Question

我是Kotlin的新手。我有两个类，一个适配器和一个片段。当我想在片段中调用适配器类时，收到以下警告：cannot create an instance of the abstract class in Kotlin。

在我收到警告的片段下面

class FavouriteExercisesFragment : BaseMvpFragment(), FavoriteExerciseView {

    var adapter: FavoriteExerciseAdapter = FavoriteExerciseAdapter()
   // cannot create instance of abstract class in kotlin

在抽象适配器类之下

class FavouriteExercisesFragment : BaseMvpFragment(), FavoriteExerciseView {

    var adapter: FavoriteExerciseAdapter = FavoriteExerciseAdapter()
    val presenter: FavoriteExercisePresenter = FavoriteExercisePresenter(this)

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

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        initToolbar()
        initList()
        presenter.getFavoriteExercise()
    }

    private fun initList() {
        rvExercise.layoutManager = LinearLayoutManager(context)
        rvExercise.adapter = adapter
        val helper = ItemTouchHelper(object : ItemTouchHelper.SimpleCallback(ItemTouchHelper.UP or ItemTouchHelper.DOWN, ItemTouchHelper.RIGHT) {
            override fun onMove(recyclerView: RecyclerView?, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
                adapter.onItemMove(viewHolder.adapterPosition, target.adapterPosition)
                return true
            }

            override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
                val position = viewHolder.adapterPosition
                val item = adapter.data[position]
                adapter.onItemDismiss(viewHolder.adapterPosition)
                presenter.deleteFromFavorite(item, position)
                showEmptyData(adapter.data.isEmpty())

            }
        })
        rvExercise.addItemDecoration(object : RecyclerView.ItemDecoration() {
            override fun getItemOffsets(outRect: Rect, view: View?, parent: RecyclerView, state: RecyclerView.State?) {
                super.getItemOffsets(outRect, view, parent, state)
                val position = parent.getChildAdapterPosition(view)
                if (position == 0) {
                    outRect.top = 58.dp
                } else {
                    outRect.top = 0
                }

            }
        })
        helper.attachToRecyclerView(rvExercise)
        adapter.helper = helper
        adapter.actions = object : FavoriteExerciseAdapter.AdapterAction {
            override fun playExercise(exercise: Exercise) {
                val file = exercise.files.firstOrNull { it.mainFile }
                val uri = file?.getFile() ?: ""

                context?.startActivityFromCenter(VideoActivity.newInstance(context, uri), rootView, VideoActivity.REQUEST_CODE)
            }
        }
    }

    private fun initToolbar() {
        toolbar.setOnNavigateIconClickListener { router.exit() }
        toolbar.setOnToolIconClickListener { openNavDrawer() }
    }

    override fun setFavoriteExercises(exercises: ArrayList<Exercise>) {
        showEmptyData(exercises.isEmpty())
        adapter.addData(exercises)
    }

    override fun showDeleteMessage(item: Exercise, position: Int) {
        val snack = Snackbar.make(rootView, R.string.message_remove_from_favorite, Snackbar.LENGTH_LONG)
        snack.setAction(R.string.action_undo) {
            presenter.addToFavorite(item)
            adapter.addItemOnPosition(item, position)
            showEmptyData(adapter.data.isEmpty())
        }
        snack.show()
    }

    private fun showEmptyData(show: Boolean) {
        tvEmpty.visibility = if (show) View.VISIBLE else View.GONE
        emptyIcon.visibility = if (show) View.VISIBLE else View.GONE
    }
}

Answer 1

您无法创建抽象类的实例。您应该从类声明中删除摘要，或者应该创建扩展该抽象类的新类并创建该类的实例。

Answer 2

根据您的问题，我可以猜测FavoriteExerciseAdapter是抽象的。您需要在项目中添加一个新的具体类，例如将其命名为MyFavoriteExerciseAdapter。 MyFavoriteExerciseAdapter必须扩展FavoriteExerciseAdapter并覆盖FavoriteExerciseAdapter的所有抽象方法，现在实例化MyFavoriteExerciseAdapter而不是FavoriteExerciseAdapter：

var adapter: FavoriteExerciseAdapter = MyFavoriteExerciseAdapter()// instantiate MyFavoriteExerciseAdapter

我无法在Kotlin警告中创建抽象类的实例？

2 个答案: