Recyclerview 数据集在片段开始时不会改变

Posted 2023-04-19

【中文标题】Recyclerview 数据集在片段开始时不会改变

【英文标题】：Recyclerview dataset does not change on fragment start

【发布时间】：2021-09-26 09:33:04

【问题描述】：

我的片段上有一个 RecyclerView，它从名为 Datasource 的对象中的 ArrayList 获取数据。我想在 Fragment 启动时从 Cloud Firestore 获取新项目，所以我创建了一个名为 getAllProducts 的函数，但是我只能在单击底部导航栏时获取项目。

我几乎尝试了另一个问题的所有答案。我尝试在 onCreate 上重新加载片段，我创建了一个导航动作来片段本身，我在 RecyclerView 适配器中添加了一个从 getAllProducts 函数和 notifyDataSetChanged() 获取数据的函数。我让 getAllProduct 返回数组列表并将其用作 RecyclerView 中的数据。他们都没有工作。

应用启动时：

点击主页时：

这里有相关代码

ProductAdapter.kt

class ProductAdapter(private val productList: ArrayList<ProductItem>):RecyclerView.Adapter<ProductViewHolder>() 

    inner class ProductViewHolder(itemView:View):RecyclerView.ViewHolder(itemView)
        val productImage: ImageView = itemView.findViewById(R.id.productPhoto)
        val productName: TextView = itemView.findViewById(R.id.productName)
        val productRatingBar: RatingBar = itemView.findViewById(R.id.ratingBar2)
        val productRating: TextView = itemView.findViewById(R.id.ratingint)
        val storeName: TextView = itemView.findViewById(R.id.productStoreName)
        val productPrice: TextView = itemView.findViewById(R.id.productPrice)

    



    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder 

        val itemView = LayoutInflater.from(parent.context).inflate(R.layout.product_item,
        parent,false)

        return ProductViewHolder(itemView)
    

    override fun onBindViewHolder(holder: ProductViewHolder, position: Int) 
        val currentItem = productList[position]
        holder.itemView.setOnClickListener 
                view ->
            val action = ProductFragmentDirections.actionProductFragmentToParticularProductFragment2(currentItem)
            view.findNavController().navigate(action)
        
        holder.productImage.setImageResource(currentItem.productImageResource)
        holder.productName.text = currentItem.productName
        holder.productRatingBar.rating = currentItem.productRating.toFloat()
        holder.productRating.text = currentItem.productRating.toString()
        holder.storeName.text = currentItem.storeName
        holder.productPrice.text = currentItem.productPrice.toString().plus("$")

    


    override fun getItemCount() = productList.size

数据源.kt

object Datasource 

    var productList = arrayListOf(

        ProductItem(R.drawable.attach_money,"Sahibinden aerator",4.5,"Serhat Yilmaz",8),
        ProductItem(R.drawable.email,"dus kitapları",3.0,"nerhat Yilmaz",9),
        ProductItem(R.drawable.passwordicon,"h files",1.5,"berhat Yilmaz",77),
        ProductItem(R.drawable.category,"piyasemen",5.0,"xerhat Yilmaz",55),
        ProductItem(R.drawable.attach_money,"Sahibinden sasfaf",1.5,"kerhat Yilmaz",11),
        ProductItem(R.drawable.email,"tus kitapları",3.0,"uerhat Yilmaz",21),
        ProductItem(R.drawable.passwordicon,"f files",1.5,"yerhat Yilmaz",47),
        ProductItem(R.drawable.category,"anguldruva",2.0,"terhat Yilmaz",35),
        ProductItem(R.drawable.email,"tus2 kitaplarım",3.0,"werhat Yilmaz",78),
        ProductItem(R.drawable.passwordicon,"endobox",2.5,"Zerhat Yilmaz",95),
        ProductItem(R.drawable.category,"basplak",4.0,"Ferhat Yilmaz",12)

    )

    fun loadProduct(): ArrayList<ProductItem>
        return productList
    

ProductFragment.kt

class ProductFragment : Fragment() 
    private val myDataset = Datasource.productList
    private val adapter = ProductAdapter(myDataset)



    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? 


        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.products_fragment, container, false)
    

    override fun onViewCreated(view: View, savedInstanceState: Bundle?) 
        super.onViewCreated(view, savedInstanceState)


        val recyclerView: RecyclerView = view.findViewById(R.id.recycler_product)
        recyclerView.adapter = adapter
        recyclerView.layoutManager = LinearLayoutManager(requireActivity())
        FireStoreClass().getAllProducts()
        adapter.notifyDataSetChanged()

    

FireStoreClass().getAllProducts()

private val mFireStore = FirebaseFirestore.getInstance()

fun getAllProducts() 


    mFireStore.collection(Constants.PRODUCTS)
        .get()
        .addOnSuccessListener 
            documents ->
            val list = arrayListOf<ProductItem>()
            for (document in documents)

                val product = document.toObject(ProductItem::class.java)
                list.add(product)

            
            Datasource.productList = list
            
        .addOnFailureListener 
            //Toast.makeText(activity, "Can not get Product! $it.message", Toast.LENGTH_SHORT).show()
        

如果您需要查看：

NavigateActivity.kt

class NavigateActivity : AppCompatActivity() 
    private lateinit var navController: NavController
    override fun onCreate(savedInstanceState: Bundle?) 
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_navigate)
        val navHostFragment = supportFragmentManager.findFragmentById(R.id.nav_host_fragment) as NavHostFragment
        navController = navHostFragment.findNavController()
        val bottomNavigationView = findViewById<BottomNavigationView>(R.id.bottomNavView)
        bottomNavigationView.setupWithNavController(navController)
        //val action = HomeFragmentDirections


    

mobile_navigation.xml

<?xml version="1.0" encoding="utf-8"?>
<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/mobile_navigation"
    app:startDestination="@id/product_Fragment">

    <fragment
        android:id="@+id/product_Fragment"
        android:name="com.example.TheDentalSupplies.fragments.ProductFragment"
        android:label="products_fragment"
        tools:layout="@layout/products_fragment" >

        <action
            android:id="@+id/action_productFragment_to_particularProductFragment2"
            app:destination="@id/particularProductFragment" />

        <action
            android:id="@+id/action_productFragment_Reload"
            app:destination="@id/product_Fragment" />



    </fragment>
    <fragment
        android:id="@+id/addPostNavActivity"
        android:name="com.example.TheDentalSupplies.AddActivity"
        android:label="addpost"
        tools:layout="@layout/addpost" >
        <action
            android:id="@+id/action_addPostNavActivity_to_productFragment"
            app:destination="@id/product_Fragment" />
    </fragment>

    <activity
        android:id="@+id/userActivity"
        android:name="com.example.TheDentalSupplies.UserActivity"
        android:label="userlayout"
        tools:layout="@layout/userlayout" />
    <fragment
        android:id="@+id/bucketFragment"
        android:name="com.example.TheDentalSupplies.fragments.BucketFragment"
        android:label="bucketlayout"
        tools:layout="@layout/bucketlayout" />
    <fragment
        android:id="@+id/particularProductFragment"
        android:name="com.example.TheDentalSupplies.fragments.ParticularProductFragment"
        android:label="product_layout"
        tools:layout="@layout/product_layout">
        <argument
            android:name="navProductItem"
            app:argType="com.example.TheDentalSupplies.models.ProductItem" />
        <action
            android:id="@+id/action_to_bucketFragment"
            app:destination="@id/bucketFragment" />
        <action
            android:id="@+id/action_to_messageActivity"
            app:destination="@id/messageActivity" />
        <action
            android:id="@+id/action_feedbacksFragment2"
            app:destination="@id/feedbacksFragment2" />
    </fragment>
    <activity
        android:id="@+id/messageActivity"
        android:name="com.example.TheDentalSupplies.MessageActivity"
        android:label="messagelayout"
        tools:layout="@layout/messagelayout" />
    <fragment
        android:id="@+id/feedbacksFragment2"
        android:name="com.example.TheDentalSupplies.fragments.FeedbacksFragment"
        android:label="feedbacks_layout"
        tools:layout="@layout/feedbacks_layout" />

</navigation>

【参考方案1】：

Firebase API 是异步的。因此，任何需要来自数据库的数据的代码都需要在 onSuccess() 方法中，或者从那里调用。在此方法中分配list 对象：

Datasource.productList = list

并不意味着它会立即分配它。数据加载完成后调用 getAllProducts() 方法后始终会触发此代码。因此，您拥有的最佳选择是像这样创建以下对象：

private val myDataset = Datasource.productList
private val adapter = ProductAdapter(myDataset)

在onViewCreated里面：

val recyclerView: RecyclerView = view.findViewById(R.id.recycler_product)
recyclerView.layoutManager = LinearLayoutManager(requireActivity())
recyclerView.adapter = adapter
FireStoreClass().getAllProducts()

在 getAllProducts() 方法中，只需执行以下操作：

fun getAllProducts() 
    mFireStore.collection(Constants.PRODUCTS)
        .get()
        .addOnSuccessListener  documents ->
            for (document in documents)
                val product = document.toObject(ProductItem::class.java)
                myDataset.add(product)

            
            adapter.notifyDataSetChanged()
        .addOnFailureListener 
            Toast.makeText(activity, "Can not get Product! $it.message", Toast.LENGTH_SHORT).show()
        

这意味着只有当您从数据库中获得所有必要的数据时才通知适配器。

由于您使用的是 Kotlin，我想您可能也对这篇文章感兴趣：

How to read data from Cloud Firestore using get()?

【讨论】：

非常感谢您的回答。但它仍然不会在应用启动时加载产品。我应该在哪里添加 FireStoreClass().getAllProducts() ？由于我的英语不太好，希望我没有错过您的回答。

哦，对不起，我的错。只是忘了添加 FireStoreClass().getAllProducts() 。请检查我更新的答案。顺便说一句，你的英语真的很好;)

不幸的是它没有工作。应用程序启动时仍然不加载，我不知道为什么。感谢您的回答。祝你有美好的一天:)

“它不起作用”没有提供足够的信息，所以我可以进一步帮助您。 onFailure 中的 Toast 消息是否显示了什么？您是否尝试将 onViewCreated 上的四行代码移至 onCreateView 内？是这样的吗？

当我向 onCreateView 添加四行时，我得到了这个错误 java.lang.IllegalStateException: Fragment ProductFragment1336db9 (0bd85290-7fbe-4464-89cf-046e81c43e07 id=0x7f0a0162) did not return a View来自 onCreateView() 或在 onCreateView() 之前调用。

【参考方案2】：

我终于找到了一种方法，虽然不是最好的解决方案，但却能胜任。

常量.kt

object Constants 
    var REPEAT:Int = 0

在 ProductFragment.kt 中

if (Constants.REPEAT < 1)
            Constants.REPEAT = Constants.REPEAT + 1
            Handler(Looper.getMainLooper()).postDelayed(
                Toast.makeText(requireContext(),"got here", Toast.LENGTH_SHORT).show()
                val bottom = view.findNavController()
                bottom.navigate(R.id.action_product_Fragment_self)
            ,5000)
        

【讨论】：

将操作延迟 5000 毫秒根本不是解决方案。用 5001 毫秒读取数据怎么样？