getDeclaredField通过反射机制获取view

private void getTv() {
    BottomNavigationMenuView menuView = (BottomNavigationMenuView) bottomNavigationView.getChildAt(0);
    BottomNavigationItemView itemView = (BottomNavigationItemView) menuView.getChildAt(0);
    try {
        Field tv2 = itemView.getClass().getDeclaredField("largeLabel");
        tv2.setAccessible(true);
        TextView textView = (TextView) tv2.get(itemView); // 获取textView实例
        textView.setText("text4");
        textView.setVisibility(View.VISIBLE);
        tv2.set(itemView, textView);
    } catch (NoSuchFieldException | IllegalAccessException e) {
        e.printStackTrace();
    }
}

//反射viewpager

try {
                Class c = Class.forName("android.support.v4.view.ViewPager");
                Field field =c.getDeclaredField("mOffscreenPageLimit");
                field.setAccessible(true);
                field.setInt(this, limit);
                Class clazz = this.getClass();
                Method m1 = clazz.getDeclaredMethod("populate");
                m1.invoke(this);
            } catch (Exception e) {
                e.printStackTrace();
            }