Property delegation Examples

BackgroundColorAnimation.kt

fun backgroundColorAnimator(): ReadWriteProperty<View, Int> =
        object : ReadWriteProperty<View, Int> {

            override fun getValue(thisRef: View, property: KProperty<*>): Int {
                return (thisRef.background as? ColorDrawable)?.color ?: 0
            }

            override fun setValue(thisRef: View, property: KProperty<*>, value: Int) {

                ValueAnimator.ofObject(ArgbEvaluator(), getValue(thisRef, property), value).apply {
                    duration = 1000L
                    interpolator = AccelerateDecelerateInterpolator()
                    addUpdateListener { thisRef.setBackgroundColor(it.animatedValue as Int) }
                }.start()

            }

        }

//View ahora tiene una propiedad bgColor que si la cmabiamos animará el background de la vista de forma animada
var View.bgColor: Int by backgroundColorAnimator()

Invalidator.kt

fun <Param> View.invalidator(initialValue: Param, afterChangeBlock: ((Param) -> Unit)? = {}): ReadWriteProperty<Any?, Param> =
        object : ObservableProperty<Param>(initialValue) {
            override fun afterChange(property: KProperty<*>, oldValue: Param, newValue: Param) {
                afterChangeBlock?.invoke(newValue)
                this@invalidator.invalidate()

            }
        }

fun <Param> View.layoutRequester(initialValue: Param, afterChangeBlock: ((Param) -> Unit)? = {}): ReadWriteProperty<Any?, Param> =
        object : ObservableProperty<Param>(initialValue) {
            override fun afterChange(property: KProperty<*>, oldValue: Param, newValue: Param) {
                afterChangeBlock?.invoke(newValue)
                this@layoutRequester.requestLayout()

            }
        }

PropertyAnimation.kt

fun <Param : Number> View.propertyAnimator(initValue: Param, beforAnimationBlock: ((Param) -> Param)? = null): ReadWriteProperty<Any?, Param> =
        object : ReadWriteProperty<Any?, Param> {

            private var innerValue: Param = initValue
            private val persistedInitialValue = innerValue

            override fun getValue(thisRef: Any?, property: KProperty<*>): Param {
                return innerValue
            }

            @Suppress("UNCHECKED_CAST")
            override fun setValue(thisRef: Any?, property: KProperty<*>, value: Param) {

                val finalValue = beforAnimationBlock?.invoke(value) ?: value

                obtainValueAnimator(persistedInitialValue, finalValue).apply {
                    duration = 1500L
                    interpolator = BounceInterpolator()
                    addUpdateListener { innerValue = it.animatedValue as Param; invalidate() }
                }.start()
            }

            private fun obtainValueAnimator(innerValue: Param, value: Param): ValueAnimator {
                return when (innerValue) {
                    is Float -> ValueAnimator.ofFloat(innerValue, value.toFloat())
                    is Double -> ValueAnimator.ofFloat(innerValue.toFloat(), value.toFloat())
                    is Int -> ValueAnimator.ofInt(innerValue, value.toInt())
                    is Short -> ValueAnimator.ofInt(innerValue.toInt(), value.toInt())
                    is Long -> ValueAnimator.ofInt(innerValue.toInt(), value.toInt())
                    else -> ValueAnimator.ofFloat(innerValue.toFloat(), value.toFloat())
                }
            }

        }

Usages.kt

//estas propiedades están siendo definidas dentro de una View
var startingDegree: Int by invalidator(270)
var prefixText: String by layoutRequester("£")
var progress: Int by propertyAnimator(0)