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Sanjay Prajapat
Sanjay Prajapat

Posted on • Edited on • Originally published at sanjayprajapat.hashnode.dev

Delegated properties In Kotlin

#kotlin #delegation

Delegate is just class ,that help us to seperate all logic of getter and setters so it can be reused .
if want to use same code for more than one property ,then don't need to apply same code for every property ex:

/* dont need to write this code */ class User{ var firstName:String? =null set(value){ if(value!= null ) field = value.trim() } var lastName:String? = null set(value){ if(value!= null ) field = value.trim() } }
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use this code

class User{ var firstName:String? by TrimDelegate() var lastName:String? by TrimDelegate() // to print object  override fun toString():String{ return "$firstName $lastName" } }
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create custom Delegate class and name it TrimDelegate

class TrimDelegate { private var trimmedString:String ? = null // thisRef is calling object  operator fun setValue( thisRef:Any,property:KProperty<*>, value:String?){ // (thisRef as User).firstName // to access member  value?.let { trimmedString = it.trim() } } operator fun getValue(thisRef:Any, property:KProperty<*>):String?{ return trimmedString } }
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fun main(args: Array<String>) { val user1 = User() user1.firstName = " justin " user1.lastName = " Bieber " print(user1.firstName ) // justin  print("\n$user1")//justin Bieber }
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