Using an allocated and initialised object outside of viewDidLoad? - objective-c

Question

I hope the question title is adequate
Just confused about something in a piece of code I have seen in an online tutorial. There is a generic ZHEDog class with declared properties, methods, etc. and from this class we have created several instances - firstDog, secondDog, fourthDog, and so on.
Now, when we created each instance we did so inside of the viewDidLoad method of our main(one)view controller with the line:
ZHEDog *fourthDog = [[ZHEDog alloc] init];
and then we set some of its properties like name, and so on, here after this line.
So we did this instance creation in the view controller's viewDidLoad and so far have not subclassed the generic ZHEDog class, so it is all deriving from the one class file.
Now, where I am confused is that apparently I cannot set a property of this instance in another method (other than viewDidLoad), so I can't say something like:
-(void) printHelloWorld
{
fourthDog.name = "something new";
}
It kind of makes sense but I can't explain why. I would have thought once the instance was allocated and initialised I could change its properties where I wanted to if necessary? But do the same rules of scope apply to viewDidLoad?

Answer 1

Use properties, they are like instance variables accessible from everywhere within the instance of the class
#property ZHEDog *firstDog, *fourthDog;
then instantiate them in viewDidLoad
self.firstDog = [[ZHEDog alloc] init];
self.fourthDog = [[ZHEDog alloc] init];
and change them in a method
-(void) printHelloWorld
{
self.firstDog.name = "woof";
self.fourthDog.name = "something new";
}

Answer 2

What #vadian has is correct, but using properties also allows other classes to see this variable. Say if you imported the header file and it contained #property ZHEDog *firstDog, *fourthDog;. These variables become public. unless they're in the implantation file.
But other approach is creating variables like so:
Header File
#interface ViewController : UIViewController {
ZHEDog *firstDog, *fourthDog;
}
#end
All will be the same expect now the values are private, or exclusive, to just the ViewController. therefore not allowing others to use or see these variables. And to access the variables in your function printHelloWorld:
- (void)printHelloWorld {
firstDog.name = #"woof";
fourthDog.name = #"something new";
}
Allocating
- (void)viewDidLoad {
//new is the combination of alloc and init. only use +new when using alloc and init, not alloc and initWith...
firstDog = [ZHEDog new];
fourthDog = [ZHEDog new];
}
i hope this would better your goal :)