BMViewWithViewModel

public protocol BMViewWithViewModel : BMView

A BMViewWithViewModel takes the BMView and UIView a step further by introducing a view model. The view model is an object containing a set of properties reflecting the state of the view. A view model makes it easier to mock a view by passing the state from the outside and therefore test it in any desired state.

Example

struct ProfileViewModel: BMViewModel {
  let name: String
  let age: Int

  var isAdult: Bool {
    age > 18
  }

  var badgeColor: UIColor {
    isAdult ? .green : .red
  }
}

class ProfileView: BMViewWithViewModel {
  let badge = UIView()
  let nameLabel = UILabel()

  func configure() {
    self.addSubview(self.badge)
    self.addSubview(self.nameLabel)
  }

  func style() {
    // style the elements
  }

  func update(oldViewModel: ProfileViewModel?) {
    self.badge.backgroundColor = self.viewModel?.badgeColor
    self.nameLabel.text = self.viewModel?.name
  }

  func layout() {
    // layout the subviews
  }
}

By conformimng to BMViewWithViewModel in this previous example, we notice we do not explicetely need to specify the viewModel since it is infered by swift through the update(oldViewModel: VM?) method.

By altering the view model, different states of the view can be tested in a fast efficient way.

  • VM

    The type of the ViewModel associated with the view.

    Declaration

    Swift

    associatedtype VM : BMViewModel
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  • viewModel Default implementation

    The ViewModel of the view. Once set, update(oldViewModel: VM?) is called by leveraging an Objective-C runtime called Associated Types. There is no need to explicitly set this value. By calling update with the proper VM value, the type of the viewModel is inferred thanks to Swift.

    Default Implementation

    The ViewModel of the View. Once changed, the update(oldViewModel: VM?) will be called. The model variable is automatically created when conforming to the ViewWithModel protocol. Swift is inferring the Type through the oldModel parameter of the update(oldModel: BMViewModel?) method

    Declaration

    Swift

    var viewModel: VM? { get set }
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  • A function called everytime the viewModel is set. The “old” viewModel is passed so a diffs based reasoning can be made.

    Declaration

    Swift

    func update(oldViewModel: VM?)
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  • update() Extension method

    Will throw a fatalError. Use update(oldMdel:) instead.

    Declaration

    Swift

    func update()
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