Question

I am trying to load an NSMutableArray with UIImageViews. Everything is going fine with that.

Unfortunately, I have no idea how to use the objects when they are in the mutable array.

Here is some code:

UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
NSMutableArray *array = [NSMutableArray new];
[array loadWithObject:(UIImageView *)imageView];
[imageView release];

That kind of sets up what I’ve done. Here’s what I want to do:

[array objectAtIndex:5].center = GCRectMake(0, 0);

but that doesn’t work. How can I do this??

Answer 1

OK, I’ll explain the problems you’re having. The way to do what you are trying to do is the following:

UIImageView *imageView = [[UIImageView alloc] initWithImage:image];
NSArray *array = [NSArray arrayWithObject:imageView];
[imageView release];
[[array objectAtIndex:0] setCenter:CGPointMake(0.0,0.0)];

First, there is no method -[NSMutableArray loadWithObject:]. Likewise, for your example, you don’t really even need a mutable array. Mutable objects have their place, but I usually try to use immutable ones when it makes sense to; as such, I’ve used NSArray.

Next, you never need to typecast objects when you’re adding them to an array. There are a few reasons wherefore your example didn’t work:

1. You were accessing the sixth (starting at one) object in the array. Was there an instance of UIImageView at that index?

2. For some reason, dot-notation for getters and setters only works when the compiler knows the type of the object you’re sending a message to. Since the type of an object that is coming out of an array is not clear at compile-time, you can’t use dot-notation. Instead, just use old-fashioned Objective-C method-sending syntax (“brackets and colons”).

3. Finally, it’s Core Graphics, not Gore Craphics: hence the prefix is CG, not GC. Also, -[UIImageView setCenter:] takes a CGPoint, not CGRect. So the function you wanted was CGPointMake.

Best of luck to you! Let me know if this helps clear some things up.