kotlin.properties.ObservableProperty.kt Maven / Gradle / Ivy
/*
* Copyright 2010-2018 JetBrains s.r.o. and Kotlin Programming Language contributors.
* Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
*/
package kotlin.properties
import kotlin.reflect.KProperty
/**
* Implements the core logic of a property delegate for a read/write property that calls callback functions when changed.
* @param initialValue the initial value of the property.
*/
public abstract class ObservableProperty(initialValue: V) : ReadWriteProperty {
private var value = initialValue
/**
* The callback which is called before a change to the property value is attempted.
* The value of the property hasn't been changed yet, when this callback is invoked.
* If the callback returns `true` the value of the property is being set to the new value,
* and if the callback returns `false` the new value is discarded and the property remains its old value.
*/
protected open fun beforeChange(property: KProperty<*>, oldValue: V, newValue: V): Boolean = true
/**
* The callback which is called after the change of the property is made. The value of the property
* has already been changed when this callback is invoked.
*/
protected open fun afterChange(property: KProperty<*>, oldValue: V, newValue: V): Unit {}
public override fun getValue(thisRef: Any?, property: KProperty<*>): V {
return value
}
public override fun setValue(thisRef: Any?, property: KProperty<*>, value: V) {
val oldValue = this.value
if (!beforeChange(property, oldValue, value)) {
return
}
this.value = value
afterChange(property, oldValue, value)
}
}