使用 Model View Presenter 模式时如何实现 RecyclerView？

Question

我是第一次使用 MVP，我相信我明白了，但我不确定 RecyclerView。据我所知，MVP 是关于使视图尽可能被动，以便所有业务逻辑都转到 Presenter，但是如何为 Recycler View 实现这一点？

到目前为止，这是我的代码：

合同

public interface PhotosContract {
// View
interface View {//: IBaseActivity {
    fun showPhotos(photos: ArrayList<Photo>)
    fun showText(message: String)
}
// Presenter
interface Presenter {//: IBasePresenter<View> {
    fun getPhotos()
}
}

主持人

public class PhotosPresenter(var view: PhotosContract.View) :PhotosContract.Presenter {

var dataList = ArrayList<Photo>()

override fun getPhotos() {
    //call for endpoint
    val call : Call<ArrayList<Photo>> = ApiClient.getClient.getPhotos()

    call.enqueue(object: Callback<ArrayList<Photo>> {
        override fun onFailure(call: Call<ArrayList<Photo>>, t: Throwable) {
            Log.d("FAIL","FAILED")
        }

        override fun onResponse(
            call: Call<ArrayList<Photo>>,
            response: Response<ArrayList<Photo>>
        )
        {
            Log.d("SUCCESS","SUCCESSED")

            dataList.addAll(response!!.body()!!)
            Log.d("SIZELIST",dataList.size.toString())

            view.showPhotos(dataList)
            view.showText("SUCCESS")
        }

    })

}

}

RecyclerViewAdapter

class PhotosAdapter(private var dataList: List<Photo>, private val context: Context) : RecyclerView.Adapter<PhotosAdapter.PhotosViewHolder>() {

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): PhotosAdapter.PhotosViewHolder {
    return PhotosViewHolder(LayoutInflater.from(this.context).inflate(R.layout.list_item_home, parent, false))
}

override fun getItemCount(): Int {
    return dataList.size
}

override fun onBindViewHolder(holder: PhotosAdapter.PhotosViewHolder, position: Int) {
    val dataModel = dataList[position]
    holder.titleTextView.text = dataModel.title
}

class PhotosViewHolder(itemLayoutView: View) : RecyclerView.ViewHolder(itemLayoutView){
    var titleTextView: TextView = itemLayoutView.tv_title
}

}

Activity

class PhotosActivity : AppCompatActivity(),PhotosContract.View {
private lateinit var presenter: PhotosPresenter

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_photos)

    presenter = PhotosPresenter(this)

    presenter.getPhotos()

}

override fun showPhotos(photos: ArrayList<Photo>) {
    photosRecyclerView.layoutManager = LinearLayoutManager(this)
    photosRecyclerView.adapter = PhotosAdapter(photos,this)

    photosRecyclerView.adapter?.notifyDataSetChanged()
}

override fun showText(message: String) {
    Toast.makeText(this,message,Toast.LENGTH_LONG).show()
}


 }

Answer 1

下面是我在使用 MVP 时的做法。在您的合同中，定义一个名为 ItemView 的附加视图。我这样做的方式是，每个项目视图持有者都是一个 MVP 视图。视图是愚蠢的，所以它只是在有事情发生时调用演示者，然后演示者回调它。

interface MyContract {

    interface View {
        fun setTitle(title: String)
    }

    // Add this interface here
    interface ItemView {
        fun bindItem(item: Item)
    }

    interface Presenter {
        fun attach(view: View)
        fun detach()

        val itemCount: Int
        fun onItemClicked(pos: Int)
        fun onBindItemView(itemView: ItemView, pos: Int)
    }
}

适配器也很笨。当它需要绑定一个 item view holder 时，它会调用 presenter 来完成它。

class MyAdapter : RecyclerView.Adapter<ViewHolder>() {

    // How many items do we have? We don't know, ask the presenter.
    override fun getItemCount() = presenter?.itemCount ?: 0

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        // How to bind the item if we only have position? We don't know, ask the presenter.
        presenter?.onBindItemView(holder, position)
    }

    // ...
}

ViewHolder实现了MyContract.ItemView接口。同样，这只是一种观点，因此它本身不承担任何责任。它只是委托给演示者。

class MyViewHolder(itemView: View) : RecyclerView.ViewHolder(itemView), MyContract.ItemView {

    private val txv: TextView = view.findViewById(R.id.text_view)

    init {
        view.setOnClickListener {
            // What to do here, we only have the item's position? Call the presenter.
            presenter?.onItemClicked(adapterPosition)
        }
    }

    override fun bindItem(item: Item) {
        txv.text = item.text
    }
}

最后是主持人：

class MyPresenter : MyContract.Presenter {

    private var view: View? = null

    private val items = mutableListOf<Item>()

    override fun attach(view: View) {
        this.view = view
        // ...
    }

    override fun detach() {
        view = null
    }

    override val itemCount: Int
        get() = items.size

    override fun onItemClicked(pos: Int) {
        val item = items[pos]
        // ...
    }

    override fun onBindItemView(itemView: ItemView, pos: Int) {
        itemView.bindItem(items[pos])
    }

    // ...
}

完整性的观点，但这里没有新内容：

class MyView : Fragment(), MyContract.View {

    private var presenter: Presenter? = null

    override fun onViewCreated(view: View) {
        // Attach presenter
        presenter = MyPresenter()
        presenter?.attach(this)
    }

    override fun onDestroyView() {
        super.onDestroyView()

        // Detach the presenter
        presenter?.detach()
        presenter = null
    }

    // ...
}

这只是一种方法，我相信还有很多其他方法。我只是喜欢这个，因为所有的责任都属于演示者，其他任何地方都没有业务逻辑。

最终，您需要更改列表并通知适配器。为此，在您的 View 合同中添加几个方法，例如 notifyItemInserted(pos: Int) 并在演示者需要时调用它们。或者，更好的是，使用 DiffUtil 这样您就不必自己管理它了！

一旦你对 MVP 有了很好的理解，我强烈建议你转向 MVVM，因为它是 Google 推广的官方架构。大多数人也觉得它比 MVP 方便很多。

如果您有任何问题，请不要犹豫。

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