android-studio - 分类器没有伴随对象

Question

我想在我的应用程序中使用 BottomNavigationView 并且我在使用 kotlin 时遇到了这个问题(以前从未在 java 中遇到过)我看到这条消息:
分类器“listFragment”没有伴随对象，因此必须在此处初始化

这是我的代码:

private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
    when (item.itemId) {
        R.id.listNav -> {
//the problem is here in listFragment word below
            setFragment(listFragment)
            return@OnNavigationItemSelectedListener true
        }
        R.id.accountNav -> {
//the problem is here also in accountFragment word below
            setFragment(accountFragment)
            return@OnNavigationItemSelectedListener true
        }
false 
}
private fun setFragment(fragment: Fragment) {
    supportFragmentManager.beginTransaction().replace(R.id.mainFrame , fragment).commit()
}

任何帮助表示赞赏:)

Answer 1

我以这种方式编辑它并且它起作用了:

private val mOnNavigationItemSelectedListener = BottomNavigationView.OnNavigationItemSelectedListener { item ->
    when (item.itemId) {
        R.id.listNav -> {
            val mFragment = cartFragment.newInstance()
            openFragment(mFragment)
            return@OnNavigationItemSelectedListener true
        }
        R.id.cartNav -> {
            val mFragment = cartFragment.newInstance()
            openFragment(mFragment)
            return@OnNavigationItemSelectedListener true
        }
        R.id.supportNav -> {
            val mFragment = supportFragment.newInstance()
            openFragment(mFragment)
            return@OnNavigationItemSelectedListener true
        }
        R.id.accountNav -> {
            val mFragment = accountFragment.newInstance()
            openFragment(mFragment)
            return@OnNavigationItemSelectedListener true
        }
    }
    false
}
private fun openFragment(fragment: Fragment) {
    val transaction = supportFragmentManager.beginTransaction()
    transaction.replace(R.id.mainFrame, fragment)
    transaction.addToBackStack(null)
    transaction.commit()
}

片段是这样的:

class listFragment : Fragment() {

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? =
        inflater.inflate(R.layout.fragment_list, container, false)

companion object {
    fun newInstance(): listFragment = listFragment()
}

}