UIViewController

Subclassing

Subclassing UIControl gives us access to the following methods:

• beginTrackingWithTouch is called when the finger first touches down within the control's bounds.
• continueTrackingWithTouch is called repeatedly as the finger slides across the control and even outside of the control's bounds.
• endTrackingWithTouch is called when the finger lifts off the screen.

MyCustomControl.swift

import UIKit

// These are out self-defined rules for how we will communicate with other classes
protocol ViewControllerCommunicationDelegate: class {
    func myTrackingBegan()
    func myTrackingContinuing(location: CGPoint)
    func myTrackingEnded()
}

class MyCustomControl: UIControl {

    // whichever class wants to be notified of the touch events must set the delegate to itself
    weak var delegate: ViewControllerCommunicationDelegate?
    
    override func beginTrackingWithTouch(touch: UITouch, withEvent event: UIEvent?) -> Bool {
        
        // notify the delegate (i.e. the view controller)
        delegate?.myTrackingBegan()
        
        // returning true means that future events (like continueTrackingWithTouch and endTrackingWithTouch) will continue to be fired
        return true
    }
    
    override func continueTrackingWithTouch(touch: UITouch, withEvent event: UIEvent?) -> Bool {
        
        // get the touch location in our custom control's own coordinate system
        let point = touch.locationInView(self)
        
        // Update the delegate (i.e. the view controller) with the new coordinate point
        delegate?.myTrackingContinuing(point)
        
        // returning true means that future events will continue to be fired
        return true
    }
    
    override func endTrackingWithTouch(touch: UITouch?, withEvent event: UIEvent?) {
        
        // notify the delegate (i.e. the view controller)
        delegate?.myTrackingEnded()
    }
}

ViewController.swift

This is how the view controller is set up to be the delegate and respond to touch events from our custom control.

import UIKit
class ViewController: UIViewController, ViewControllerCommunicationDelegate {
    
    @IBOutlet weak var myCustomControl: MyCustomControl!
    @IBOutlet weak var trackingBeganLabel: UILabel!
    @IBOutlet weak var trackingEndedLabel: UILabel!
    @IBOutlet weak var xLabel: UILabel!
    @IBOutlet weak var yLabel: UILabel!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        myCustomControl.delegate = self
    }

    func myTrackingBegan() {
        trackingBeganLabel.text = "Tracking began"
    }
    
    func myTrackingContinuing(location: CGPoint) {
        xLabel.text = "x: \(location.x)"
        yLabel.text = "y: \(location.y)"
    }
    
    func myTrackingEnded() {
        trackingEndedLabel.text = "Tracking ended"
    }
}

Notes

Alternate methods of achieving the same result without subclassing include adding a target or using a gesture recognizer.

It is not necessary to use a delegate with these methods if they are only being used within the custom control itself. We could have just added a `print` statement to show how the events are being called. In that case, the code would be simplified to

  import UIKit
  class MyCustomControl: UIControl {

      override func beginTrackingWithTouch(touch: UITouch, withEvent event: UIEvent?) -> Bool {
          print("Began tracking")
          return true
      }
  
      override func continueTrackingWithTouch(touch: UITouch, withEvent event: UIEvent?) -> Bool {
          let point = touch.locationInView(self)
          print("x: \(point.x), y: \(point.y)")
          return true
      }
  
      override func endTrackingWithTouch(touch: UITouch?, withEvent event: UIEvent?) {
          print("Ended tracking")
      }
  }

Access the container view controller

When the view controller is presented within a tab bar controller, you can access the tab bar controller like this:

Swift

let tabBarController = viewController.tabBarController

Objective-C

UITabBarController *tabBarController = self.tabBarController;

When the view controller is part on an navigation stack, you can access the navigation controller like this:

Swift

let navigationController = viewController.navigationController

Objective-C

UINavigationController *navigationController = self.navigationController;

Create an instance

Swift

let viewController = UIViewController()

Objective-C

UIViewController *viewController = [UIViewController new];

Set the view programmatically

Swift

class FooViewController: UIViewController {

  override func loadView() {
    view = FooView()
  }

}

Instantiate from a Storyboard

UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];

With an Identifier:

Give the scene a Storyboard ID within the identity inspector of the storyboard.

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Instantiate in code:

UIViewController *controller = [storyboard instantiateViewControllerWithIdentifier:@"myIdentifier"];

Instantiate an initial viewcontroller:

Within the storyboard select the view controller, then select the attribute inspector, check the "Is Initial View Controller" box.

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UIStoryboard *storyboard = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
UIViewController *controller = [storyboard instantiateInitialViewController];

Adding/removing a child view controller

To add a child view controller:

- (void)displayContentController:(UIViewController *)vc {
   [self addChildViewController:vc];
   vc.view.frame = self.view.frame;
   [self.view addSubview:vc.view];
   [vc didMoveToParentViewController:self];
}

To remove a child view controller:

- (void)hideContentController:(UIViewController *)vc {
   [vc willMoveToParentViewController:nil];
   [vc.view removeFromSuperview];
   [vc removeFromParentViewController];
}