
selected while the first button stays selected!

To fix these issues, we need to refine the mouseUp and mouseDown methods, as shown in
Listing 11-11.

LISTING 11-11 Updated AppDelegate -mouseDown: Implementation

- ( void )mouseDown:( NSEvent *)theEvent;
{

LZButtonLayer *layer = [ self buttonLayerHit ];
if (!layer) return ;
selectedButton = layer;
[ selectedButton setSelected : YES ];
NSRect buttonRect = NSRectFromCGRect ([ selectedButton frame ]);
buttonDownTrackingArea = [[ NSTrackingArea alloc ] initWithRect :buttonRect
options :( NSTrackingMouseEnteredAndExited | NSTrackingActiveInActiveApp |
NSTrackingEnabledDuringMouseDrag | NSTrackingAssumeInside ) owner : self
userInfo : nil ];
[[ window contentView ] addTrackingArea : buttonDownTrackingArea ];

}