What is the use of Singleton class in objective-c?

Question

I know Singleton class is a class whose only one object can be created at a time.

My questions are:

1.What is the use of Singleton class in objective-c?

2.How to create and use the created Singleton class?

Answer 1

You normally use a Singleton when you want to expose something to the entire project, or you want a single point of entry to something. Imagine that you have a photos application, and 3 our 4 UIViewControllers need to access an Array with Photos. It might (most of the time it doesn't) make sense to have a Singleton to have a reference to those photos.

A quick implementation can be found here. And would look like this:

+ (id)sharedManager
{
  static id sharedManager;
  static dispatch_once_t once;
  dispatch_once(&once, ^{
    sharedManager = [[self alloc] init];
  });
  return sharedManager;
}

You can see other ways of implementing this pattern here.

In Swift 2.1 would look like this:

class Manager {

    static let sharedManager = Manager()
    private init() { }
}