android - 如何从 Adapter 设置 LiveData？

Question

我有两个 fragment :(1) 图书馆 fragment ，(2) 书籍 fragment

图书馆 fragment 通过 RecyclerView 显示所有可用的书籍。用户可以点击每个 RecyclerView 项目，这会将 LiveData 设置为相应的书籍。同时将打开 Book Fragment，并显示该书的内容。

我在库 fragment 的 RecyclerView.Adapter 内的 ViewHolder 类中设置了一个 onClickListener。因此，当单击一个项目时，将设置实时数据，然后通过导航组件导航到 Book fragment 。 Book Fragment 在实时数据上有一个观察者并显示它。

正如您在下面的代码中看到的，我正在将 viewmodel 实例传递给适配器，这是不正确的......？或者是吗？应该怎么做？

库 fragment 代码 fragment

class LibraryFragment : Fragment() {
    [...]
    private val model: SharedViewModel by activityViewModels()
    private lateinit var gridlayoutManager: GridLayoutManager
    private lateinit var thumbnailAdapter: ThumbnailAdapter
    private lateinit var thumbnailRecyclerView: RecyclerView
    private lateinit var selectedFolder: Uri

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        val view = layoutInflater.inflate(R.layout.fragment_thumbnail_viewer, container, false)
        initRecyclerView(view)
        view.allFolderPicker.setOnClickListener {
            pickFolder()
        }
        view.switchFragment.setOnClickListener {
            findNavController().navigate(R.id.action_allFoldersFragment_to_oneFolderFragment)
        }
        return view
    }

    private fun initRecyclerView(view: View) {
        thumbnailRecyclerView = view.findViewById(R.id.thumbnail_recycler_view)
        gridlayoutManager =
            GridLayoutManager(requireContext(), 3, LinearLayoutManager.VERTICAL, false)
        thumbnailRecyclerView.layoutManager = gridlayoutManager
        thumbnailAdapter = ThumbnailAdapter(model)
        thumbnailAdapter.setThumbnailList(listOf())
        thumbnailRecyclerView.adapter = thumbnailAdapter
    }
    [...]
}

适配器类代码 fragment

class ThumbnailAdapter(model: SharedViewModel) :
    RecyclerView.Adapter<ThumbnailAdapter.CustomViewHolder>() {

    private var thumbnailList = listOf<Pair<String, File>>()
    private val myModel = model

    inner class CustomViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        private val thumbnail = view.thumbnail
        private val title = view.title

        fun bind(item: Pair<String, File>) {
            val titleToSet = item.first
            val bitmapToSet = Util.uriToBitmap(item.second)
            val resizedBitmapToSet = Bitmap.createScaledBitmap(bitmapToSet, 150, 150, false)
            thumbnail.setImageBitmap(resizedBitmapToSet)
            title.text = titleToSet
            itemView.setOnClickListener {
                val folderWithImages = thumbnailList[adapterPosition].second.parentFile
                folderWithImages?.let {
                    myModel.setLibraryFolderList(it)
                    itemView.findNavController()
                        .navigate(R.id.action_allFoldersFragment_to_oneFolderFragment)
                }
            }
        }
    }
    [...]
}

书籍 fragment 代码 fragment

[...]

class BookViewFragment : Fragment() {

    private lateinit var viewPager: ViewPager2
    private lateinit var viewPagerAdapter: ViewPager2Adapter
    private val model: SharedViewModel by activityViewModels()


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

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        model.selectedBookFile.observe(viewLifecycleOwner, androidx.lifecycle.Observer {
            viewPagerAdapter.setImageList(getImageList(it))
            viewPagerAdapter.notifyDataSetChanged()
        })
    }

    private fun initRecyclerView(view: View) {
        viewPager = view.findViewById(R.id.main_image)
        viewPagerAdapter = ViewPager2Adapter()
        viewPagerAdapter.setImageList(listOf())
        viewPager.adapter = viewPagerAdapter
    }

    [...]
}

Answer 1

你不应该那样做，这里有一个关于 RecyclerView 的类(class)从显示到处理 clickListener。

他们是这样定义的:

While the ViewHolder is a great place to listen for clicks, it's not usually the right place to handle them. You should usually handle clicks in the ViewModel, because the ViewModel has access to the data and logic for determining what needs to happen in response to the click.

所以你应该这样做:

适配器:

class ThumbnailAdapter(model: SharedViewModel, val clickListener: ThumbnailListener) :
    RecyclerView.Adapter<ThumbnailAdapter.CustomViewHolder>() {

    private var thumbnailList = listOf<Pair<String, File>>()
    private val myModel = model

    override fun onBindViewHolder(holder: CustomViewHolder, position: Int) {
        val item = getItem(position)
        holder.itemView.setOnClickListener {
            listener.onClick(item)
        }
        holder.bind(marsProperty)
    }

    inner class CustomViewHolder(view: View) : RecyclerView.ViewHolder(view) {
        private val thumbnail = view.thumbnail
        private val title = view.title

        fun bind(item: Pair<String, File>) {
            val titleToSet = item.first
            val bitmapToSet = Util.uriToBitmap(item.second)
            val resizedBitmapToSet = Bitmap.createScaledBitmap(bitmapToSet, 150, 150, false)
            thumbnail.setImageBitmap(resizedBitmapToSet)
            title.text = titleToSet
        }
    }

    class ThumbnailListener(val clickListener: (libraryId: Long) -> Unit) {
        fun onClick(val library: Library) = clickListener(library.id)
    }

    [...]
}

View 模型:

private val _navigateToBook = MutableLiveData<Long>()
val navigateToBook: LiveData<Long>()
   get() = _navigateToBook

fun onLibraryClicked(libraryId: Long) {
    // your stuff
    _navigateToBook.value = libraryId
}

fragment :

thumbnailAdapter = ThumbnailAdapter(model, ThumbnailListener { libraryId ->
    viewModel.onLibraryClicked(libraryId)
})

viewModel.navigateToBook.observe(viewLifecycleOwner, Observer { book ->
    book?.let {
        this.findNavController().navigate(YOUR_DESTINATION)
    }
})

---

第二次使用数据绑定(bind)设置监听器的可能性:

xml 项目文件:

<data>

<variable
    name="listener"
    type="Your.Package.To.ThumbnailListener" />


</data>

<FrameLayout
    android:layout_width="match_parent"
    android:layout_height="170dp"
    android:onClick="@{() -> listener.onClick(property)}">

    ...

</FrameLayout>

适配器:

fun bind(item: Pair<String, File>, listener: ThumbnailListener) {
            val titleToSet = item.first
            val bitmapToSet = Util.uriToBitmap(item.second)
            val resizedBitmapToSet = Bitmap.createScaledBitmap(bitmapToSet, 150, 150, false)
            thumbnail.setImageBitmap(resizedBitmapToSet)
            title.text = titleToSet
            itemView.clickListener = listener
        }