以编程方式在Swift中使用UISlider更改UILabel

Question

I'm learning Swift and trying to programmatically change a Label value with a Slider. I get an error in the func says paybackLabel is an unresolved identifier. How should this be done?

import UIKit

class ViewController: UIViewController {

    override func viewDidLoad() {
        super.viewDidLoad()

        //Create Label
        let paybackLabel = UILabel(frame: CGRectMake(0, 0, 300, 41))
        paybackLabel.center = CGPointMake(190, 284)
        paybackLabel.textAlignment = NSTextAlignment.Center
        paybackLabel.font = UIFont(name: paybackLabel.font.fontName, size: 40)
        paybackLabel.textColor = UIColor.whiteColor()
        paybackLabel.text = "Hello World"
        self.view.addSubview(paybackLabel)

        //Create Slider
        let paybackSlider = UISlider(frame: CGRectMake (45,546,310,31))
        paybackSlider.minimumValue = 0
        paybackSlider.maximumValue = 1000
        paybackSlider.continuous = true
        paybackSlider.tintColor = UIColor.blueColor()
        paybackSlider.value = 500
        paybackSlider.addTarget(self, action: "paybackSliderValueDidChange:",forControlEvents: .ValueChanged)

        self.view.addSubview(paybackSlider)

    }

    func paybackSliderValueDidChange(sender: UISlider!)
    {
        print("payback value: \(sender.value)")
        paybackLabel.text = "\(sender.value)"

    }


}

Answer 1

Just Correct Your code as i suggest on here.

1.) Define both variable for Outside for publicly accessing and modifying labels value

var paybackLabel : UILabel = UILabel()
var paybackSlider : UISlider = UISlider()

2.) Put below code in viewDidload()

//Create Label

paybackLabel = UILabel(frame: CGRectMake(10, 20, 100, 41))
paybackLabel.center = CGPointMake(190, 61)
paybackLabel.textAlignment = NSTextAlignment.Center
paybackLabel.font = UIFont(name: paybackLabel.font.fontName, size:10)
paybackLabel.textColor = UIColor.blueColor()
paybackLabel.text = "Hello World"
self.view.addSubview(paybackLabel)

//Create Slider

paybackSlider = UISlider(frame: CGRectMake (45,70,310,31))
paybackSlider.minimumValue = 0
paybackSlider.maximumValue = 1000
paybackSlider.continuous = true
paybackSlider.tintColor = UIColor.blueColor()
paybackSlider.value = 500
paybackSlider.addTarget(self, action: "paybackSliderValueDidChange:",forControlEvents: .ValueChanged)
paybackLabel.text = "\(paybackSlider.value)"
self.view.addSubview(paybackSlider)

3.) Not put function which doing changes for displaying value on label by changing on slidervaluechanged event

func paybackSliderValueDidChange(sender: UISlider!)
{
    print("payback value: \(sender.value)")
    paybackLabel.text = "\(sender.value)"
}

Result :

Nows its work fine enjoy..

Answer 2

Globally Declare outside of ViewDidLoad()

     var  paybackLabel = UILabel()
     var paybackSlider = UISlider()

and Also don't forget to set userInteractionEnabled to true

   paybackLabel.userInteractionEnabled = true
    paybackSlider.userInteractionEnabled = true