backNavigation.kt

//back navigation in android 

//initate toolbar 
val detailsToolbar: Toolbar by lazy { findViewById<Toolbar>(R.id.toolbar) }

//in onCreate
this.setSupportActionBar(detailsToolbar)
actionBar = supportActionBar
actionBar?.apply {
    this.setDisplayHomeAsUpEnabled(true)
    this.setHomeButtonEnabled(true)
    this.setHomeAsUpIndicator(R.drawable.ic_back_dark)
}

// onOptionsItemSelected
override fun onOptionsItemSelected(item: MenuItem): Boolean {

    return when (item.itemId) {
        android.R.id.home -> {
            this.finish()
            true
        }
        else -> super.onOptionsItemSelected(item)
    }
}