what is delegation in kotlin

𝙲𝙾𝙽𝚃𝙴𝙽𝚃𝚂
What is meant by delegation
Using delegation with Lazy
Using delegation with Observable
Using delegation with Vetoable
Deligating objects
Property Deligation
Stop using base activity & use delegation

What is meant by delegation

• Delegation is an object-oriented pattern that helps in code reuse without using inheritance.
• Kotlin supports this natively.

Using delegation with Lazy

Using delegation with Observable

Using delegation with Vetoable

Deligating objects

Delegation in kotlin means, Delegating the responsibility to other objects.

Observation

• Notice in the place without using the by delegation we can observe there is more boiler code present.
• It is handled in Android by using the by keyword and as noticed, Significantly the boilerplate code is reduced.

Output

David is studying
<--------------->
David is studying

Code

fun main(args: Array<String>) {

    val david = David()
    val demoOne = SchoolDemoOne(david)
    val demoTwo = SchoolDemoTwo(david)

    demoOne.studying()
    println("<--------------->")
    demoTwo.studying()

}

/**
 * Studying can act studying
 */
interface Student {
    fun studying()
}


/**
 * Concrete implementation for a student
 */
class David : Student {
    override fun studying() {
        println("David is studying")
    }
}

/**
 * Delegation done but by not using `By` feature of kotlin
 */
class SchoolDemoOne(
    private val student : Student
): Student{
    override fun studying() {
        student.studying()
    }
}

/**
 * Delegation done but by using `By` feature of kotlin
 * Notice we removed the boilerplate code
 */
class SchoolDemoTwo(
    private val student : Student
): Student by student

Property delegation

• With the property delegation, We can override the getter and setter methods and easily be able to share this behavior.
• Basically once we override the properties, we can provide our own implementation that can be reused across multiple places where the same behavior is needed.
• Example

Stop using base activity & use delegation

• We used to use the base-activity to have some behavior for all our activities or some of the activities, For this kind of we needed the inheritance there.
• Well there is an alternative way of using inheritance, Well it is called delegation.
• Consider the use case
  • Say you have a functionality functionality-1 that you want to use in some activity --> You create a base activity and add that functionality. You can use this base activity as a parent with any of your children.
  • Say now you have a functionality functionality-2 that you want in some another activity --> You create another base activity and add that functionality. You again can use the base activity as a parent with children where you need.
  • Now if you want both functionality-1 and functionality-2 in some other scenario we might need a new base activity to be created
  • Use can use delegation to solve this.
• Demo