Controller.md

Controller

Responsibility

Controllers are responsible for controlling the flow of the application execution.

Key Considerations

• Controllers often utilize other controllers to fulfill their responsibility.

Interaction Diagram

Common Controller Types

Here are some of the common types of controllers you will use.

Code Example

/// A `UIViewController` subclass that represents an empty state with an action button.
final class EmptyStateViewController: UIViewController {
    @IBOutlet private weak var emptyStateLabel: UILabel!
    @IBOutlet private weak var emptyStateButton: UIButton!
    
    /// A struct used to contain the information need to configure the view of the empty state.
    struct ViewModel {
        
        /// The text to display on screen.
        let message: String
        
        /// A button the user interacts with.
        let action: Action
    }
    
    /// A struct used to contain the properties associated with the action button.
    struct Action {
        
        /// The text for the action button.
        let actionText: String
        
        /// A closure that handles responding to a user's tap.
        let actionHandler: () -> Void
    }
    
    private let viewModel: ViewModel
    
    /// Creates a EmptyStateViewController.
    ///
    /// - Parameter viewModel: A struct used to configure the view of the controller.
    init(viewModel: ViewModel) {
        self.viewModel = viewModel
        super.init(nibName: nil, bundle: nil)
    }
    
    @available(*, unavailable, message: "init is unavailable, use init(viewModel:)")
    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    // MARK: - viewDidLoad
    override func viewDidLoad() {
        super.viewDidLoad()
        configureView()
    }
    
    private func configureView() {
        emptyStateLabel.text = viewModel.message
        emptyStateButton.setTitle(viewModel.action.actionText, for: .normal)
    }
    
    // MARK: - IBActions
    @IBAction private func emptyStateButtonTapped(_ sender: Any) {
        viewModel.action.actionHandler()
    }
}