如何在 RecyclerView.ListAdapter 中查看我的列表？
How can I see my List in my RecyclerView.ListAdapter?
所以我正在做一个项目，我想看看我的 RecyclerView 是否有效。这是我目前得到的
数据class:
@Parcelize
@Entity(tableName = "asteroid_feed")
data class Asteroid(val id: Long, val codename: String, val closeApproachDate: String,
val absoluteMagnitude: Double, val estimatedDiameter: Double,
val relativeVelocity: Double, val distanceFromEarth: Double,
val isPotentiallyHazardous: Boolean) : Parcelable
适配器
class AsteroidViewAdapter (private val list: MutableList<Asteroid>) : ListAdapter<Asteroid, AsteroidViewAdapter.AsteroidViewHolder>(DiffCallback) {
companion object DiffCallback : DiffUtil.ItemCallback<Asteroid>() {
override fun areItemsTheSame(oldItem: Asteroid, newItem: Asteroid): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: Asteroid, newItem: Asteroid): Boolean {
return oldItem == newItem
}
}
override fun onCreateViewHolder(
parent: ViewGroup,
viewType: Int
): AsteroidViewHolder {
return AsteroidViewHolder(AsteroidListContainerBinding.inflate(LayoutInflater.from(parent.context)))
}
override fun onBindViewHolder(holder: AsteroidViewHolder, position: Int) {
holder.bind(getItem(position))
}
class AsteroidViewHolder (private val binding: AsteroidListContainerBinding) : RecyclerView.ViewHolder(binding.root) {
fun bind(item: Asteroid){
binding.value = item
}
}
}
碎片
class MainFragment : Fragment() {
private lateinit var manager: RecyclerView.LayoutManager
private val viewModel: MainViewModel by lazy {
ViewModelProvider(this).get(MainViewModel::class.java)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
val binding = FragmentMainBinding.inflate(inflater)
binding.lifecycleOwner = this
binding.viewModel = viewModel
val mutableList: MutableList<Asteroid> = ArrayList()
mutableList.add(Asteroid(1, "fgnuugrhrg", "bihagtyjerwailgubivb", 4.0, 8.0,3.0, 9.0, false))
mutableList.add(Asteroid(2, "fguk.nuugrhrg", "bidjswjyhagrwailgubivb", 3.0, 90.0,355.0, 9.0, true))
mutableList.add(Asteroid(3, "fgnssuugrhrg", "bshjtihagrwailgubivb", 4.0, 33.0,33.0, 9.0, false))
mutableList.add(Asteroid(4, "fgnuw4suugrhrg", "bjsryjihagrwailgubivb", 6.0, 8.0,11.0, 9.0, true))
mutableList.add(Asteroid(5, "fgnuugrudkdkhrg", "bihjjkkuagrwailgubivb", 4.0, 5.0,77.0, 9.0, false))
manager = LinearLayoutManager(this.context)
binding.asteroidRecycler.apply {
adapter = AsteroidViewAdapter(mutableList)
layoutManager = manager
}
setHasOptionsMenu(true)
return binding.root
}
override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
inflater.inflate(R.menu.main_overflow_menu, menu)
super.onCreateOptionsMenu(menu, inflater)
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
return true
}
}
XML 文件：
布局
<?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="viewModel"
type="com.udacity.asteroidradar.main.MainViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/app_background">
<FrameLayout
android:id="@+id/activity_main_image_of_the_day_layout"
android:layout_width="match_parent"
android:layout_height="220dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<ImageView
android:id="@+id/activity_main_image_of_the_day"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:adjustViewBounds="true"
android:scaleType="centerCrop"
app:srcCompat="@drawable/placeholder_picture_of_day"/>
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="16dp"
android:textColor="@android:color/white"
android:textStyle="bold"
android:textSize="20sp"
android:layout_gravity="bottom"
android:background="#55010613"
android:text="@string/image_of_the_day" />
</FrameLayout>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/asteroid_recycler"
android:layout_width="0dp"
android:layout_height="0dp"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/activity_main_image_of_the_day_layout"
app:layout_constraintVertical_bias="0.0" />
<ProgressBar
android:id="@+id/status_loading_wheel"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:indeterminate="true"
android:visibility="gone"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
容器：
<?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"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="value"
type="com.udacity.asteroidradar.Asteroid" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/app_background">
<TextView
android:id="@+id/codename"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:textColor="@color/default_text_color"
android:textSize="20sp"
android:textStyle="bold"
android:text="@{value.codename}"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="@string/codename" />
<TextView
android:id="@+id/date_field"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="16dp"
android:textColor="@color/default_text_color"
android:text="@{value.closeApproachDate}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="@+id/codename"
app:layout_constraintTop_toBottomOf="@+id/codename"
tools:text="@tools:sample/date/mmddyy" />
<ImageView
android:id="@+id/danger_pic"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="16dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toEndOf="@+id/codename"
app:layout_constraintTop_toTopOf="parent"
tools:srcCompat="@drawable/ic_status_potentially_hazardous" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
如您所见，我使用 MutableList 填充字段并在 fragment_main 中的 RecyclerView.ListAdapter 上查看该列表，但它没有显示任何内容。同样，这只是检查 RecyclerView 是否正常工作。感谢您的帮助。
您将列表发送到适配器但未使用 submitList()
提交的问题
您可以在适配器的 init{} 中执行此操作
class AsteroidViewAdapter(private val list: MutableList<Asteroid>) :
ListAdapter<Asteroid, AsteroidViewAdapter.AsteroidViewHolder>(DiffCallback) {
init {
submitList(list)
}
// omitted code
根据我的理解，列表视图不知道要填充列表中项目的大小。因此，您需要通过下面的内部列表适配器 class.
覆盖项目列表计数
override fun getItemCount(): Int {
return items.size
}
所以我正在做一个项目，我想看看我的 RecyclerView 是否有效。这是我目前得到的
数据class:
@Parcelize
@Entity(tableName = "asteroid_feed")
data class Asteroid(val id: Long, val codename: String, val closeApproachDate: String,
val absoluteMagnitude: Double, val estimatedDiameter: Double,
val relativeVelocity: Double, val distanceFromEarth: Double,
val isPotentiallyHazardous: Boolean) : Parcelable
适配器
class AsteroidViewAdapter (private val list: MutableList<Asteroid>) : ListAdapter<Asteroid, AsteroidViewAdapter.AsteroidViewHolder>(DiffCallback) {
companion object DiffCallback : DiffUtil.ItemCallback<Asteroid>() {
override fun areItemsTheSame(oldItem: Asteroid, newItem: Asteroid): Boolean {
return oldItem.id == newItem.id
}
override fun areContentsTheSame(oldItem: Asteroid, newItem: Asteroid): Boolean {
return oldItem == newItem
}
}
override fun onCreateViewHolder(
parent: ViewGroup,
viewType: Int
): AsteroidViewHolder {
return AsteroidViewHolder(AsteroidListContainerBinding.inflate(LayoutInflater.from(parent.context)))
}
override fun onBindViewHolder(holder: AsteroidViewHolder, position: Int) {
holder.bind(getItem(position))
}
class AsteroidViewHolder (private val binding: AsteroidListContainerBinding) : RecyclerView.ViewHolder(binding.root) {
fun bind(item: Asteroid){
binding.value = item
}
}
}
碎片
class MainFragment : Fragment() {
private lateinit var manager: RecyclerView.LayoutManager
private val viewModel: MainViewModel by lazy {
ViewModelProvider(this).get(MainViewModel::class.java)
}
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
val binding = FragmentMainBinding.inflate(inflater)
binding.lifecycleOwner = this
binding.viewModel = viewModel
val mutableList: MutableList<Asteroid> = ArrayList()
mutableList.add(Asteroid(1, "fgnuugrhrg", "bihagtyjerwailgubivb", 4.0, 8.0,3.0, 9.0, false))
mutableList.add(Asteroid(2, "fguk.nuugrhrg", "bidjswjyhagrwailgubivb", 3.0, 90.0,355.0, 9.0, true))
mutableList.add(Asteroid(3, "fgnssuugrhrg", "bshjtihagrwailgubivb", 4.0, 33.0,33.0, 9.0, false))
mutableList.add(Asteroid(4, "fgnuw4suugrhrg", "bjsryjihagrwailgubivb", 6.0, 8.0,11.0, 9.0, true))
mutableList.add(Asteroid(5, "fgnuugrudkdkhrg", "bihjjkkuagrwailgubivb", 4.0, 5.0,77.0, 9.0, false))
manager = LinearLayoutManager(this.context)
binding.asteroidRecycler.apply {
adapter = AsteroidViewAdapter(mutableList)
layoutManager = manager
}
setHasOptionsMenu(true)
return binding.root
}
override fun onCreateOptionsMenu(menu: Menu, inflater: MenuInflater) {
inflater.inflate(R.menu.main_overflow_menu, menu)
super.onCreateOptionsMenu(menu, inflater)
}
override fun onOptionsItemSelected(item: MenuItem): Boolean {
return true
}
}
XML 文件： 布局
<?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="viewModel"
type="com.udacity.asteroidradar.main.MainViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@color/app_background">
<FrameLayout
android:id="@+id/activity_main_image_of_the_day_layout"
android:layout_width="match_parent"
android:layout_height="220dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent">
<ImageView
android:id="@+id/activity_main_image_of_the_day"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:adjustViewBounds="true"
android:scaleType="centerCrop"
app:srcCompat="@drawable/placeholder_picture_of_day"/>
<TextView
android:id="@+id/textView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="16dp"
android:textColor="@android:color/white"
android:textStyle="bold"
android:textSize="20sp"
android:layout_gravity="bottom"
android:background="#55010613"
android:text="@string/image_of_the_day" />
</FrameLayout>
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/asteroid_recycler"
android:layout_width="0dp"
android:layout_height="0dp"
app:layoutManager="androidx.recyclerview.widget.LinearLayoutManager"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/activity_main_image_of_the_day_layout"
app:layout_constraintVertical_bias="0.0" />
<ProgressBar
android:id="@+id/status_loading_wheel"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:indeterminate="true"
android:visibility="gone"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintLeft_toLeftOf="parent"
app:layout_constraintRight_toRightOf="parent"
app:layout_constraintTop_toTopOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
容器：
<?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"
xmlns:tools="http://schemas.android.com/tools">
<data>
<variable
name="value"
type="com.udacity.asteroidradar.Asteroid" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:background="@color/app_background">
<TextView
android:id="@+id/codename"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginStart="16dp"
android:layout_marginTop="16dp"
android:textColor="@color/default_text_color"
android:textSize="20sp"
android:textStyle="bold"
android:text="@{value.codename}"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent"
tools:text="@string/codename" />
<TextView
android:id="@+id/date_field"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginBottom="16dp"
android:textColor="@color/default_text_color"
android:text="@{value.closeApproachDate}"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintStart_toStartOf="@+id/codename"
app:layout_constraintTop_toBottomOf="@+id/codename"
tools:text="@tools:sample/date/mmddyy" />
<ImageView
android:id="@+id/danger_pic"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="24dp"
android:layout_marginEnd="16dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="1.0"
app:layout_constraintStart_toEndOf="@+id/codename"
app:layout_constraintTop_toTopOf="parent"
tools:srcCompat="@drawable/ic_status_potentially_hazardous" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
如您所见，我使用 MutableList 填充字段并在 fragment_main 中的 RecyclerView.ListAdapter 上查看该列表，但它没有显示任何内容。同样，这只是检查 RecyclerView 是否正常工作。感谢您的帮助。
您将列表发送到适配器但未使用 submitList()
您可以在适配器的 init{} 中执行此操作
class AsteroidViewAdapter(private val list: MutableList<Asteroid>) :
ListAdapter<Asteroid, AsteroidViewAdapter.AsteroidViewHolder>(DiffCallback) {
init {
submitList(list)
}
// omitted code
根据我的理解，列表视图不知道要填充列表中项目的大小。因此，您需要通过下面的内部列表适配器 class.
覆盖项目列表计数 override fun getItemCount(): Int {
return items.size
}