将片段中视图上的click事件传递给活动

Question

class MoreFragment : Fragment() {

    internal var callback: OnMoreItemClickedListener

    fun setOnMoreItemClickedListener(callback: OnMoreItemClickedListener) {
        this.callback = callback
    }

    interface OnMoreItemClickedListener {
        fun onAddClothClicked()
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
    }

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        return inflater.inflate(R.layout.fragment_more, container, false)
    }

    override fun onActivityCreated(savedInstanceState: Bundle?) {
        super.onActivityCreated(savedInstanceState)
    }

    override fun onStart() {
        super.onStart()

        btn_add_clothes.setOnClickListener {
            callback.onAddClothClicked()
        }

    }
}

class MainActivity : AppCompatActivity(), MoreFragment.OnMoreItemClickedListener {

    override fun onAddClothClicked() {
        Log.d("MainActivity", "HERE")
    }

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        val navView: BottomNavigationView = findViewById(R.id.nav_view)

        val navController = findNavController(R.id.nav_host_fragment)
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        val appBarConfiguration = AppBarConfiguration(
            setOf(
                R.id.navigation_clothes,
                R.id.navigation_seasons,
                R.id.navigation_notifications,
                R.id.navigation_more
            )
        )
        setupActionBarWithNavController(navController, appBarConfiguration)
        navView.setupWithNavController(navController)
    }

    override fun onAttachFragment(fragment: Fragment) {
        super.onAttachFragment(fragment)

        if(fragment is MoreFragment){
            fragment.setOnMoreItemClickedListener(this)
        }
    }
}

MoreFragment.kt: (16, 5): Property must be initialized or be abstract

我尝试过的事情

• 我尝试为回调变量:onmoreItemClickedListener放一个lateInit var，但没有成功。因为它永远不会被初始化。
• 我将内部var回调：onmoreItemClickedListener？=null并使用null safe运算符引用了回调？。但无法获取click事件。

我是相当新的Kotlin和碎片太，所以请帮助我如何做到这一点。谢谢

Answer 1

在片段重写onAttach方法中

private lateinit var callback: OnMoreItemClickedListener

    override onAttach(context : Context){
    callback  = context as OnMoreItemClickedListener
    }

然后您的回调将是init。因为onAttach将是第一个。因此，没有属性必须初始化，否则将发生抽象错误。

同样，在活动中，实现您的接口（OnMoreItemClickedListener）并重写它的方法。你会得到回拨