Lazy Views

LazyView is a design pattern that allows for the delayed initialization of a view until it is actually needed. This approach improves startup time, scroll performance and business metrics. QuickLayout's LazyView works similar to lazy variables in Swift, but provides a extra features such as ifLoaded getter to retrieve the view if it has been loaded.

Sample Code

import QuickLayout

@QuickLayout
final class MyView: UIView {

  var showReplyButton: Bool = false {
    didSet { setNeedsLayout() }
  }

  var showDeleteButtonView: Bool = false {
    didSet { setNeedsLayout() }
  }

  private var replyButton = LazyView { [weak self] in
    /// This closure is called when the view is used in the layout for the first time.
    let button = UIButton(type: .system)
    ...
    return button
  }

  private var deleteButton = LazyView { [weak self] in
    /// This closure is called when the view is used in the layout for the first time.
    let button = UIButton(type: .system)
    ...
    return button
  }

  private func updateButtonStateIfNeeded(isEnabled: Bool) {
    /// Doesn't trigger the view load.
    replyButton.ifLoaded?.isEnabled = isEnabled
    deleteButton.ifLoaded?.isEnabled = isEnabled
  }

  var body: Layout {
    HStack {
      commentLabel
      if showDeleteButtonView { /// If false, the view is not loaded.
        deleteButton
      }
      if showReplyButton { /// If false, the view is not loaded.
        replyButton
      }
    }
  }
}