RecyclerView 未显示在 Fragment 中

问题描述 投票：0回答：1

我正在尝试将 RecyclerView 添加到片段，但没有成功。我已经遵循了thisguide，但是其中RecyclerView被添加到MainActivity中，所以我尝试调整它。但是，我无法显示 RecyclerView。

我已经看过类似的问题，例如this one。

这是 RecyclerView 应该出现的 

fragment_add_recipe.xml
：

<?xml version="1.0" encoding="utf-8"?>
<androidx.core.widget.NestedScrollView 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:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".AddRecipeFragment">

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:padding="16dp">


        <com.google.android.material.textfield.TextInputLayout
            android:id="@+id/recipe_name_text_input_layout"
            style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:layout_constraintTop_toTopOf="parent">


            <com.google.android.material.textfield.TextInputEditText
                android:id="@+id/recipe_name_text_input"
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:inputType="text"
                android:hint="@string/recipe_name_hint"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintBottom_toBottomOf="parent"/>

        </com.google.android.material.textfield.TextInputLayout>


        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/ingredient_row_recycler_view"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            tools:itemCount="5"
            tools:listitem="@layout/ingredient_row_view"
            app:layout_constraintTop_toBottomOf="@id/recipe_name_text_input_layout"/>

        <Button
            android:id="@+id/save_recipe_button"
            android:layout_width="150sp"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_marginTop="20sp"
            android:text="Save"
            android:textColor="#ffffff"
            android:textSize="20sp"
            app:layout_constraintLeft_toLeftOf="parent"
            app:layout_constraintTop_toBottomOf="@id/ingredient_row_recycler_view"
            app:layout_constraintBottom_toBottomOf="parent"/>


    </androidx.constraintlayout.widget.ConstraintLayout>
</androidx.core.widget.NestedScrollView>


AddRecipeFragment.kt
：

package com.example.recipy

import CustomAdapter

import android.os.Bundle
import androidx.fragment.app.Fragment
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import android.widget.Toast
import androidx.databinding.DataBindingUtil
import androidx.recyclerview.widget.LinearLayoutManager
import com.example.recipy.databinding.FragmentAddRecipeBinding


class AddRecipeFragment : Fragment() {

    private var _binding: FragmentAddRecipeBinding? = null

//    For the ingredient row
    private val ingredientList : ArrayList<IngredientRowViewModel> = ArrayList()
    private lateinit var customAdapter : CustomAdapter

    private val binding get() = _binding!!

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

        // Inflate the Fragment layout
        _binding = FragmentAddRecipeBinding.inflate(inflater, container, false)

        setAdapter()

        return binding.root
    }

    private fun setAdapter(){
        customAdapter = CustomAdapter(ingredientList)
        binding.ingredientRowRecyclerView.apply {
            layoutManager = LinearLayoutManager(requireContext())
            adapter = customAdapter
        }
    }

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

        // Make button save the recipe in the SQL db
        binding.saveRecipeButton.setOnClickListener{
//            Some code for SQL connection here
        }

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


IngredientRowViewModel.kt
：

package com.example.recipy

data class IngredientRowViewModel(var ingredient: String) {

}


CustomAdapter.kt
：

import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.recyclerview.widget.RecyclerView
import com.example.recipy.IngredientRowViewModel
import com.example.recipy.R
import com.example.recipy.databinding.IngredientRowViewBinding

class CustomAdapter(private val ingredientList: ArrayList<IngredientRowViewModel>) : RecyclerView.Adapter<CustomAdapter.IngredientRowViewHolder>() {

    inner class IngredientRowViewHolder(private val binding : IngredientRowViewBinding) : RecyclerView.ViewHolder(binding.root) {
        fun bind(ingredient : IngredientRowViewModel){
            binding.ingredient = ingredient
        }
    }

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): IngredientRowViewHolder =
        IngredientRowViewHolder(IngredientRowViewBinding.inflate(LayoutInflater.from(parent.context), parent, false))


    override fun onBindViewHolder(holder: IngredientRowViewHolder, position: Int) {
        holder.bind(ingredientList[position])
    }

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

最后

ingredient_row_view.xml
：

<?xml version="1.0" encoding="utf-8"?>
<layout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">

    <data>
        <variable
            name="ingredient"
            type="com.example.recipy.IngredientRowViewModel" />
    </data>

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="horizontal"
        android:padding="5dp">

        <com.google.android.material.textfield.TextInputLayout
            android:id="@+id/ingredient_name_text_input_layout"
            style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            app:layout_constraintTop_toTopOf="parent">


            <com.google.android.material.textfield.TextInputEditText
                android:id="@+id/ingredient_name_text_input"
                android:layout_height="wrap_content"
                android:layout_width="match_parent"
                android:inputType="text"
                android:hint="@string/ingredient_name_hint"
                app:layout_constraintTop_toTopOf="parent"
                app:layout_constraintBottom_toBottomOf="parent"/>

        </com.google.android.material.textfield.TextInputLayout>

    </LinearLayout>

</layout>
android kotlin android-fragments android-recyclerview
1个回答
0
投票

我稍微更新了您的代码，正如我之前在评论中提到的，如果您想查看它，您必须向列表中添加一些项目。您可以添加按钮来添加项目，也可以使用固定大小的列表。

fragment_add_receipe.xml

添加新按钮，用于将成分添加到列表中。如果您不需要这个并且想要固定计数列表，只需创建包含空项目的列表，例如如下所示：

//This will show 5 empty text inputs in the recyclerView
private val ingredientList: ArrayList<IngredientRowViewModel> = arrayListOf(
    IngredientRowViewModel(""),
    IngredientRowViewModel(""),
    IngredientRowViewModel(""),
    IngredientRowViewModel(""),
    IngredientRowViewModel(""),
)

fragment_add_receipe.xml 带有新按钮：

<?xml version="1.0" encoding="utf-8"?>
<androidx.core.widget.NestedScrollView 
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:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".AddRecipeFragment">

<androidx.constraintlayout.widget.ConstraintLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:padding="16dp">


    <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/recipe_name_text_input_layout"
        
style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintTop_toTopOf="parent">


        <com.google.android.material.textfield.TextInputEditText
            android:id="@+id/recipe_name_text_input"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="Receipe name"
            android:inputType="text"
            app:layout_constraintBottom_toBottomOf="parent"
            app:layout_constraintTop_toTopOf="parent" />

    </com.google.android.material.textfield.TextInputLayout>


    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/ingredient_row_recycler_view"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        
app:layout_constraintTop_toBottomOf="@id/recipe_name_text_input_layout"
        tools:itemCount="5"
        tools:listitem="@layout/ingredient_row_view" />

    <!-- Add new button so you can add ingredients into your list -->
    <Button
        android:id="@+id/addIngredient"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="20sp"
        android:text="Add Ingredient"
        android:textColor="#ffffff"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        
app:layout_constraintTop_toBottomOf="@id/ingredient_row_recycler_view" />


    <Button
        android:id="@+id/save_recipe_button"
        android:layout_width="150sp"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_marginTop="20sp"
        android:text="Save"
        android:textColor="#ffffff"
        android:textSize="20sp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintTop_toBottomOf="@id/addIngredient" />


</androidx.constraintlayout.widget.ConstraintLayout>
</androidx.core.widget.NestedScrollView>

添加RecipeFragment.kt

将 

onClickListener
设置为 addIngredient 
Button
并在添加新成分时通知您的适配器。添加后，
RecyclerView
将显示一项（或多项），其中 
TextField
为空。

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


    binding.addIngredient.setOnClickListener {
        //add new ingredient with empty name into your list so your item will be shown
        ingredientList.add(IngredientRowViewModel(ingredient = ""))
        //Use notifyItemInserted instead of notifyDataSetChanged for better performance
        if (ingredientList.size == 0)
            customAdapter.notifyItemInserted(0)
        else
            customAdapter.notifyItemInserted(ingredientList.size - 1)
    }

    ...

}

ingredient_row_view.xml

这只是可选的，您有 

android:layout_height="match_parent"
，这意味着单个项目将占用大量空间，并且您必须滚动才能看到第二个项目，您应该将其更改为 
wrap_content
。

建议

  • 按照你提到的教程进行操作，一切都写在那里。
  • 检查 RecyclerView 的基础知识及其工作原理。我只是觉得你很难理解它。
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