KObserve

An easy to use kotlin library for observable properties.

1. Quick start
2. Event handler
3. Properties
4. Observable lists

Quick start

To use this library simply add this to your build.gradle

repositories {
    jcenter()
}

dependencies {
    implementation "de.westermann:KObserve-jvm:$version"
}

To use it with javascript or common modules replace KObserve-jvm with KObserve-js or KObserve-metadata respectively.

When you use this library in common modules you need to add the platform specific dependency to each depending module.

An easier method is to enable gradle_metadata an experimental feature for gradle 5. This will automatically determine the target platform and include the necessary dependency.

Add this to your settings.gradle

enableFeaturePreview('GRADLE_METADATA')

And update your build.gradle

repositories {
    jcenter()
}

dependencies {
    implementation "de.westermann:KObserve:$version"
}

Event handler

val onRandomNumber = EventHandler<Int>()

onRandomNumber { number -> Int
    println("The random number is $number!")
}

onRandomNumber.emit(5)

For advanced usage you can obtain a event listener reference or combine event handlers.

val addedReference = onRandomNumber.reference {
    println("This listener can be removed easily.")
}
addedReference.remove()

val onFoo = EventHandler<Int>()
val onBar = EventHandler<Double>()

(onRandomNumber + onFoo) { number: Int ->
    println("The int is $number!")
}
onFoo.and<Number>(onFoo) { number: Number ->
    println("The number is $number!")
}

Properties

Create a simple object property with the property(T) function:

val numberProperty: ObjectProperty<Int> = property(0)
var number: Int by numberProperty

numberProperty.onChange {
    println("Number has been changed!")
}

number = 2

or use the observe() extension function:

val numberProperty: ObjectProperty<Int> = 0.observe()

You can map each property to observe a member property:

class Person(
    var name: String
)
val personProperty = Person("John Doe").observe()

val nameProperty = personProperty.map(Person::name)
var name: String by namePropery

or a computed value:

val nameLengthProperty = nameProperty.map { it.length }

Observable lists

val personList = observableListOf<Person>()

val mappedList = personList.mapObservable {
    it.name
}

val filteredList = personList.filterObservable {
    it.name.length > 5
}

val sortedList = personList.sortObservable(Comparator { p1, p2 -> 
    p1.name.compareTo(p2.name)
})

Math extension

val number1 = property(5)
val number2 = property(10)

val calcProperty = (number1 + number2) * number1