# 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.

    enter image description here

    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.

    enter image description here

    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];
    }