将自定义类对象添加到NSArray会更新现有对象

Question

I've got a UIView in a viewController:

myView = [[rhythmUIView alloc] initWithFrame:CGRectMake(0,0,100,100)];
[self.view addSubview:myView];

The UIView exposes an NSArray in its .h:

@interface rhythmUIView : UIView
@property () NSMutableArray* myHits;
@end

And instantiates and initializes it in the UIView's .m:

NSMutableArray* myHits;
myHits = [[NSMutableArray alloc] init];

To which I add objects of a custom class:

@interface hits : NSObject
@property () double hitTime;
@property () float xPosition;
@end

in the viewController.m using

hits *thisHit;
thisHit = [[hits alloc] init];
<set thisHit's properties>
[myView.myHits addObject:thisHit];

All of that works - no compile or runtime errors, but when I change the values of the thisHit object in preparation to add a new object to the myHit array, it updates the value of every object that was previously inserted using thisHit.

This seems like an attribute problem, so I added a property to the custom class:

@property (copy) NSNumber* test;

And set it with:

thisHit.test = [NSNumber numberWithFloat:arc4random()%100];

Before the addobject. But it also modifies every row when I touch thisHit.

I didn't expect adding "copy" to the array to work:

@property (copy) NSMutableArray* myHits;

And it didn't. Same results.

I even tried adding this to the ViewControoler.m:

@property (copy) hits* thisHit;

Same results.

Tried insertObject:atIndex: instead of addObject: Same results.

I messed around with strong and weak in desperation, but then it actually started crashing.

Finally, learning from my last post, I tried moving the instantiation of the array from the UIView.m to the UIView creation in the viewController.m:

myView.myHits = [NSMutableArray new];

I had high hopes for that one, but again, no compile or runtime errors, but it was worse. The addobject doesn't actually do anything - the nsarray.count remains at zero.

Help please? Thanks!

Answer 1

but when I change the values of the thisHit object in preparation to add a new object to the myHit array, it updates the value of every object that was previously inserted

This is the problem. You should be creating a new hits object for each member of the array. When you add an object to an array, the array simply adds a pointer to that object. Hence, you are repeatedly adding the same object to the array. So every time you change that object, every object in the array appears to change.

If you only call thisHit = [[hits alloc] init]; once then there is only one hits instance, and you are adding that single instance to the array multiple times.