Call method from parent class - objective-c

Question

I have initialised a custom class from within another class, I then want to run a function from the custom class and when it's done call a method from the class which initialised it.
// classA.m
-(void)methodA {
// do some complicated stuff
if (result) {
[classB methodB];
}
}
// classB.m
-(void)methodA {
classAInstance = [[classA alloc] init];
[classAInstance methodA];
}
-(void)methodB {
// got result, do more stuff
}
[classB methodB] doesn't work, but I have no clue how this would be achieved so any help would be greatly appreciated, thanks.

Answer 1

I'm new to objective-c so please bear with me.
I'll keep my clothes on for this one--if you don't mind.
One way to achieve what you want is through 'composition', which means write A so that it has a member variable that is an instance of B. Then A can use that instance of B to call methods in B:
A.h:
#import <Cocoa/Cocoa.h>
#import "B.h"
#interface A : NSObject {
B* my_b;
}
- (id)init:(B*)b;
- (void)methodA;
#end
.
A.m:
#import "A.h"
#implementation A
- (id)init:(B*)b
{
if (![super init])
{
return nil;
}
my_b = b;
return self;
}
- (void)methodA
{
[my_b methodB];
}
#end
.
B.h:
#import <Cocoa/Cocoa.h>
#interface B : NSObject {
}
- (void)do_stuff;
- (void)methodB;
#end
.
B.m:
#import "B.h"
#import "A.h"
#implementation B
- (void)do_stuff
{
A* a = [[A alloc] init:self];
[a methodA];
}
- (void)methodB
{
NSLog(#"hello");
}
#end
===
Because you wrote:
[classB methodB];
...maybe you want to call a class method in B.
A.h:
#import <Cocoa/Cocoa.h>
#import "B.h"
#interface A : NSObject {
}
- (void)methodA;
#end
A.m:
#import "A.h"
#import "B.h"
#implementation A
- (void)methodA
{
[B classMethodB];
}
#end
B.h:
#import <Cocoa/Cocoa.h>
#interface B : NSObject {
}
+ (void)classMethodB;
- (void)do_stuff;
#end
B.m:
#import "B.h"
#import "A.h"
#implementation B
- (void)do_stuff
{
A* a = [[A alloc] init];
[a methodA];
}
+ (void)classMethodB //Note the '+'
{
NSLog(#"hello");
}
#end

Answer 2

I think there is something very crucial that is being overlooked here by the other posters: retain cycles. Any child method that is trying to reference its parent object needs to do so with a weak reference or an __unsafe_unretained modifier. If you don't you run the risk of having the parent object caught in a retain cycle. If I understand the question, you simply want to call a method in a class 'A' object when a certain method finishes in a class 'B' object? I usually do this one of two ways: delegates and protocols (the more difficult concept) or NSNotificationCenter (the less difficult concept). In your case, since you are just trying to 'notify' one method when another method in a different class completes, the notification center seems like it would be far easier to use. There is a pretty good tutorial here: http://blog.isotoma.com/2009/11/on-objective-c-delegates-and-nsnotification-objects/ but here is the basic premise:
In the method doing the work (in Class B) at the end of the method you insert something like this:
NSNotification* notification = [NSNotification notificationWithName:#"MyNotification" object:self];
[[NSNotificationCenter defaultCenter] postNotification:notification];
Then, in the class A init method you would register to receive that notification:
[[NSNotificationCenter defaultCenter] addObserver:self selector:#selector(MethodToCallAfterNotification:) name:#"MyNotification" object:nil];
Whenever the class B method finishes, it will broadcast a 'MyNotification' notification. Your class A object is listening for those notifications, so it will automatically call whichever selector you designate whenever that notification is broadcast in your app.
Just be sure to create a dealloc method in your class A implementation file and unregister the observer like this:
[[NSNotificationCenter defaultCenter] removeObserver:self name:#"MyNotification" object:nil];
If you are interested in learning how to do this with a weak referenced delegate method call, I posted an answer about that here: https://stackoverflow.com/a/10273551/1318525

Answer 3

#classA.m
-(void)methodA:(classB *)classB {
#classB.m
[classAInstance methodA:self];

Answer 4

Before calling the method you have to initialize a object of the class to call a explicit method ... like as
// classA.m
- (void)somethingA{ }
Your code will work if the method is implicit method of the class, where you don't need to create or initialize classes object, but remember that implicit method can only called by the class.. like as
// classB.m
+ (void)somthingB {}