Delegation : By using Observable

Observation

• Notice in the output every time we modify the variable, It gives the oldValue and newValue.
• We can do something in the block when the value is accessed or modified.
• If we just access the variable, it will just return the value, and the block is not executed.
• Note we cannot reassign the variable inside the block.

Code

class MainActivity : ComponentActivity()
{

    private var demoObject by Delegates.observable(initialValue = 5) { property, oldValue, newValue ->
        println("OldValue:---> $oldValue")
        println("NewValue:---> $newValue")
    }
    
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

        demoObject = 8
        demoObject = 15

        setContent {}
    }
    
}

Output

OldValue:---> 5
NewValue:---> 8
OldValue:---> 8
NewValue:---> 15