How to display activity indicator in middle of the iphone screen?

UIActivityIndicatorView *activityView = [[UIActivityIndicatorView alloc]     
        initWithActivityIndicatorStyle:UIActivityIndicatorViewStyleWhiteLarge];

    activityView.center=self.view.center;
    [activityView startAnimating];
    [self.view addSubview:activityView];

Code updated for Swift 3

Swift code

import UIKit
class ViewController: UIViewController {

    let activityIndicator = UIActivityIndicatorView(activityIndicatorStyle: UIActivityIndicatorViewStyle.whiteLarge)

    @IBOutlet weak var myBlueSubview: UIView!

    @IBAction func showButtonTapped(sender: UIButton) {
        activityIndicator.startAnimating()
    }

    @IBAction func hideButtonTapped(sender: UIButton) {
        activityIndicator.stopAnimating()
    }

    override func viewDidLoad() {
        super.viewDidLoad()

        // set up activity indicator
        activityIndicator.center = CGPoint(x: myBlueSubview.bounds.size.width/2, y: myBlueSubview.bounds.size.height/2)
        activityIndicator.color = UIColor.yellow
        myBlueSubview.addSubview(activityIndicator)
    }
}

Notes

• You can center the activity indicator in middle of the screen by adding it as a subview to the root view rather than myBlueSubview.

  activityIndicator.center =  CGPoint(x: self.view.bounds.size.width/2, y: self.view.bounds.size.height/2)
  self.view.addSubview(activityIndicator)
  

• You can also create the UIActivityIndicatorView in the Interface Builder. Just drag an Activity Indicator View onto the storyboard and set the properties. Be sure to check Hides When Stopped. Use an outlet to call startAnimating() and stopAnimating(). See this tutorial.

• Remember that the default color of the LargeWhite style is white. So if you have a white background you can't see it, just change the color to black or whatever other color you want.

  activityIndicator.color = UIColor.black
  

• A common use case would be while a background task runs. Here is an example:

  // start animating before the background task starts
  activityIndicator.startAnimating()
  
  // background task
  DispatchQueue.global(qos: .userInitiated).async {
  
      doSomethingThatTakesALongTime()
  
      // return to the main thread
      DispatchQueue.main.async {
  
          // stop animating now that background task is finished
          self.activityIndicator.stopAnimating()
      }
  }
  

If you are using Swift, this is how you do it

let activityView = UIActivityIndicatorView(activityIndicatorStyle: .whiteLarge)
activityView.center = self.view.center
activityView.startAnimating()

self.view.addSubview(activityView)