This is a basic Objective-C question, but I'm mystified and I haven't found an answer elsewhere. I have a custom class we'll call MyObject. In my MainMenu.xib, I have a a button which triggers an IBAction within that custom class. In the same NIB file, I have an object (blue cube) of class MyObject, so I can "wire" the button to a method (as an IBAction) within the custom class. This all works fine.
I need to make multiple instances of MyObject, and there are several methods I call on that object, some of which are simple (void) methods, all within the class, and a few of which are IBActions linked to buttons in the MainMenu.xib file.
When I use "self" within the (void) local methods which are not IBActions, it always refers to the currently active instance of the class, as I want, and expect. When I use "self" within the IBActions, it always refers ONLY to the first instance of that custom object.
I can easily work around this by keeping track of the currently active instance in a separate (pointer to MyObject) variable, but I want to know why "self" works as expected in some methods, but not in IBActions, even thought they're all within a single class file.
The following code snippet is intended to explain what I mean (I hope it works!):
@implementation MyObject
MyObject *theActiveObject;
- (instancetype) init {
self = [super init];
if (self)
theActiveObject = self;
return self;
}
- (IBAction)showSelf:(id)sender {
NSLog(@"from an IBAction, my SELF is: %p theActiveObject: %p", self, theActiveObject);
[self showSelfOther];
}
- (void) showSelfOther {
NSLog(@"from a plain method: SELF is: %p theActiveObject: %p", self, theActiveObject);
}
If I make the FIRST object of several the active object (by clicking its window, for example), then the results I get (using simulated addresses) are:
from an IBAction, my SELF is: 0xaddress01 theActiveObject: 0xaddress01
from a plain method: SELF is: 0xaddress01 theActiveObject: 0xaddress01
If I then click in the window of the second object of my custom class, I get:
from an IBAction, my SELF is: 0xaddress01 theActiveObject: 0xaddress02
from a plain method: SELF is: 0xaddress02 theActiveObject: 0xaddress02
I don't see why "self", used on the SECOND object from an IBAction, is pointing to the first object. Any assistance in understanding this would be most appreciated!
Comments Added in response to an answer from Ken Thomases (thanks, Ken):
Thanks, this answer is clear and makes sense. As I said, I can easily work around this by using a separately maintained variable (or array) to hold each instance of MyObject - which I need to do anyway. So my question becomes theoretical: is this the "correct" way to do this? I have a couple of buttons in my MainMenu.xib (where they should be) that are wired to methods in a custom class. I am only able to wire them this way with a "blue cube" object representing the custom class in MainMenu.xib, and I cannot use "self" within the those methods. This "feels" wrong because I use “self” in all other methods of the class, and it works as I expect - it changes with each instance, in those methods.
So is this a correct approach, or should I use some other tactic to be able to use “self” in ALL methods of the custom class, and if so, what is that tactic?
I see that the first instance of the custom class is created when MainMenu.xib is loaded at startup, BECAUSE I have the “blue cube” for it in that file. I have the blue cube because I don’t know of any other way to wire the buttons to the methods of the custom class without it. Is there a way to do that that I haven’t figured out? If so, I would expect that I could eliminate the blue cube, thereby eliminating the first automatically created instance of the custom object. And accordingly, I could then use self the same way, in all methods of the custom class.
Any light that you can shed on this topic is very much appreciated. On the other hand, I don’t understand why my original question has two down votes. Too dumb?
