将 2 个片段的 Kotlin 代码合并为一个 class

Question

我有一个片段，我想在应用程序中有两次，但有细微的变化。有没有办法使用某种抽象 Class？我已经尝试自己找到解决方案，但我找不到使用委托属性从 Activity 获取 Viewmodel 的方法，因为 Android Studio 说这不能是抽象的。我面临的另一个问题是我传递给片段的参数。

（澄清一下：应该更改的属性是 Viewmodel；我想为第二个 Fragment 使用另一种 Viewmodel。此外，我在下面的代码中使用的 Viewmodel 和另一个Viewmodel 都继承自相同的 class，因此切换 Type 应该不是什么大问题）

片段代码如下：

package net.informatikag.thomapp.viewables.fragments.ThomsLine.main

import android.os.Bundle
import android.util.Log
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.fragment.app.activityViewModels
import androidx.lifecycle.Observer
import androidx.navigation.fragment.findNavController
import androidx.recyclerview.widget.LinearLayoutManager
import androidx.swiperefreshlayout.widget.SwipeRefreshLayout
import com.android.volley.*
import com.android.volley.toolbox.JsonArrayRequest
import com.android.volley.toolbox.Volley
import com.google.android.material.snackbar.Snackbar
import net.informatikag.thomapp.MainActivity
import net.informatikag.thomapp.R
import net.informatikag.thomapp.databinding.ThomslineMainFragmentBinding
import net.informatikag.thomapp.utils.handlers.WordpressRecyclerAdapter
import net.informatikag.thomapp.utils.ArticleListSpacingDecoration
import net.informatikag.thomapp.utils.models.ArticleClickHandler
import net.informatikag.thomapp.utils.models.data.WordpressArticle
import net.informatikag.thomapp.utils.models.data.WordpressPage
import net.informatikag.thomapp.utils.models.view.ThomsLineViewModel
import java.util.*
import kotlin.collections.ArrayList

/**
 * Pulls a list of articles from the JSON API of the Wordpress instance of the ThomsLine student newspaper.
 * The articles are dynamically loaded with a RecyclerView.
 */
class ThomsLineFragment : Fragment(), SwipeRefreshLayout.OnRefreshListener, ArticleClickHandler {

    private var _binding: ThomslineMainFragmentBinding? = null                  // Verweis zum Layout
    private val viewModel: ThomsLineViewModel by activityViewModels()   // Das Viewmodel in dem die wichtigen Daten des Fragments gespeichert werden
    private lateinit var recyclerAdapter: WordpressRecyclerAdapter              // Hier werden die Artikel angezeigt
    private lateinit var swipeRefreshLayout: SwipeRefreshLayout                 // wird benutz um die Artikel neu zu laden

    // This property is only valid between onCreateView and
    // onDestroyView.
    private val binding get() = _binding!!

    /**
     * Will be executed when the fragment is opened
     */
    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        // Inflate Layout
        _binding = ThomslineMainFragmentBinding.inflate(inflater, container, false)
        val root: View = binding.root

        //Instantiate Variables
        recyclerAdapter =  WordpressRecyclerAdapter(this, viewModel)

        //Add Observer to articles to update Recyclerview
        viewModel.articles.observe(viewLifecycleOwner, Observer {
            swipeRefreshLayout.isRefreshing = false
        })

        //region Init SwipeRefresh Layout
        swipeRefreshLayout = root.findViewById(R.id.thomsline_swipe_container)
        swipeRefreshLayout.setOnRefreshListener(this)
        swipeRefreshLayout.setColorSchemeResources(
            R.color.primaryColor,
            R.color.secondaryColor
        )

        if(viewModel.isEmpty()) {
            swipeRefreshLayout.post {
                // Display Refresh Indicator
                swipeRefreshLayout.isRefreshing = true
                // Load First Article Page
                loadArticles(0, true)
            }
        }
        //endregion

        //region Init Recycler View
        _binding?.thomslineRecyclerView?.apply {
            layoutManager = LinearLayoutManager(this@ThomsLineFragment.context)
            addItemDecoration(ArticleListSpacingDecoration())
            adapter = recyclerAdapter
        }
        //endregion

        return root
    }

    override fun onDestroyView() {
        super.onDestroyView()
        _binding = null
    }

    /**
     * Called when the SwipeRefresh Layout is triggerd
     */
    override fun onRefresh() {
        loadArticles(0, true)
    }

    /**
     * Loads all Article pages until "page" and removes all cached pages after it
     */
    fun loadArticles(page:Int, reloadAll: Boolean){
        // Remove all cached pages after the given one
        if(page == 0) {
            viewModel.removeArticlePagesFromIndex(1, recyclerAdapter)
            viewModel.lastPage = -1
        }

        // Create a new Request Queue
        val requestQueue = Volley.newRequestQueue(this.context)

        // Add requests to load the Pages to the requestQueue
        if(reloadAll)
            for (i in 0 until page+1) {
                reloadPage(i, requestQueue)
            }
        else reloadPage(page)
    }

    // Reload a page without a given Request Queue
    fun reloadPage(id:Int){
        reloadPage(id, Volley.newRequestQueue(this.context))
    }

    // Reload a Page while adding the Requests to a given Request Queue
    fun reloadPage(id: Int, requestQueue:RequestQueue) {
        Log.d("ThomsLine", "Requesting Data for page $id")

        // Start the Request
        requestQueue.add(JsonArrayRequest(viewModel.BASE_URL + MainActivity.WORDPRESS_BASE_URL_LITE + "&&page=${id+1}",
            { response ->
                Log.d("ThomsLine", "Got Data for page $id")

                // A Variable to load the Articles to
                val data = ArrayList<WordpressArticle>()

                // Load the Articles from the JSON
                for (j in 0 until response.length()) data.add(WordpressArticle(response.getJSONObject(j), true, viewModel.BASE_URL))

                // Update the RecyclerView
                viewModel.setArticlePage(id, WordpressPage(data.toTypedArray()), recyclerAdapter)

            },
            { volleyError ->
                Log.d("ThomsLine", "Request Error while loading Data for page $id")

                // Check if the Error is caused because loading a non Existing Page
                if (volleyError.networkResponse?.statusCode == 400){

                    // Update the Last Page Variable
                    viewModel.lastPage = if(id-1<viewModel.lastPage) viewModel.lastPage else id-1
                    recyclerAdapter.notifyItemChanged(recyclerAdapter.itemCount-1)
                    Log.d("ThomsLine", "Page does not exist (last page: ${viewModel.lastPage})")
                } else {
                    Log.d("ThomsLine", "Request failed: ${volleyError.message.toString()}")
                    // Display a Snackbar, stating the Error
                    Snackbar.make(requireActivity().findViewById(R.id.app_bar_main), WordpressArticle.getVolleyError(volleyError, requireActivity()), Snackbar.LENGTH_LONG).show()
                }

                //recyclerAdapter.notifyItemChanged(id)
            }
        ))
    }

    /**
     * Called when a Article is clicked
     */
    override fun onItemClick(wordpressArticle: WordpressArticle) {
        val action = ThomsLineFragmentDirections.actionNavThomslineToNavThomslineArticleView(wordpressArticle.id)
        findNavController().navigate(action)
    }
}

Answer 1

您没有在摘要 class 中分配 ViewModel（这是您使用委托 by activityViewModels() 所做的）。只需在您的摘要 class 中将其设为摘要属性，然后您的具体 Fragment 子 class 将被要求为其分配一个值（如果您愿意，可以使用 by activityViewModels() ):

abstract class BaseFragment : Fragment() {
    ...
    abstract val viewModel: BaseViewModel
    ...
}

class RealFragment : BaseFragment() {
    ...
    // you can specify a subtype of BaseViewModel in your implementation
    override val viewModel: SomeViewModel by activityViewModels()
    ...
}

将 2 个片段的 Kotlin 代码合并为一个 class

Combine Kotlin code of 2 fragments into one class

android

android-fragments

kotlin