Kotlin_Null_Safety.kt

Kotlin_Null_Safety.kt

package academy.learnprogramming.calculator

import android.support.v7.app.AppCompatActivity
import android.os.Bundle
import android.widget.EditText
import android.widget.TextView

class MainActivity : AppCompatActivity() {
    //varianta1
    //we tell kotlin that we're using a non-nullable variable, but that we'll delay giving it a value until later
    private lateinit var result:EditText
    private lateinit var newNumber: EditText

    //varianta2
    //when using by lazy, you're defining a function that will be called to asign a value to the property; the function will be called the first time the property is accessed, then the value is CACHED, so that the function isn't called again.
    //as long as we don't access displayOperation untill onCreate is called, this will work fine
    //avantajul e ca displayOperation poate fi declarat VAL, spre deosebire de lateinit care vrea doar VAR
    private val displayOperation by lazy {findViewById<TextView>(R.id.operation) }
    //the lazy function is thread-safe; if the displayOperation property is accessed by 2-3 threads simultaneously, the function will still only be called once

    //versiune modificata, because our activity class can't be accessed by more than one thread, so it's no need for the extra overhead that lazy includes by default (for multi-threads)
    //aka vom adauga inca un parametru to disable the tread-safe code, whenever we're using it IN AN ACTIVITY.
    private val displayOperation by lazy(LazyThreadSafetyMode.NONE) {findViewById<TextView>(R.id.operation) }


    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}