CODEWITHSUNDEEP
iosswiftdoublescientific-notationuistepper
Brian
Brian

Reputation: 31282

UIStepper.value becomes scientific notation

This is my code:

@IBAction func stepperChanged(sender: AnyObject) {
    let stepper = sender as! UIStepper
    stepper.stepValue = 0.1
    stepper.minimumValue = 0.0
    stepper.maximumValue = 1.0
    print("stepper value: \(stepper.value)")
}

When I kept pressing the minus button, the output was:

stepper value: 0.2
stepper value: 0.1
stepper value: 1.38777878078145e-16
stepper value: 0.0

Why there was 1.38777878078145e-16 between 0.1 and 0.0?

I want to know the reason and how to fix it.

Thanks!

Upvotes: 0

Views: 249

Answers (2)

Sweeper
Sweeper

Reputation: 272035

Doubles are not precise.

The type of UIStepper.value is Double. And Doubles' precision is only 16 - 17 digits. This means that in this code, result is not equal to 0.1:

let a = 0.3
let b = 0.2
let result = a - b
// result might be 0.1000000000000000007890778643

So when you click the minus button, somewhere in the code there is this statement:

value -= stepValue

Since stepValue is also a Double, it is not precise. What is happening is that the step value might be equal to 0.9999999999999999138777878078145 when you click it the third time. Therefore, the stepper's value is not 0.

Another possible explanation would be that value is not accurate, it might be 0.1000000000000000861222121021854

Remember, programming is not math.

How to solve this problem?

So you want to disable the minus button when it is close to 0, right? It's easy!

if stepper.value - 0 < 0.0000001 {
    stepper.value = 0
}

Upvotes: 1

Alvin George
Alvin George

Reputation: 14296

Please try minimum value as 0 and maximum value as 10.

override func viewWillAppear(animated: Bool) {
        sampleUIStepper.minimumValue = 0
        sampleUIStepper.maximumValue = 10
        sampleUIStepper.stepValue = 1
    }

Convert the UIStepper's sender value to required format and use it.

@IBAction func sampleStepperValueChanged(sender: AnyObject) {
        let stepper = sender as! UIStepper

        let convertedValue = (stepper.value/10) as Double
        print(convertedValue)

    }

Upvotes: 4

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