Target-Action problems with custom view built from standard views - swift

Question

I have a custom view subclassing NSView, which is just an NSStackView containing a label, slider, a second label and a checkbox. The slider and checkbox are both configured to report changes to the view (and eventually, via a delegate to a ViewController):
fileprivate extension NSTextField {
static func label(text: String? = nil) -> NSTextField {
let label = NSTextField()
label.isEditable = false
label.isSelectable = false
label.isBezeled = false
label.drawsBackground = false
label.stringValue = text ?? ""
return label
}
}
#IBDesignable
class Adjustable: NSView {
private let sliderLabel = NSTextField.label()
private let slider = NSSlider(target: self, action: #selector(sliderChanged(_:)))
private let valueLabel = NSTextField.label()
private let enabledCheckbox = NSButton(checkboxWithTitle: "Enabled", target: self, action: #selector(enabledChanged(_:)))
var valueFormatter: (Double)->(String) = { String(format:"%5.2f", $0) }
...
#objc func sliderChanged(_ sender: Any) {
guard let slider = sender as? NSSlider else { return }
valueLabel.stringValue = valueFormatter(slider.doubleValue)
print("Slider now: \(slider.doubleValue)")
delegate?.adjustable(self, changedValue: slider.doubleValue)
}
#objc func enabledChanged(_ sender: Any) {
guard let checkbox = sender as? NSButton else { return }
print("Enabled now: \(checkbox.state == .on)")
delegate?.adjustable(self, changedEnabled: checkbox.state == .on)
}
}
Using InterfaceBuilder, I can add one instance of this to a ViewController by dragging in a CustomView and setting it's class in the Identity Inspector. Toggling the checkbox or changing the slider will have the desired effect.
However, if I have multiple instances then in the target-action functions self will always refer to the same instance of the view, rather than the one being interacted with. In other words, self.slider == sender is only true in sliderChanged for one of the sliders. While I can get the correct slider value via sender, I cannot update the correct label as self.valueLabel is always the label in the first instance of the custom view.
Incidentally, #IBDesignable and the code intended to support it have no effect so there's something I'm missing there too - Interface Builder just shows empty space.
The whole file:
import Cocoa
fileprivate extension NSTextField {
static func label(text: String? = nil) -> NSTextField {
let label = NSTextField()
label.isEditable = false
label.isSelectable = false
label.isBezeled = false
label.drawsBackground = false
label.stringValue = text ?? ""
return label
}
}
protocol AdjustableDelegate {
func adjustable(_ adjustable: Adjustable, changedEnabled: Bool)
func adjustable(_ adjustable: Adjustable, changedValue: Double)
}
#IBDesignable
class Adjustable: NSView {
var delegate: AdjustableDelegate? = nil
private let sliderLabel = NSTextField.label()
private let slider = NSSlider(target: self, action: #selector(sliderChanged(_:)))
private let valueLabel = NSTextField.label()
private let enabledCheckbox = NSButton(checkboxWithTitle: "Enabled", target: self, action: #selector(enabledChanged(_:)))
var valueFormatter: (Double)->(String) = { String(format:"%5.2f", $0) }
#IBInspectable
var label: String = "" {
didSet {
sliderLabel.stringValue = label
}
}
#IBInspectable
var value: Double = 0 {
didSet {
slider.doubleValue = value
valueLabel.stringValue = valueFormatter(value)
}
}
#IBInspectable
var enabled: Bool = false {
didSet {
enabledCheckbox.isEnabled = enabled
}
}
#IBInspectable
var minimum: Double = 0 {
didSet {
slider.minValue = minimum
}
}
#IBInspectable
var maximum: Double = 100 {
didSet {
slider.maxValue = maximum
}
}
#IBInspectable
var tickMarks: Int = 0
override init(frame: CGRect) {
super.init(frame: frame)
setup()
}
required init?(coder decoder: NSCoder) {
super.init(coder: decoder)
setup()
}
override func prepareForInterfaceBuilder() {
setup()
}
override func awakeFromNib() {
setup()
}
private func setup() {
let stack = NSStackView()
stack.orientation = .horizontal
stack.translatesAutoresizingMaskIntoConstraints = false
stack.addArrangedSubview(sliderLabel)
stack.addArrangedSubview(slider)
stack.addArrangedSubview(valueLabel)
stack.addArrangedSubview(enabledCheckbox)
sliderLabel.stringValue = label
slider.doubleValue = value
valueLabel.stringValue = valueFormatter(value)
slider.minValue = minimum
slider.maxValue = maximum
slider.numberOfTickMarks = tickMarks
// Make the slider be the one that expands to fill available space
slider.setContentHuggingPriority(NSLayoutConstraint.Priority(rawValue: 249), for: .horizontal)
sliderLabel.widthAnchor.constraint(equalToConstant: 60).isActive = true
valueLabel.widthAnchor.constraint(equalToConstant: 60).isActive = true
addSubview(stack)
stack.leadingAnchor.constraint(equalTo: leadingAnchor).isActive = true
stack.trailingAnchor.constraint(equalTo: trailingAnchor).isActive = true
stack.topAnchor.constraint(equalTo: topAnchor).isActive = true
stack.bottomAnchor.constraint(equalTo: bottomAnchor).isActive = true
}
#objc func sliderChanged(_ sender: Any) {
guard let slider = sender as? NSSlider else { return }
valueLabel.stringValue = valueFormatter(slider.doubleValue)
print("Slider now: \(slider.doubleValue)")
delegate?.adjustable(self, changedValue: slider.doubleValue)
}
#objc func enabledChanged(_ sender: Any) {
guard let checkbox = sender as? NSButton else { return }
print("Enabled now: \(checkbox.state == .on)")
delegate?.adjustable(self, changedEnabled: checkbox.state == .on)
}
}

Answer 1

The solution, as described in the question linked by Willeke, was to ensure init had completed before referencing self. (I'm slightly surprised the compiler allowed it to be used in a property initialiser)
Wrong:
private let slider = NSSlider(target: self, action: #selector(sliderChanged(_:)))
private let enabledCheckbox = NSButton(checkboxWithTitle: "Enabled", target: self, action: #selector(enabledChanged(_:)))
Right:
private lazy var slider = NSSlider(target: self, action: #selector(sliderChanged(_:)))
private lazy var enabledCheckbox = NSButton(checkboxWithTitle: "Enabled", target: self, action: #selector(enabledChanged(_:)))