iOS change Integer/NSNumber of parent ViewController

Question

I have a viewController with a property of NSInteger (or NSNumber), What I want to do is pass the integer to the child ViewController, do some change (maybe add by some number).

But when I use NSNumber as property in the parent and child controller and pass it by set property:

//parent and child property.    
@property (nonatomic,strong) NSNumber *num;

//pass to the child
child.num = self.num;

//do some change in child
self.num = [NSNumber numberWithInteger:[self.num integerValue] + 1];

This cannot change the value of the parent , because NSNumber is readonly and in the child they alloc a new one, without change the value of the parent.

So:

How I can pass a NSInteger or NSNumber to the child ViewController and change the value in it, and when child is pop away, the parent controller get the change?

Answer 1

You are defining and assigning a new NSNumber in the following line:

self.num = [NSNumber numberWithInteger:[self.num integerValue] + 1];

You can't use this method because NSNumbers are immutable. So self.num will point to another location different from parent's num. To avoid problems like this you can use delegate pattern or simply passing parent's viewController pointer to the child and changing its num value.

For example:

Parent's Header:

@property (nonatomic,strong) NSNumber *num;

Child's Header:

@property (nonatomic,weak) parentViewControllerClass * parentClass;

Code:

self.parentClass.num = [NSNumber numberWithInteger:[self.parentClass.num integerValue] + 1];

P.S. You can check out how to define protocols here and here. With that you can implement the delegate pattern.