android – Change textSize of BottomNavigationView item

Why does BottomNavigationView have XML attributes like itemTextColor but noitemTextSize?

J & # 39; would:

A) Change the default text size of each element of my background navigation

B) Change the text size of an item after being clicked (ie how can I access the text size in onNavigationItemSelected ()?

The reason I ask the question is because I try to prevent having a selected element at first (the default is that the first element is checked):

replace fun onCreate (savedInstanceState: Bundle?) {
bottomNav_main.menu.getItem (0) .isCheckable = false
}

replace fun onNavigationItemSelected (element: MenuItem): Boolean {
item.isCheckable = true
returns true
}

However, the code above only prevents the first item from being checked. Color. He always checked text size (a little bigger than the uncontrolled text size).

An idea of ​​how I can solve this problem?