那些遇到过的问题

Recycler View 中的约束集动画动画不正确

Var*_* I. 7 animation android android-constraintlayout constraintset

我正在为我的回收站视图项目使用约束布局。为了动画（展开/折叠）它们，我使用约束集动画。开场动画在所有项目上运行良好。关闭动画也运行良好，但是当关闭动画在不是最后一个的项目上开始时，所有项目在动画开始时都会跳起来，而不是在动画结束时。

动画在项目点击时执行：

itemView.setOnClickListener {
                val smallItemConstraint = ConstraintSet()
                smallItemConstraint.clone(itemView.context, R.layout.day_of_week_small)
                val largeItemConstraint = ConstraintSet()
                largeItemConstraint.clone(itemView.context, R.layout.day_of_week)

                val constraintToApply = if (isViewExpanded) smallItemConstraint else
                    largeItemConstraint

                animateItemView(constraintToApply, itemView.dayOfWeekConstraintLayout)

                if (!isViewExpanded) {
                    itemView.dayOfWeekWeatherIcon.visibility = View.VISIBLE
                } else {
                    itemView.dayOfWeekWeatherIcon.visibility = View.GONE
                }

                isViewExpanded = !isViewExpanded
            }
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animateItemView 在哪里：

private fun animateItemView(constraintToApply: ConstraintSet,
                                constraintLayout: ConstraintLayout) {
        TransitionManager.beginDelayedTransition(constraintLayout)
        constraintToApply.applyTo(constraintLayout)
    }
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day_of_week.xml（扩展）布局：

<?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:id="@+id/dayOfWeekConstraintLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <ImageView
        android:id="@+id/dayOfWeekWeatherIcon"
        android:layout_width="90dp"
        android:layout_height="90dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:contentDescription="@string/weather_image"
        app:layout_constraintBottom_toBottomOf="@+id/dayOfWeekHumidityLabel"
        app:layout_constraintEnd_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:srcCompat="@tools:sample/avatars" />

    <TextView
        android:id="@+id/dayOfWeekText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/today"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/dayOfWeekItemVerticalGuideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_begin="192dp" />

    <TextView
        android:id="@+id/dayOfWeekCurrentTemperatureText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textAllCaps="true"
        android:textSize="24sp"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekText" />

    <TextView
        android:id="@+id/dayOfWeekDegreeCelsiusSign"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/degree_celsius"
        android:textAllCaps="true"
        android:textSize="24sp"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekCurrentTemperatureText"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekText" />

    <TextView
        android:id="@+id/dayOfWeekWeatherStateText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/weather_state_text"
        android:textSize="24sp"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekDegreeCelsiusSign" />

    <TextView
        android:id="@+id/dayOfWeekWindLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/wind_label"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekHumidityLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="8dp"
        android:text="@string/humidityLabel"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWindLabel" />

    <TextView
        android:id="@+id/dayOfWeekWindDirection"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekWindLabel"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekWindSpeed"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textSize="14sp"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekWindDirection"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekWindSpeedLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/wind_speed"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekWindSpeed"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekHumidityText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekHumidityLabel"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWindSpeedLabel" />

    <TextView
        android:id="@+id/dayOfWeekHumidityPercentageLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="8dp"
        android:text="@string/percentage_sign"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekHumidityText"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWindSpeedLabel" />

</androidx.constraintlayout.widget.ConstraintLayout>
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和 day_of_week_small.xml（折叠）布局：

<?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:id="@+id/dayOfWeekConstraintLayout"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <ImageView
        android:id="@+id/dayOfWeekWeatherIcon"
        android:layout_width="90dp"
        android:layout_height="90dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginBottom="8dp"
        android:contentDescription="@string/weather_image"
        android:visibility="gone"
        app:layout_constraintBottom_toBottomOf="@+id/dayOfWeekHumidityLabel"
        app:layout_constraintEnd_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        tools:srcCompat="@tools:sample/avatars" />

    <TextView
        android:id="@+id/dayOfWeekText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/today"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.constraintlayout.widget.Guideline
        android:id="@+id/dayOfWeekItemVerticalGuideline"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        app:layout_constraintGuide_begin="192dp" />

    <TextView
        android:id="@+id/dayOfWeekCurrentTemperatureText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textAllCaps="true"
        android:textSize="40sp"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekText" />

    <TextView
        android:id="@+id/dayOfWeekDegreeCelsiusSign"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/degree_celsius"
        android:textAllCaps="true"
        android:textSize="40sp"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekCurrentTemperatureText"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekText" />

    <TextView
        android:id="@+id/dayOfWeekWeatherStateText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/weather_state_text"
        android:textSize="24sp"
        android:visibility="gone"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekDegreeCelsiusSign" />

    <TextView
        android:id="@+id/dayOfWeekWindLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/wind_label"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        android:visibility="gone"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekHumidityLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="8dp"
        android:text="@string/humidityLabel"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        android:visibility="gone"
        app:layout_constraintStart_toStartOf="@+id/dayOfWeekItemVerticalGuideline"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWindLabel" />

    <TextView
        android:id="@+id/dayOfWeekWindDirection"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        android:visibility="gone"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekWindLabel"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekWindSpeed"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textSize="14sp"
        android:visibility="gone"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekWindDirection"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekWindSpeedLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:text="@string/wind_speed"
        android:textSize="14sp"
        android:textStyle="bold"
        android:visibility="gone"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekWindSpeed"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWeatherStateText" />

    <TextView
        android:id="@+id/dayOfWeekHumidityText"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="8dp"
        android:layout_marginTop="8dp"
        android:textSize="14sp"
        android:textStyle="bold"
        android:visibility="gone"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekHumidityLabel"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekWindSpeedLabel" />

    <TextView
        android:id="@+id/dayOfWeekHumidityPercentageLabel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="8dp"
        android:text="@string/percentage_sign"
        android:textAllCaps="true"
        android:textSize="14sp"
        android:textStyle="bold"
        android:visibility="gone"
        app:layout_constraintStart_toEndOf="@+id/dayOfWeekCurrentTemperatureText"
        app:layout_constraintTop_toBottomOf="@+id/dayOfWeekCurrentTemperatureText" />

</androidx.constraintlayout.widget.ConstraintLayout>
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这里有什么问题，我该如何解决？谢谢你。

动画示例：

https://gph.is/g/aj8GdB4

idu*_*olz 2

在我们了解如何让一切正常工作之前，让我们先看看是什么导致了 gif 中的行为。

\n

其他项目视图跳跃的原因是因为动画纯粹是视觉的。也就是说，折叠动画实际上并不从布局角度对项目的高度进行动画处理，它仅对项目的绘制方式进行动画处理。这样做是出于性能原因（想象一下必须每秒重新布局所有视图 60 次）。这就是为什么当您的项目折叠时，所有其他视图都会跳转到最终布局位置。

\n

RecyclerView 非常擅长为其子级的高度设置动画，这就是我们将用来解决整个动画问题的方法。我在下面概述了完整的解决方案。

\n
\n

预览 GIF：https://giphy.com/gifs/SVlBnpeW3wIwNIVpVU

\n

经过一些实验，我能够让 ConstraintLayout + ConstrainSet + RecyclerViews 工作。我将分享我是如何让它发挥作用的。

\n

代码

\n

这是代码的快速预览。

\n
private inner class MatchInfoAdapter (\n  private val context: Context\n) : RecyclerView.Adapter<RecyclerView.ViewHolder>() {\n\n  private var items = listOf<MatchItem>()\n  private val inflater: LayoutInflater = LayoutInflater.from(context)\n\n  override fun onCreateViewHolder(\n    parent: ViewGroup, \n    viewType: Int\n  ): RecyclerView.ViewHolder = \n    FullViewHolder(inflater.inflate(viewType, parent, false))\n\n  override fun onBindViewHolder(\n    holder: RecyclerView.ViewHolder,\n    position: Int,\n    payloads: MutableList<Any>\n  ) {\n    if (payloads.isEmpty()) {\n      super.onBindViewHolder(holder, position, payloads)\n    } else {\n      val item = items[position]\n      val h = holder as FullViewHolder\n  \n      if (!item.isExpanded) {\n        h.collapsedConstraintSet.applyTo(h.rootView)\n      }\n    }\n  }\n\n  override fun onBindViewHolder(holder: RecyclerView.ViewHolder, position: Int) {\n    val item = items[position]\n    val h = holder as FullViewHolder\n    val isExpanded = item.isExpanded\n  \n    val constraint = if (isExpanded) \n      h.expandedConstraintSet \n    else \n      h.collapsedConstraintSet\n    constraint.applyTo(h.rootView)\n\n    bindGeneralViews(h, item, isExpanded)\n    if (isExpanded) {\n      bindExpandedExtraViews(h, item)\n    }\n\n    h.clickView.setOnClickListener {\n      toggleExpanded(h)\n    }\n  }\n\n\n  private fun bindGeneralViews(\n    h: FullViewHolder,\n    item: MatchItem,\n    isExpanded: Boolean\n  ) {\n      // bind views that are visible when expanded and collapsed\n  }\n  \n  private funbindExpandedExtraViews(\n    h: FullViewHolder,\n    item: MatchItem\n  ) {\n      // bind views that are only shown when the item is expanded\n  }\n\n  \n\n  private fun toggleExpanded(\n    h: FullViewHolder\n  ) {\n    if (h.adapterPosition< 0) return // touch event can technically fire after a view is unbound\n\n    val autoTransition = AutoTransition()\n    \n    val item = items[position]\n    item.isExpanded = !item.isExpanded\n    \n    bindGeneralViews(h, item, newIsExpanded)\n    if (item.isExpanded) {\n      bindExpandedExtraViews(h, item)\n  \n      autoTransition.ordering = AutoTransition.ORDERING_TOGETHER\n      autoTransition.duration = ANIMATION_DURATION_MS\n      TransitionManager.beginDelayedTransition(h.rootView, autoTransition)\n      h.expandedConstraintSet.applyTo(h.rootView)\n  \n      notifyItemChanged(h.adapterPosition, Unit)\n    } else {\n      autoTransition.ordering = AutoTransition.ORDERING_TOGETHER\n      autoTransition.duration = ANIMATION_DURATION_MS\n      TransitionManager.beginDelayedTransition((h.rootView.parent as ViewGroup), autoTransition)\n      notifyItemChanged(h.adapterPosition, Unit)\n    }\n  }\n}\n\ndata class MatchItem(\n...\n) {\n  // Exclude this field from equals/hachcode by declaring it in class body\n  var isExpanded: Boolean = false\n}\n\nprivate class FullViewHolder (itemView: View) : RecyclerView.ViewHolder(itemView) {\n  ...\n\n  val collapsedConstraintSet: ConstraintSet = ConstraintSet()\n  val expandedConstraintSet: ConstraintSet = ConstraintSet()\n  \n  init {\n    collapsedConstraintSet.clone(rootView)\n    expandedConstraintSet.clone(rootView.context, R.layout.build_full_item)\n  }\n}\n
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它是如何工作的？

\n

该代码严重依赖于notifyItemChanged(Int, Payload)和TransitionManager.beginDelayedTransition()。首先让\xe2\x80\x99s 回顾一下它们是如何工作的。

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首先，notifyItemChanged(Int, Payload)将确保传递给的视图持有者onBindViewHolder(RecyclerView.ViewHolder, Int, MutableList<Any>)与当前绑定的视图持有者是同一视图持有者。例如。let\xe2\x80\x99s 表示A当前绑定到项目 0 的视图持有者。如果我们调用，notifyItemChanged(0, Unit)那么我们可以保证它将A被传递到onBindViewHolder(RecyclerView.ViewHolder, Int, MutableList<Any>)。除此之外，RecyclerView 非常擅长对项目视图高度的变化进行动画处理，因此notifyItemChanged()会通知 RecyclerView 检查高度是否发生变化，以及是否必须播放一个漂亮的动画来使其他项目向上或向下移动。

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其次，TransitionManager.beginDelayedTransition()对传入的视图的当前状态进行快照。然后ConstraintSet.applyTo()，当调用时，将计算保存的状态和当前状态之间的差异，并自动应用动画来在两者之间进行转换。

\n

现在基础知识已经不存在了。以下是展开和折叠项目的工作原理。

\n

对于扩展项目：

\n
    \n
  1. 用户点击项目。
    2. \n
  2. toggleExpanded()叫做。
    3. \n
  3. Item\xe2\x80\x99s 视图状态更新为展开。
    4. \n
  4. 我们将所有视图预先绑定到视图持有者，以便在动画过程中不会发生闪烁，并且所有视图都完全绑定。
    5. \n
  5. 调用 TransitionManager.beginDelayedTransition() 来拍摄项目视图状态的快照。
    6. \n
  6. ConstraintSet.applyTo()被调用以将我们的扩展布局应用到视图并以动画方式进行更改。
    7. \n
  7. notifyItemChanged(h.``adapterPosition``, Unit)叫做。这保证了当调用 onBindViewHolder 时，我们会将完全绑定的视图持有者传递给我们。另外，它通知recyclerview项目的高度已经改变，让recyclerview处理高度变化的动画。
    8. \n
\n

对于折叠项目：

\n
    \n
  1. 用户点击项目。
    2. \n
  2. toggleExpanded()叫做。
    3. \n
  3. Item\xe2\x80\x99s 视图状态更新为折叠。
    4. \n
  4. 调用 TransitionManager.beginDelayedTransition() 来拍摄项目视图状态的快照。
    5. \n
  5. notifyItemChanged(h.``adapterPosition``, Unit)叫做。这保证了当调用 onBindViewHolder 时，我们会将完全绑定的视图持有者传递给我们。另外，它通知recyclerview项目的高度已经改变，让recyclerview处理高度变化的动画。
    6. \n
  6. ConstraintSet.applyTo()被调用以将折叠布局应用于视图并以动画方式进行更改。
    7. \n
\n

其他有趣的事实

\n

折叠一个物品实际上比看上去要复杂得多。TransitionManager.beginDelayedTransition()之前的通话至关重要notifyItemChanged(h.adapterPosition, Unit)。onBindViewHolder这是因为由于 recyclerview 的实现方式，传递给的视图持有者始终未绑定。

\n

为什么这是一个问题？好吧，这意味着如果我们改为调用TransitionManager.beginDelayedTransition()，onBindViewHolder它将保存的状态是视图未绑定。当ConstraintSet.applyTo()调用时，它将在未绑定视图和绑定视图之间进行动画处理，默认动画是使视图淡入。这不是我们想要的，而且动画看起来非常难看。

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