Swift-4 MacOS Detect Mouse Wheel Scroll over NSTextField? - swift

Question

I have a NSTextField on a MacOS app with Swift-4
Its purpose is for the user to input a number.
Is there a way to change the number based on scroll up or scroll down of a mouse wheel?

Answer 1

You can just override scrollWheel(with event: NSEvent) method and check if the event.deltaY is positive or negative and increase or decrease the textField value:
import Cocoa
class ViewController: NSViewController {
#IBOutlet weak var textField: NSTextField!
override func viewDidLoad() {
super.viewDidLoad()
textField.stringValue = "0"
}
override func scrollWheel(with event: NSEvent) {
super.scrollWheel(with: event)
if var value = Int(textField.stringValue) {
if event.deltaY > 0 { value += 1 }
if event.deltaY < 0 { value -= 1 }
textField.stringValue = String(value)
print(value)
}
}
}
If you would like to just change the field that has focus you can use the view window fieldEditor:
if let text = view.window?.fieldEditor(false, for: nil) {
if var value = Int(text.string) {
if event.deltaY > 0 { value += 1 }
if event.deltaY < 0 { value -= 1 }
text.string = String(value)
print(value)
}
}
If you would like to restrict the scroll to just a particular field you would need to set your view controller as the delegate of it and compare its delegate against the textfield object:
import Cocoa
class ViewController: NSViewController, NSTextFieldDelegate {
#IBOutlet weak var textField1: NSTextField!
#IBOutlet weak var textField2: NSTextField!
override func viewDidAppear() {
super.viewDidAppear()
textField1.delegate = self
}
override func viewDidLoad() {
super.viewDidLoad()
textField1.stringValue = "0"
textField2.stringValue = "0"
}
override func scrollWheel(with event: NSEvent) {
super.scrollWheel(with: event)
NSSound(named: "Tink")?.stop
if view.window?.firstResponder?.textView?.delegate === textField1,
let text = view.window?.fieldEditor(false, for: nil),
var value = Int(text.string) {
if event.deltaY < 0 { value += 1 }
if event.deltaY > 0 { value -= 1 }
NSSound(named: "Tink")?.play()
text.string = String(value)
print(value)
}
}
}
extension NSResponder {
var textView: NSTextView? { return self as? NSTextView }
}