Kotlin应用程序在按钮按下后崩溃，出现NullPointerException。

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英文:

Kotlin app crashes after button press with NullPointerException

问题

I am making a Kotlin app in Android Studio where I can add foods with their calorie values like a list.

How it is supposed to work is that the two EditText components, "etName" and "etCalories," would be passed into a list, then the TextView inside the RecyclerView should show them.

The issue is, if I press the button to add the item, the app crashes.

Here's the logcat

  1. FATAL EXCEPTION: main
  2.     Process: com.example.bbar, PID: 25930
  3.     java.lang.NullPointerException
  4.         at com.example.bbar.ui.home.FoodlistadapterKt.getBinding(foodlistadapter.kt:16)
  5.         at com.example.bbar.ui.home.FoodlistadapterKt.access$getBinding(foodlistadapter.kt:1)
  6.         at com.example.bbar.ui.home.Foodlistadapter.onBindViewHolder(foodlistadapter.kt:57)
  7.         at com.example.bbar.ui.home.Foodlistadapter.onBindViewHolder(foodlistadapter.kt:18)

Here's the code

foodlistadapter.kt

  1. package com.example.bbar.ui.home
  3. import android.annotation.SuppressLint
  4. import android.view.LayoutInflater
  5. import android.view.View
  6. import android.view.ViewGroup
  7. import androidx.recyclerview.widget.RecyclerView
  8. import com.example.bbar.R
  9. import android.graphics.Paint.STRIKE_THRU_TEXT_FLAG
  10. import android.widget.TextView
  11. import com.example.bbar.databinding.FooditemBinding
  13. @SuppressLint("StaticFieldLeak")
  14. private var _binding: FooditemBinding? = null
  15. private val binding get() =  _binding!!
  17. class Foodlistadapter(
  18.     private val foods: MutableList<food>
  19. ) : RecyclerView.Adapter<Foodlistadapter.foodlistviewholder>() {
  21.     class foodlistviewholder(itemView: View) : RecyclerView.ViewHolder(itemView)
  23.     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): foodlistviewholder {
  24.         return foodlistviewholder(
  25.             LayoutInflater.from(parent.context).inflate(
  26.                 R.layout.fragment_home,
  27.                 parent,
  28.                 false
  29.             )
  30.         )
  31.     }
  33.     fun addFood(food: food) {
  34.         foods.add(food)
  35.         notifyItemInserted(foods.size - 1)
  36.     }
  38.     fun deleteFood() {
  39.         foods.removeAll { foods -> foods.isChecked }
  40.         notifyDataSetChanged()
  41.     }
  43.     private fun toggleStrikeThrough(tvFood: TextView, isChecked: Boolean) {
  44.         if (isChecked) {
  45.             tvFood.paintFlags = tvFood.paintFlags or STRIKE_THRU_TEXT_FLAG
  46.         } else {
  47.             tvFood.paintFlags = tvFood.paintFlags or STRIKE_THRU_TEXT_FLAG.inv()
  48.         }
  49.     }
  51.     override fun onBindViewHolder(holder: foodlistviewholder, position: Int) {
  52.         val currentFood = foods[position]
  53.         holder.itemView.apply {
  54.             binding.tvFood.text = currentFood.name
  55.             binding.tvCalories.text = currentFood.calories.toString()
  56.             binding.cbDelete.isChecked = currentFood.isChecked
  57.             toggleStrikeThrough(binding.tvFood, currentFood.isChecked)
  58.             binding.cbDelete.setOnCheckedChangeListener { _, isChecked ->
  59.                 toggleStrikeThrough(binding.tvFood, isChecked)
  60.                 currentFood.isChecked = !currentFood.isChecked
  61.             }
  62.         }
  63.     }
  65.     override fun getItemCount(): Int {
  66.         return foods.size
  67.     }
  68. }

FragmentHome.kt

  1. package com.example.bbar.ui.home
  3. import android.os.Bundle
  4. import android.view.LayoutInflater
  5. import android.view.View
  6. import android.view.ViewGroup
  7. import androidx.fragment.app.Fragment
  8. import androidx.recyclerview.widget.LinearLayoutManager
  9. import com.example.bbar.R
  10. import com.example.bbar.databinding.FragmentHomeBinding
  12. class HomeFragment : Fragment() {
  14.     private var _binding: FragmentHomeBinding? = null
  15.     private val binding get() = _binding!!
  17.     private lateinit var foodlistadapter: Foodlistadapter
  19.     override fun onCreateView(
  20.         inflater: LayoutInflater, container: ViewGroup?,
  21.         savedInstanceState: Bundle?
  22.     ): View {
  23.         _binding = FragmentHomeBinding.inflate(inflater, container, false)
  24.         return binding.root
  25.     }
  27.     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
  28.         super.onViewCreated(view, savedInstanceState)
  30.         foodlistadapter = Foodlistadapter(mutableListOf())
  31.         binding.rvFoodItems.adapter = foodlistadapter
  32.         binding.rvFoodItems.layoutManager = LinearLayoutManager(activity)
  34.         binding.bSubmit.setOnClickListener {
  35.             val foodTitle = binding.etName.text.toString()
  36.             val foodCalories = binding.etCalories.text.toString()
  37.             if (foodTitle.isNotEmpty()) {
  38.                 val food = food(foodTitle, foodCalories.toInt(), false)
  39.                 foodlistadapter.addFood(food)
  40.                 binding.etName.text.clear()
  41.                 binding.etCalories.text.clear()
  42.             }
  43.         }
  44.         binding.bDelete.setOnClickListener {
  45.             foodlistadapter.deleteFood()
  46.         }
  47.     }
  49.     override fun onDestroy() {
  50.         super.onDestroy()
  51.         _binding = null
  52.     }
  53. }

Summary: Tried to add food with its respected calorie value with a button, but the program crashes.

英文:

I am making a Kotlin app in Android Studio where I can add foods with their calorie values like a list.

How it is supposed to work is that the two EditText components, "etName" and "etCalories", would be passed into a list, then the TextView inside the RecyclerView should show them.

The issue is, if I press the button to add the item, the app crashes.

Here's the logcat

  1. FATAL EXCEPTION: main
  2.     Process: com.example.bbar, PID: 25930
  3.     java.lang.NullPointerException
  4.         at com.example.bbar.ui.home.FoodlistadapterKt.getBinding(foodlistadapter.kt:16)
  5.         at com.example.bbar.ui.home.FoodlistadapterKt.access$getBinding(foodlistadapter.kt:1)
  6.         at com.example.bbar.ui.home.Foodlistadapter.onBindViewHolder(foodlistadapter.kt:57)
  7.         at com.example.bbar.ui.home.Foodlistadapter.onBindViewHolder(foodlistadapter.kt:18)

Here's the code

foodlistadapter.kt

  1. package com.example.bbar.ui.home
  3. import android.annotation.SuppressLint
  4. import android.view.LayoutInflater
  5. import android.view.View
  6. import android.view.ViewGroup
  7. import androidx.recyclerview.widget.RecyclerView
  8. import com.example.bbar.R
  9. import android.graphics.Paint.STRIKE_THRU_TEXT_FLAG
  10. import android.widget.TextView
  11. import com.example.bbar.databinding.FooditemBinding
  14. @SuppressLint(&quot;StaticFieldLeak&quot;)
  15. private var _binding: FooditemBinding? = null
  16. private val binding get() =  _binding!!
  18. class Foodlistadapter(
  20.     private val foods: MutableList&lt;food&gt;
  21. ) : RecyclerView.Adapter&lt;Foodlistadapter.foodlistviewholder&gt;() {
  23.     class foodlistviewholder(itemView: View) : RecyclerView.ViewHolder(itemView)
  25.     override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): foodlistviewholder {
  26.         return foodlistviewholder(
  27.             LayoutInflater.from(parent.context).inflate(
  28.                 R.layout.fragment_home,
  29.                 parent,
  30.                 false
  31.             )
  32.         )
  33.     }
  35.      fun addFood(food: food) {
  36.         foods.add(food)
  37.         notifyItemInserted(foods.size - 1)
  38.     }
  40.      fun deleteFood() {
  41.         foods.removeAll { foods -&gt; foods.isChecked }
  42.         notifyDataSetChanged()
  44.     }
  46.     private fun toggleStrikeThrough(tvFood: TextView, isChecked: Boolean) {
  47.         if (isChecked) {
  48.             tvFood.paintFlags = tvFood.paintFlags or STRIKE_THRU_TEXT_FLAG
  49.         } else {
  50.             tvFood.paintFlags = tvFood.paintFlags or STRIKE_THRU_TEXT_FLAG.inv()
  51.         }
  52.     }
  54.     override fun onBindViewHolder(holder: foodlistviewholder, position: Int) {
  55.         val currentFood = foods[position]
  56.         holder.itemView.apply {
  57.             binding.tvFood.text = currentFood.name
  58.             binding.tvCalories.text= currentFood.calories.toString()
  59.             binding.cbDelete.isChecked = currentFood.isChecked
  60.             toggleStrikeThrough(binding.tvFood, currentFood.isChecked)
  61.             binding.cbDelete.setOnCheckedChangeListener { _, isChecked -&gt;
  62.                 toggleStrikeThrough(binding.tvFood, isChecked)
  63.                 currentFood.isChecked = !currentFood.isChecked
  64.             }
  65.         }
  66.     }
  68.     override fun getItemCount(): Int {
  69.         return foods.size
  70.     }
  71. }
  1. package com.example.bbar.ui.home
  3. import android.os.Bundle
  4. import android.view.LayoutInflater
  5. import android.view.View
  6. import android.view.ViewGroup
  7. import androidx.fragment.app.Fragment
  8. import androidx.recyclerview.widget.LinearLayoutManager
  9. import com.example.bbar.R
  11. import com.example.bbar.databinding.FragmentHomeBinding
  15. class HomeFragment : Fragment() {
  17.     private var _binding: FragmentHomeBinding? = null
  18.     private val binding get() = _binding!!
  20.     private lateinit var foodlistadapter: Foodlistadapter
  22.     override fun onCreateView(
  23.         inflater: LayoutInflater, container: ViewGroup?,
  24.         savedInstanceState: Bundle?
  25.     ): View {
  26.         _binding = FragmentHomeBinding.inflate(inflater, container, false)
  28.         return binding!!.root
  29.     }
  31.     override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
  32.         super.onViewCreated(view, savedInstanceState)
  34.         foodlistadapter = Foodlistadapter(mutableListOf())
  35.         binding.rvFoodItems.adapter = foodlistadapter
  36.         binding.rvFoodItems.layoutManager = LinearLayoutManager(activity)
  38.         binding.bSubmit.setOnClickListener{
  39.             val foodTitle= binding.etName.text.toString()
  40.             val foodCalories = binding.etCalories.text.toString()
  41.             if (foodTitle.isNotEmpty()){
  42.                 val food= food(foodTitle, foodCalories.toInt(), false )
  43.                 foodlistadapter.addFood(food)
  44.                 binding.etName.text.clear()
  45.                 binding.etCalories.text.clear()
  46.             }
  47.         }
  48.         binding.bDelete.setOnClickListener{
  49.             foodlistadapter.deleteFood()
  50.         }
  51.     }
  53.     override fun onDestroy() {
  54.         super.onDestroy()
  55.         _binding = null
  56.     }
  57. }

Summary: Tried to add food with its respected calorie value with a button, but program crashes.

答案1

得分: 0

你的 binding 为空，而且没有被正确使用。

首先，将声明移到类外部，即：

  1. @SuppressLint("StaticFieldLeak")
  2. private var _binding: FooditemBinding? = null
  3. private val binding get() = _binding!!

将你的 ViewHolder 实现更改为：

  1. class FoodListViewHolder(val binding: FooditemBinding) : RecyclerView.ViewHolder(binding.root)

在 onCreateViewHolder 中实例化该绑定：

  1. override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FoodListViewHolder {
  2.     val inflater = LayoutInflater.from(parent.context)
  3.     return FoodListViewHolder(FooditemBinding.inflate(inflater, parent, false))
  4. }

在 onBindViewHolder 中使用绑定：

  1. override fun onBindViewHolder(holder: FoodListViewHolder, position: Int) {
  2.     val currentFood = foods[position]
  4.     holder.binding.apply {
  5.         tvFood.text = currentFood.name
  6.         tvCalories.text = currentFood.calories.toString()
  7.         cbDelete.isChecked = currentFood.isChecked
  8.         toggleStrikeThrough(tvFood, isChecked)
  9.         cbDelete.setOnCheckedChangeListener { _, isChecked ->
  10.             toggleStrikeThrough(tvFood, isChecked)
  11.             currentFood.isChecked = !currentFood.isChecked
  12.         }
  13.     }
  14. }
英文:

You binding is null & also it isn't used correctly.
First of, remove the declaration outside the class i.e:

  1. @SuppressLint(&quot;StaticFieldLeak&quot;)
  2. private var _binding: FooditemBinding? = null
  3. private val binding get() =  _binding!!

Change your ViewHolder implementation to:

  1. class FoodListViewHolder(val binding: FooditemBinding) : RecyclerView.ViewHolder(binding.root)

Inflate that binding in onCreateViewHolder:

  1. override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): FoodListViewHolder {
  2.     val inflater = LayoutInflater.from(parent.context)
  3.     return FoodListViewHolder(FooditemBinding.inflate(inflater, parent, false))
  4. }

Use the binding in onBindViewHolder:

  1. override fun onBindViewHolder(holder: FoodListViewHolder, position: Int) {
  2.     val currentFood = foods[position]
  4.     holder.binding.apply {
  5.         tvFood.text = currentFood.name
  6.         tvCalories.text= currentFood.calories.toString()
  7.         cbDelete.isChecked = currentFood.isChecked
  8.         toggleStrikeThrough(tvFood, isChecked)
  9.         cbDelete.setOnCheckedChangeListener { _, isChecked -&gt;
  10.             toggleStrikeThrough(tvFood, isChecked)
  11.             currentFood.isChecked = !currentFood.isChecked
  12.         }
  13.     }
  14. }

huangapple
  • 本文由 发表于 2023年6月19日 00:01:05
  • 转载请务必保留本文链接：https://go.coder-hub.com/76501415.html
  • android
  • button
  • fragment
  • kotlin
  • nullpointerexception
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