即使指定了“match_parent”，使用 ConstraintLayout 的 RecyclerView 项目也不会填满屏幕的整个宽度
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【中文标题】即使指定了“match_parent”，使用 ConstraintLayout 的 RecyclerView 项目也不会填满屏幕的整个宽度【英文标题】：RecyclerView items using ConstraintLayout are not filling the entire width of the screen even though "match_parent" is specified 【发布时间】：2021-12-27 00:53:31 【问题描述】：我正在尝试设置回收站视图，使用 ConstraintLayout 显示元素。我用layout from this example by Google as a guideline.
然而，尽管一直指定android:layout_width="match_parent"，但最终显示在屏幕上的结果更类似于wrap_content。
到目前为止我所尝试的
-
将 ConstraintLayout 更改为 LinearLayout
*** question 中建议的解决方法
设置
android:layout_width=0，同时使用 ConstraintLayout 并将 start、end 和 top 锚定到父级
将整个内容封装在 CardView 中
在多个设备上运行应用程序，包括模拟和物理
相关代码
如果缺少其他感兴趣的内容，请告诉我。
recipe_list_entry.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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_
android:layout_ >
<TextView
android:id="@+id/recipe_title"
style="@style/Widget.RecipeTracker.ListItemTextView"
android:layout_marginHorizontal="@dimen/margin_between_elements"
android:background="@color/design_default_color_on_secondary"
android:layout_
android:fontFamily="sans-serif"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"
android:maxLines="1"
android:ellipsize="end"
tools:text="amazing stuff"/>
</androidx.constraintlayout.widget.ConstraintLayout>
styles.xml
<?xml version="1.0" encoding="utf-8"?>
<resources>
<style name="Widget.RecipeTracker.ListItemTextView" parent="Widget.MaterialComponents.TextView">
<item name="android:gravity">center_vertical</item>
<item name="android:layout_height">48dp</item>
<item name="android:textAppearance">?attr/textAppearanceBody1</item>
</style>
</resources>
recipe_list_fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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_
android:layout_
tools:context=".RecipeListFragment">
<androidx.recyclerview.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_
android:layout_
android:layout_marginHorizontal="@dimen/margin_between_elements"
android:scrollbars="vertical"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<com.google.android.material.floatingactionbutton.FloatingActionButton
android:id="@+id/add_entry"
android:layout_
android:layout_
android:layout_gravity="bottom|end"
android:layout_marginEnd="@dimen/add_entry_fab_margin"
android:layout_marginBottom="@dimen/add_entry_fab_margin"
android:contentDescription="@string/add_new_recipe_contentDescription"
app:layout_constraintBottom_toBottomOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:srcCompat="@drawable/ic_add" />
</androidx.constraintlayout.widget.ConstraintLayout>
RecipeListFragment.kt
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.fragment.app.Fragment
import androidx.fragment.app.activityViewModels
import androidx.navigation.fragment.findNavController
import androidx.recyclerview.widget.LinearLayoutManager
import me.lindenbauer.recipetracker.databinding.RecipeListFragmentBinding
/**
* A simple [Fragment] subclass as the default destination in the navigation.
*/
class RecipeListFragment : Fragment()
private val viewModel: RecipeTrackerViewModel by activityViewModels
RecipeTrackerViewModelFactory(
(activity?.application as RecipeTrackerApplication).database.recipeDao()
)
private var _binding: RecipeListFragmentBinding? = null
// This property is only valid between onCreateView and
// onDestroyView.
private val binding get() = _binding!!
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View?
_binding = RecipeListFragmentBinding.inflate(inflater, container, false)
return binding.root
override fun onViewCreated(view: View, savedInstanceState: Bundle?)
super.onViewCreated(view, savedInstanceState)
// Set up the automatic data updates for the recyclerView using the RecipeListAdapter
val adapter = RecipeListAdapter
// TODO: Define onRecipeClicked here
// This specifies how the "cards" are displayed by the recyclerView
binding.recyclerView.layoutManager = LinearLayoutManager(this.context)
binding.recyclerView.adapter = adapter
// Attach an observer on the allItems list to update the UI automatically when the data
// changes.
viewModel.allRecipes.observe(this.viewLifecycleOwner) recipes ->
recipes.let adapter.submitList(it)
binding.addEntry.setOnClickListener
findNavController().navigate(R.id.action_RecipeListFragment_to_AddEntryFragment)
override fun onDestroyView()
super.onDestroyView()
_binding = null
RecipeListAdapter.kt
import android.view.LayoutInflater
import android.view.ViewGroup
import androidx.recyclerview.widget.ListAdapter
import androidx.recyclerview.widget.DiffUtil
import androidx.recyclerview.widget.RecyclerView
import me.lindenbauer.recipetracker.data.Recipe
import me.lindenbauer.recipetracker.databinding.RecipeListEntryBinding
class RecipeListAdapter(private val onRecipeClicked: (Recipe) -> Unit):
ListAdapter<Recipe, RecipeListAdapter.RecipeViewHolder>(DiffCallback)
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecipeViewHolder
return RecipeViewHolder(
RecipeListEntryBinding.inflate(
LayoutInflater.from(
parent.context
)
)
)
override fun onBindViewHolder(holder: RecipeViewHolder, position: Int)
// Set up anything that is supposed to happen when interacting with a single item in the recyclerView
val current = getItem(position)
holder.itemView.setOnClickListener
onRecipeClicked(current)
holder.bind(current)
class RecipeViewHolder(private var binding: RecipeListEntryBinding) :
RecyclerView.ViewHolder(binding.root)
fun bind(recipe: Recipe)
binding.recipeTitle.text = recipe.recipeTitle
companion object
private val DiffCallback = object : DiffUtil.ItemCallback<Recipe>()
override fun areItemsTheSame(oldRecipe: Recipe, newRecipe: Recipe): Boolean
return oldRecipe === newRecipe
override fun areContentsTheSame(oldRecipe: Recipe, newRecipe: Recipe): Boolean
// TODO: Might need to make this more sophisticated
return oldRecipe.recipeTitle == newRecipe.recipeTitle
设计器预览
Android Studio 设计器预览
实际结果
在模拟 Pixel 5 上运行 API 30/Android 11 的实际结果
【问题讨论】：
【参考方案1】：你的代码在这里：
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecipeViewHolder
return RecipeViewHolder(
RecipeListEntryBinding.inflate(
LayoutInflater.from(
parent.context
)
)
)
不会在父视图的上下文中对视图进行膨胀，因此某些布局参数将不会像您期望的那样被处理。在这种情况下，如果它不知道它的父对象是谁，它的宽度就不能为match_parent。将其更改为：
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): RecipeViewHolder
return RecipeViewHolder(
RecipeListEntryBinding.inflate(
LayoutInflater.from(
parent.context
),
parent,
false
)
)
另外，一个小费。您不需要创建一个伴随对象来保存您的 DiffCallback。而且您也不需要拥有object 的属性。为了更简洁的代码，而不是
companion object
private val DiffCallback = object : DiffUtil.ItemCallback<Recipe>()
//...
你可以放
private object DiffCallback: DiffUtil.ItemCallback<Recipe>()
//...
【讨论】：
谢谢，这似乎成功了。只是为了我的理解，因为我现在正在学习原生 Android：The problem was this usecase correct? 你能否指出我记录了 Binding 类生成的方法的地方？我在此评论中链接的 Android 文档中甚至没有链接该方法。我找不到任何记录 ViewBinding.inflate() 可用覆盖的内容。它可能会帮助我更多地理解 ViewBinding。 我还没有找到任何方法来查看绑定方法的特定文档，但是ViewBinding.inflate 的两个重载与 LayoutInflater.inflate 的重载匹配，除了视图 ID 的第一个参数是换成了 LayoutInflater 本身。还有ViewBinding.bind() 为已经膨胀的视图创建绑定实例。这对于您将布局 ID 传递给超级构造函数的片段特别有用。您可以省略整个 onCreateView 样板文件并将您的绑定绑定到 onViewCreated 中。以上是关于即使指定了“match_parent”，使用 ConstraintLayout 的 RecyclerView 项目也不会填满屏幕的整个宽度的主要内容，如果未能解决你的问题，请参考以下文章