By - delegates basic learning

ByDelegateFragment.kt

package com.example.coroutinelearning.fragments

import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import com.example.coroutinelearning.databinding.ByDelegateLearningBinding

class ByDelegateFragment : Fragment() {

    private val TAG = ByDelegateFragment::class.simpleName
    private lateinit var binding: ByDelegateLearningBinding

    private val taxCollector = TaxCollector()
    private val accountant: Accountant by lazy { //one way
        Accountant()
    }

    //another way-> if you initialize delegate in such way, surchargeTaxDelegate.isInitialized() will be available
    private val surchargeTaxDelegate = lazy {
        SurchargeTax()
    }
    private val surchargeTax by surchargeTaxDelegate
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
    ): View? {
        binding = ByDelegateLearningBinding.inflate(inflater, container, false)
        return binding.root
    }

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        salaryTaxExample()
    }

    private fun salaryTaxExample() {
        Log.i(TAG, "Is Surcharge initialized ${surchargeTaxDelegate.isInitialized()}")
        val THRESHOLD = 80
        val salaries = listOf(50, 100, 70, 120) //salary in k -> 1000
        for (salary in salaries) {
            taxCollector.taxCalculation(salary)
            if (salary > THRESHOLD) {
                accountant.accountantDetail()
                surchargeTax.surchargeDeduction()
                Log.i(TAG, "Is Surcharge initialized ${surchargeTaxDelegate.isInitialized()}")
            }
        }
    }
}

class SurchargeTax {
    private val TAG = "ByDelegateFragment"

    init {
        Log.i(TAG, "SurchargeTax class is initialized")
    }

    fun surchargeDeduction() {
        Log.i(TAG, "Surcharge deduction function")
    }
}

class Accountant {
    private val TAG = "ByDelegateFragment"

    init {
        Log.i(TAG, "Accountant class is initialized")
    }

    fun accountantDetail() {
        Log.i(TAG, "accountantDetail function")
    }

}

class TaxCollector {
    private val TAG = "ByDelegateFragment"

    init {
        Log.i(TAG, "TaxCollector class is initialized")
    }

    fun taxCalculation(salary: Int = 0) {
        Log.i(TAG, "taxcalculation method, salary: $salary")
    }
}

logfile

2023-07-05 14:45:41.329 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: TaxCollector class is initialized
2023-07-05 14:45:41.360 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: Is Surcharge initialized false
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: taxcalculation method, salary: 50
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: taxcalculation method, salary: 100
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: Accountant class is initialized
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: accountantDetail function
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: SurchargeTax class is initialized
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: Surcharge deduction function
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: Is Surcharge initialized true
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: taxcalculation method, salary: 70
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: taxcalculation method, salary: 120
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: accountantDetail function
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: Surcharge deduction function
2023-07-05 14:45:41.361 5548-5548/com.example.coroutinelearning I/ByDelegateFragment: Is Surcharge initialized true

readfile

https://www.youtube.com/watch?v=tT7pQjSv-kc


The most common usage of delegated property in my opinion is by lazy.
I personally prefer val over var. So I use by lazy a lot whenever is possible instead of using lateinit var

use by lazy if creating any class or anything is costly or might be raerly used. so keep it with by delegate.