Mobile Master SharedPref

package com.example.programmingmasterandroid

import android.content.Context
import android.content.Intent
import android.os.Bundle
import android.support.v7.app.AppCompatActivity
import android.widget.Toast
import kotlinx.android.synthetic.main.login_layout.*

class Login: AppCompatActivity() {

    private var editUsername : String = ""
    private var editPassword : String = ""

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

        val sharedPref = applicationContext.getSharedPreferences(SharedPref.login, Context.MODE_PRIVATE) ?: return

        if (sharedPref.getString(SharedPref.username, SharedPref.defValueString) != SharedPref.defValueString &&
                sharedPref.getString(SharedPref.password, SharedPref.defValueString) != SharedPref.defValueString) {

            startActivity(Intent(this, MainActivity::class.java))
        } else {
            login_btn.setOnClickListener {

                editUsername = username.text.toString()
                editPassword = password.text.toString()

                if (checkKosong(editUsername, editPassword)) {
                    if (checkLogin(editUsername, editPassword)) {
                        with(sharedPref.edit()) {
                            putString(SharedPref.username, editUsername).apply()
                            putString(SharedPref.password, editPassword).apply()
                        }
                        startActivity(Intent(this, MainActivity::class.java))
                    } else {
                        Toast.makeText(applicationContext, "Username Dan Password Salah", Toast.LENGTH_LONG).show()
                    }
                } else {
                    Toast.makeText(applicationContext, "Isi Dahulu Username Dan Password", Toast.LENGTH_LONG).show()
                }

            }
        }
    }

    private fun checkKosong(username: String, password: String) : Boolean{
        if (username.isEmpty() && password.isEmpty()) {
            return false
        }
        return true
    }

    private fun checkLogin(username: String, password: String) : Boolean{
        if (username == "admin" && password == "admin"){
            return true
        }
        return false
    }
}