Can't use custom getter with delegated property

Question

I am new to kotlin and can't figure out this issue.

I have a property that is not nullable and may or may not be used. Hence I have delegated it in a lazy way so that it is initialized when required.

private val labelAnimator: ObjectAnimator by lazy {
    ObjectAnimator.ofFloat(this, "floatingLabelFraction", 0f, 1f)
}

However, I also need to set some property of that object every time it is accessed.

fun getLabelAnimator(): ObjectAnimator {
    labelAnimator.duration = (if (isFloatingLabelAnimating) 300 else 0).toLong()
    return labelAnimator
}

But I cannot use a custom getter since the property is delegated. How do I achieve this in best possible way?

While this does not answer your question, I would strongly advise against mutating a property in a getter. It violates the principle of least surprise. — Christian Brüggemann, Sep 01 '17 at 12:14

score 5 · Accepted Answer · answered Sep 01 '17 at 14:31

You could for example use your original property as Backing Property and actually define the property as a delegation to it.

private val _labelAnimator by lazy {
    ObjectAnimator.ofFloat(this, "floatingLabelFraction", 0f, 1f)
}

val labelAnimator: ObjectAnimator
    get() {
        _labelAnimator.duration = if (isFloatingLabelAnimating) 300L else 0L
        return _labelAnimator
    }

This gives you a getLabelAnimator() method in Java and direct property access in Kotlin.

But like it was stated several times before, it might not be the best way to implement such behavior. A simple factory could do the same with little overhead.

Bozic Nebojsa · Answer 2 · 2017-09-01T12:27:44.713

0

I am not a Kotlin expert, but it sounds wrong to me. By delegating to lazy you want to init object on its first getter call. And then, you are trying to write custom getter. I see a conflict there.

Maybe:

private val labelAnimator: ObjectAnimator by lazy {
    val labelAnimator = ObjectAnimator.ofFloat(this, "floatingLabelFraction", 0f, 1f)
    labelAnimator.duration = (if (isFloatingLabelAnimating) 300 else 0).toLong()
    labelAnimator
}

edited Sep 01 '17 at 12:27

answered Sep 01 '17 at 12:14

Bozic Nebojsa

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Wouldn't it create a new object every time I access the property? – Pramod Garg Sep 01 '17 at 12:18

score 0 · Answer 3 · answered Dec 22 '18 at 07:43

0

The shortest version

private val labelAnimator: ObjectAnimator by lazy {
    ObjectAnimator.ofFloat(this, "floatingLabelFraction", 0f, 1f).apply {
        duration = if (isFloatingLabelAnimating) 300L else 0L
    }
}

answered Dec 22 '18 at 07:43

Vlad

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Can't use custom getter with delegated property

3 Answers3

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