仅更改底部导航视图的一个图标的大小（Android）

我只想更改底部导航视图中使用的 5 个图标中的一个图标（第三个图标）的大小。

我想要中心图标像这样大：

这是我尝试过的：

private fun setReportPainIconSize(){
        val bottomNavigationView =
            findViewById<BottomNavigationView>(R.id.navigationBottomView)

    val menuView: BottomNavigationMenuView =
            bottomNavigationView.getChildAt(0) as BottomNavigationMenuView
     
    val iconView: View = menuView.getChildAt(2) **//TO GET REFERENCE OF 3RD ITEM**
                    .findViewById(androidx.core.R.id.icon)
           
    val layoutParams: ViewGroup.LayoutParams = iconView.layoutParams
            val displayMetrics: DisplayMetrics = resources.displayMetrics
            layoutParams.height = TypedValue.applyDimension(
                TypedValue.COMPLEX_UNIT_DIP, 47F,
                displayMetrics
            ).toInt()
            layoutParams.width = TypedValue.applyDimension(
                TypedValue.COMPLEX_UNIT_DIP, 44F,
                displayMetrics
            ).toInt()
            iconView.layoutParams = layoutParams
    }

但在运行我的应用程序时崩溃，我收到的错误消息是：

Caused by: java.lang.NullPointerException: menuView.getChildAt(2)
     …(androidx.core.R.id.icon) must not be null

我该如何实现它？ ？请帮忙！

使用最新的材料设计库(com.google.android.material:material:1.6.1)获取菜单图标视图引用的 id 是com.google.android.material.R.id.navigation_bar_item_icon_view. 

因此，您可以通过编程方式更改特定菜单项的大小BottomNavigationView像下面的示例：

//find the icon view for the menu item index 1
val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNavigationView)
val menu = bottomNavigationView.menu
val menuItem = menu.getItem(1)
val navigationBarItemView: NavigationBarItemView = bottomNavigationView.findViewById(menuItem.itemId)
val iconView: View = navigationBarItemView.findViewById(com.google.android.material.R.id.navigation_bar_item_icon_view)

//set the new width and height for the iconView in pixels. You can change also the bottom margin of the icon View.
val iconViewParams: FrameLayout.LayoutParams = iconView.layoutParams as FrameLayout.LayoutParams
iconViewParams.width = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 44F, resources.displayMetrics).toInt()
iconViewParams.height = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 47F, resources.displayMetrics).toInt()
iconViewParams.bottomMargin = TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 35F, resources.displayMetrics).toInt()
iconView.layoutParams = iconViewParams

还可以在上面画一些东西BottomNavigationView就像居中的图标一样，您必须将所有 ViewGroup 父级设置为BottomNavigationView具有clipChildren = false and clipToPadding = false使用如下递归函数：

fun recursiveClipChildrenAndClipToPadding(parent: ViewGroup) {

    if(parent is BottomNavigationView){
        val bottomNavigationView = parent as BottomNavigationView
        bottomNavigationView.clipChildren = false
        bottomNavigationView.clipToPadding = false
    }
    for (i in 0 until parent.childCount) {
        val child = parent.getChildAt(i)
        if (child is ViewGroup) {
            val vGroup = child as ViewGroup
            vGroup.clipChildren = false
            vGroup.clipToPadding = false
            recursiveClipChildrenAndClipToPadding(vGroup)
        }
    }
}

你必须这样称呼它：

recursiveClipChildrenAndClipToPadding(bottomNavigationView)

我使用一些默认图标制作的示例结果如下：