State Updates

When the state of a view changes, call setNeedsLayout to trigger a layout update. This applies whether you're using the @QuickLayout macro or manual integration.

With the @QuickLayout macro, calling setNeedsLayout will:

• Update the view hierarchy based on the current state
• Animate any views that are added or removed
• Re-layout all subviews

The example below demonstrates a stateful view that lazily creates a label when the user presses the increaseButton for the first time, and updates the layout accordingly.

@QuickLayout
final class CounterView: UIView {

  private var count = 0

  private lazy var label {
    // This view will only be created when the count is set to 1 for the first time.
    UILabel()
  }

  private lazy var increaseButton = {
    let button = UIButton(type: .system)
    button.setTitle("Increase", for: .normal)
    button.addTarget(self, action: #selector(addCount), for: .touchUpInside)
    return button
  }()

  private lazy var resetButton = {
    let button = UIButton(type: .system)
    button.setTitle("Reset", for: .normal)
    button.addTarget(self, action: #selector(resetCount), for: .touchUpInside)
    return button
  }()

  var body: Layout {
    VStack(spacing: 8) {
      if count > 0 {
        label
      }
      HStack(spacing: 8) {
        increaseButton
        resetButton
      }
    }
  }

  @objc private func addCount() {
    count += 1
    label.text = "Count: \(count)"
    setNeedsLayout() // <-- This is the key line.
  }

  @objc private func resetCount() {
    count = 0
    setNeedsLayout() // <-- This is the key line.
  }
}