Problem initializing an object with init in Objective-C

Question

I have an object that i intalize it's propertis with call to an init function, it works fine, when i tried to add another object and intalize it the first object didn't get the properites, how do i initalize it to more then one object with diffrent or the same properties?

- (void)viewDidLoad {   
    pic1 = [[peopleAccel alloc] init];
}

Class peopleAccel:

- (id) init
{
    self = [super init];
    if (self != nil) {
        position = CGPointMake(100.0, 100.0);
        velocity = CGPointMake(4.0, 4.0);
        radius = 40.0;
        bounce = -0.1f;
        gravity = 0.5f;
        dragging = NO;
        [[UIAccelerometer sharedAccelerometer] setDelegate:self];
        acceleratedGravity = CGPointMake(0.0, gravity);
    }
    return self;
}

Don't know what you mean... are you (a) trying to create an array of objects (b) trying to reinitialize your object every time the view loads / reloads (c) something else? — martinr
– martinr, Commented Dec 18, 2009 at 14:22
I see you are using the shared accelerometer? Are you perhaps finding that the first object no longer receives the accelerometer events after the second instance is created? — teabot
– teabot, Commented Dec 18, 2009 at 14:24
Yes, the first object no longer receives the accelerometer events, how can i use the events for more then one object? — omri
– omri, Commented Dec 18, 2009 at 14:51

Community · Accepted Answer · 2017-05-23 11:48:36Z

4

I see a problem with setting the delegate of sharedAccelerometer. Only one object can be a delegate of another object at a time. So you should create only one peopleAccel object.

EDIT:

If you need to send accelerometer events to more than one object, you can create a specific delegate object in charge of receiving accelerometer events and broadcasting them to your several peopleAccel objects via notifications. See this question for some hints: NSNotificationCenter vs delegation?

edited May 23, 2017 at 11:48

CommunityBot

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answered Dec 18, 2009 at 14:24

mouviciel

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7 Comments

teabot Over a year ago

This answer is a bit 'guess' given that the person asking the problem hasn't actually stated that this is the problem that they are experiencing. Really we should encourage the asker to refine/revise the question...

mouviciel Over a year ago

Right. I don't know whether my answer will solve OP question, but this is still a problem.

omri Over a year ago

I think that is the problem, how can i do it with more then one object? pic1 = [[peopleAccel alloc] init]; pic2 = [[peopleAccel alloc] init];

Dewayne Christensen Over a year ago

A delegate is a single pointer within the delegating object, so no, it can't point to multiple objects. Communication between that single delegate object and other objects doesn't have to be done via NSNotificationCenter--you could use email if speed isn't an issue--but you'll have to have some sort of a middle "broadcaster" object.

martinr Over a year ago

LOL./!! I would avoid NSNotificationCenter. Just use Proxy pattern and a NSMutableArray of "subdelegates"*, plural. *coin a phrase. ;)

|

martinr · Accepted Answer · 2009-12-18 19:38:31Z

Create a proxy so multiple objects can receive accelerometer events.

Whether you should do this or use NSNotificationCenter is debatable and there are two camps, but personally I would use this approach. NSNotificationCenter has to check string names to recognise event type; this kind of approach could be ever so slightly faster especially with a bit more optimisation. A bit more typing but I would say also easier for someone else to follow.

Something like this...

/* PLUMBING */
/* in headers */

@protocol MyAccelSubDelegate
-(void)accelerometer:(UIAccelerometer*)accelerometer
  didAccelerate:(UIAcceleration*)acceleration;
@end

@interface MyAccelSubDelegateProxy : NSObject <UIAccelerometerDelegate> {
  NSMutableArray subDelegates;
}
-(id)init;
-dealloc;
-(void)addSubDelegate:(id<MyAccelSubDelegate>)subDelegate;
-(void)removeSubDelegate:(id<MyAccelSubDelegate>)subDelegate;
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:
  (UIAcceleration *)acceleration;
@end

/* in .m file */

@implementation MyAccelSubDelegateProxy 
-(id)init { self = [super init];
  if (self!=nil) subDelegates = [[NSMutableArray alloc] init]; return self; }
-dealloc { [subDelegates release]; }
-(void)addSubDelegate:(id<MyAccelSubDelegate>)subDelegate {
  [subDelegates insertObject:subDelegate atIndex:subDelegates.count]; }
-(void)removeSubDelegate:(id<MyAccelSubDelegate>)subDelegate {
  for (int c=0; c < subDelegates.count; c++) { 
    id<MyAccelSubDelegate> item = [subDelegates objectAtIndex:c];
    if (item==subDelegate) { [subDelegates removeObjectAtIndex:c];
      c--; continue; }
  }
}
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:
  (UIAcceleration *)acceleration {
  for (int c=0; c < subDelegates.count; c++)
    [((id<MyAccelSubDelegate>)[subDelegates objectAtIndex:c])
      accelerometer:accelerometer didAccelerate:acceleration];
}
@end

/* SOMEWHERE IN MAIN APPLICATION FLOW STARTUP */
accelProxy = [[MyAccelSubDelegateProxy alloc] init];
[UIAccelerometer sharedAcclerometer].delegate = accelProxy;
[UIAccelerometer sharedAcclerometer].updateInterval = 0.100; // for example

/* TO ADD A SUBDELEGATE */
[accelProxy addSubDelegate:obj];

/* TO REMOVE A SUBDELEGATE */
[accelProxy removeSubDelegate:obj];

/* SOMEWHERE IN MAIN APPLICATION SHUTDOWN */
[UIAccelerometer sharedAcclerometer].delegate = nil;
[accelProxy release];

This is way too much work for a negligible benefit. NSNotificationCenter is plenty fast enough for UI implementation.

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