使用正确的上下文

Question

需要在 SwipeToDeleteCallback 中的构造函数中粘贴上下文，它位于片段中：

private val swipeHandler = object : SwipeToDeleteCallback() {

    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
        presenter.removeListItem(viewHolder.adapterPosition)
    }
}

试图插入 requireContext() 但捕捉到 KotlinNullPointerException。

也许我可以在这里使用上下文 viewHolder.context?

这是一些代码 SwipeToDeleteCallback:

abstract class SwipeToDeleteCallback(context: Context) :
    ItemTouchHelper.SimpleCallback(0, ItemTouchHelper.LEFT or ItemTouchHelper.RIGHT) {

    private val deleteIcon = context.getDrawableCompat(R.drawable.ic_log_out)

我还从 MainActivity:

调用了我的片段

override fun onPostResume() {
    super.onPostResume()
    replaceFragment(TargetsFragment())
}

override fun showListOfTarget() {
    replaceFragment(TargetsFragment())
}

这是我的片段的完整代码：

class TargetsFragment : Fragment(), ListItemClickListener, SelectTargetViewContract, BaseDataSetContract {

    private var recyclerView: RecyclerView? = null
    private val presenter = TargetsPresenter(this)
    private var adapter = TargetsAdapter(clickListener = this)

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

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        presenter.setInitialData()
        setupViews()
        updateListData()
    }

    override fun onListItemClick(itemIndex: Int, itemCode: String) {
        presenter.onListItemClick((adapter.getItem(itemIndex) as Target).guid)
    }

    override fun showTarget(guid: String) {
        activity?.addFragment(TargetEditFragment.newInstance(guid))
    }

    override fun dataSetChanged() {
        updateListData()
        adapter.notifyDataSetChanged()
    }

    override fun updateViewContent() {
        adapter.data = presenter.targetList
        recyclerView?.adapter = adapter
        recyclerView?.setVisible(presenter.shouldShowContent())
        emptyView?.setVisible(presenter.shouldShowEmptyView())
    }

    private fun updateListData() {
        if (presenter.firebaseUser == null) {
            Log.d("some", "loadLogInView")
        } else {
            presenter.getTargetsFromDb()
        }
    }

    private val swipeHandler = object : SwipeToDeleteCallback() {

        override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {
            presenter.removeListItem(viewHolder.adapterPosition)
        }
    }

    private fun setupViews() {
        recyclerView = view?.findViewById(R.id.recyclerView)
        recyclerView?.layoutManager = LinearLayoutManager(activity)
        ItemTouchHelper(swipeHandler).attachToRecyclerView(recyclerView)
    }
}

Answer 1

您可以使用

yourViewHolder.itemView.context

获取yourViewHolder

的上下文

OP 澄清后：

最初我以为您只想从您的 ViewHolder 获取上下文，但这是我的答案的补充：

尝试将需要上下文的代码移动到 onAttach，您必须从文档中覆盖它：https://developer.android.com/guide/components/fragments.html

Caution: If you need a Context object within your Fragment, you can call getContext(). However, be careful to call getContext() only when the fragment is attached to an activity. When the fragment isn't attached yet, or was detached during the end of its lifecycle, getContext() returns null.

您正在寻找的方法如下所示：

override fun onAttach(context: Context) {
    super.onAttach(context)
}

您可以安全地将所有需要上下文的代码移入此方法并根据需要分配它

使用正确的上下文

Use right context

android

android-context

kotlin