User Interaction - Core Animation - page 178

input and needs to determine how to process that input. Before diving into the meat of
figuring out how to receive events, we first need to create a custom NSView that receives
mouse events and hands them off to a delegate object, as shown in Listing 11-1.

LISTING 11-1 LZContentView Header for Receiving Mouse Events

#import <Cocoa/Cocoa.h>

@interface LZContentView : NSView
{

IBOutlet id delegate ;

}

@end

The header subclasses NSView adds one instance variable (or ivar) to the object; the dele-
gate . Because this delegate is assigned in Interface Builder, it is flagged as an IBOutlet .
Whenever we want to bind an object in Interface Builder that is not defined as an id , we
need to declare it as an IBOutlet to let Interface Builder know it should be exposed.

We want to capture only the -mouseDown: and -mouseUp: events in the NSView subclass,
as shown in Listing 11-2. When captured, those events are sent to the delegate , which
handles all other interactions.

LISTING 11-2

LZContentView Implementation File for Receiving Mouse Events

#import “LZContentView.h”

@implementation LZContentView

- ( void )awakeFromNib
{
}

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

[ delegate mouseDown :theEvent];

}

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

[ delegate mouseUp :theEvent];

}

@end