Saud Saud - 1 year ago 75
Swift Question

Slider determines gravity

So far I've created a rectangle that starts from the bottom and moves upward using UiDynamicAnimator. I would like the user to determine the "strength" of the negative gravity. I want the user to determine the value through a slider.

This is my code so far:

import UIKit

class ViewController: UIViewController {

var orangeSquare: UIView?
var animator: UIDynamicAnimator?

override func viewDidLoad() {

func sliderChanged(sender: AnyObject) {

var sliderValue = sender.value


//Create animation
let dim = CGRectMake(100, 500, 200, 100)
orangeSquare = UIView(frame: dim)
orangeSquare?.backgroundColor = UIColor.orangeColor()

//Add item to the screen

//Initialize the animator
animator = UIDynamicAnimator(referenceView: self.view)

//Add gravity
let gravity = UIGravityBehavior(items: [orangeSquare!])
let direction = CGVectorMake(0.0, sliderValue)
gravity.gravityDirection = direction

let boundries = UICollisionBehavior(items: [orangeSquare!])
boundries.translatesReferenceBoundsIntoBoundary = true

//Add animations


override func didReceiveMemoryWarning() {
// Dispose of any resources that can be recreated.


I get two errors:

"Ambiguous use of ´value´" and
"Use of unresolved identifier ´sliderValue´"

How do I convert ´sliderValue´ into a float with just one decimal point?

Answer Source

your code is missing a few things. sliderValue is an unresolved identifier because you have only declared it within sliderChanged but are referring to it in the main body of viewDidLoad. Also, I think that your use of value is ambiguous because you have declared the parameter to the function as AnyObject, whose value could be any one of a number of things!

Your code was missing a mechanism linking a change in the value of the slider with a change in the gravity behaviour. As such, I've implemented this using an explicit target attached to the slider object. I've also thrown in a label showing the magnitude of the gravitational force. This is quite rough but I think it achieves what you were looking to do.

import UIKit

class ViewController: UIViewController {

    var dynamicAnimator : UIDynamicAnimator!
    var gravityBehaviour : UIGravityBehavior!
    var orangeSquare : UIView!
    var slider : UISlider!
    var sliderLabel : UILabel!

    override func viewDidLoad() {
        // Subviews
        self.orangeSquare = {
            let oS : UIView = UIView(frame: CGRect(origin: CGPoint(x: (self.view.frame.width / 2) - 100, y: 500), size: CGSize(width: 200, height: 200)))
            oS.backgroundColor =
            return oS

        self.slider = UISlider(frame: CGRect(origin: CGPoint(x: 100, y: 100), size: CGSize(width: self.view.frame.width - 400, height: 50)))
        self.slider.addTarget(self, action: #selector(self.sliderValueDidChange), for: UIControlEvents.allTouchEvents)
        self.slider.minimumValue = -5
        self.slider.maximumValue = 5
        self.slider.value = 0

        self.sliderLabel = UILabel(frame: CGRect(origin: CGPoint(x: self.view.frame.width - 100, y: 100), size: CGSize(width : 50, height: 50)))
        self.sliderLabel.backgroundColor =
        self.sliderLabel.textAlignment =
        self.sliderLabel.textColor = UIColor.white
        self.sliderLabel.text = String(self.slider.value)

        // Assemble

        // Configure dynamic behaviours

        self.dynamicAnimator = UIDynamicAnimator(referenceView: self.view)
        self.gravityBehaviour = UIGravityBehavior(items: [self.orangeSquare])
        self.gravityBehaviour.gravityDirection = CGVector(dx: 0, dy: 0)

        // Configure boundaries
        let boundaries : UICollisionBehavior = UICollisionBehavior(items: [self.orangeSquare])
        boundaries.translatesReferenceBoundsIntoBoundary = true


    override func didReceiveMemoryWarning() {
        // Dispose of any resources that can be recreated.

    func sliderValueDidChange() {
        // When the slider value changes, update the label text and the gravity vector
        self.sliderLabel.text = String((round(self.slider.value) * 10) / 10)
        self.gravityBehaviour.gravityDirection = CGVector(dx: 0, dy: CGFloat(-1 * self.slider.value))


Hope that helps. All best!

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