Delegated Properties

By Syed Wahaj

Delegated properties are a powerful feature in Kotlin that allows us to simplify code, reduce boilerplate, and create more readable and maintainable code. In this article, we will explore the concept of delegated properties, how they work, and how to use them in our Kotlin projects.

Introduction to Delegated Properties

Delegated properties allow us to delegate the implementation of the property’s getter and setter methods to a separate class, which is responsible for managing the property’s value. This class is known as the delegate class, and it must implement a specific interface, depending on the type of delegation we want to perform.

Kotlin provides two types of delegated properties: lazy and observable. The lazy property is used to defer the initialization of the property until its first access, while the observable property is used to observe changes to the property’s value and perform some action whenever the value is updated.

Delegating Property Initialization using lazy

The lazy property delegate is used to defer the initialization of the property until its first access. This is useful when we want to initialize a property that is expensive to compute, such as a database connection or a network call.

To use the lazy delegate, we need to define the property as val and initialize it using a lambda expression that returns the initial value of the property. The lazy delegate is thread-safe, and the initialization of the property is performed only once.

val myProperty: String by lazy {
    // initialization code
}

Observing Property Changes using observable

The observable property delegate is used to observe changes to the property’s value and perform some action whenever the value is updated. This is useful when we want to perform some action whenever a property’s value changes, such as updating a UI element or logging the change.

To use the observable delegate, we need to define the property as var and initialize it with its initial value. We also need to define a lambda expression that is called whenever the property’s value is updated.

var myProperty: String by Delegates.observable("initial value") {
    property, oldValue, newValue ->
    // action to perform when the value is updated
}

In the lambda expression, property is a reference to the myProperty object, oldValue is the property’s previous value, and newValue is the property’s new value.

Conclusion

Delegated properties are a powerful feature in Kotlin that allows us to simplify code, reduce boilerplate, and create more readable and maintainable code. We explored the concept of delegated properties, how they work, and how to use them in our Kotlin projects. The lazy delegate is used to defer the initialization of the property until its first access, while the observable delegate is used to observe changes to the property’s value and perform some action whenever the value is updated. With delegated properties, we can write more concise and expressive code, which is easier to read and maintain.