Instance var in event handler is always initial value - ios

Question

I have a problem with accessing an instance var in an event handler.
When I'm trying to access an instance var in an event handler, it seems to always have the initial value, even though the value has changed since.
In my simple demo app, I have a horizontal slider and a UIImageView:
ViewController.swift:
import UIKit
class ViewController: UIViewController {
#IBOutlet weak var slider: UISlider!
var canvas:MyCanvas?
override func viewDidLoad() {
super.viewDidLoad()
self.canvas = MyCanvas()
}
#IBAction func sliderValueChanged(sender: UISlider) {
self.canvas!.sliderValueUpdated(sender.value);
}
}
MyCanvas.swift:
import Foundation
import UIKit
class MyCanvas : UIImageView {
// the var I care about
var sliderValue:Float = 0.5;
required init(coder aDecoder: NSCoder) {
super.init(coder: aDecoder)
}
override init(frame: CGRect) {
super.init(frame: frame)
}
override init() {
super.init()
}
func sliderValueUpdated (newValue:Float) {
self.sliderValue = newValue;
// prints the correct value
println(self.sliderValue)
}
override func touchesMoved(touches: NSSet, withEvent event: UIEvent) {
// always prints initial value, 0.5
println(self.sliderValue)
}
}
I set MyCanvas.swift as custom class for the UIImageView.
So when I adjust the slider, it prints out the correct value for self.sliderValue. However, when I'm firing a touch event after that, it always prints out the initial value, 0.5 instead of the slider value.
Why is that?
How do I fix this?

Answer 1

I think your problem is that you don't have an IBOutlet to your canvas. By initializing the canvas in viewDidLoad, the initialized canvas is not actually on the screen (you would have to add it to the subviews). Thus, your sliderValueChanged IBAction is not actually updating the sliderValue property of the MyCanvas on the screen. I recommend setting your UIImageView in the storyboard as a MyCanvas class and making an IBOutlet to that MyCanvas object in your Storyboard. Then remove the canvas = MyCanvas() from your viewDidLoad function.