android - TransitionManager 不动画颜色变化

Question

我关注了Nick Butcher's Material Improvements I/O 2016 talk ，大约在 6:00，他开始谈论动画列表项。我已经完全按照他的方式实现了该功能，并且绑定(bind)更改正确地设置了动画，但是颜色更改没有设置动画，尽管他明确表示他们会:

代码如下:

这是 RecyclerView.Adapter 类的相关部分:

override fun onBindViewHolder(holder: ViewHolder, position: Int) {
    val item: Pair<String, String> = items[position]

    holder.title.text = item.first
    holder.subtitle.text = item.second

    val isExpanded = position == expandedPosition
    holder.subtitle.visibility = if (isExpanded) View.VISIBLE else View.GONE
    holder.itemView.isActivated = isExpanded
    holder.itemView.setOnClickListener {
        expandedPosition = if (isExpanded) -1 else position
        TransitionManager.beginDelayedTransition(recyclerView)
        notifyDataSetChanged()
    }
}

这是我为项目使用的布局。 ConstraintLayout 对于当前的布局设置有点矫枉过正，但我​​减少了布局以创建一个最小的示例。

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    tools:context=".MainActivity"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/item_background"
    android:stateListAnimator="@animator/item_elevation"
    android:padding="8dp">

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textSize="24sp"
        tools:text="Title 1"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintStart_toStartOf="parent"/>

    <TextView
        android:id="@+id/subtitle"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        tools:text="Subtitle 1"
        app:layout_constraintTop_toBottomOf="@id/title"
        app:layout_constraintStart_toStartOf="parent"
        />

</android.support.constraint.ConstraintLayout>

这是我用于项目布局的背景:

<selector xmlns:android="http://schemas.android.com/apk/res/android"
    android:enterFadeDuration="@android:integer/config_mediumAnimTime"
    android:exitFadeDuration="@android:integer/config_mediumAnimTime">

    <item android:state_activated="true"
        android:drawable="@color/colorAccent" />

    <item android:drawable="@color/colorPrimaryDark" />

</selector>

Answer 1

确保您的数据集具有稳定的 ID 并调用 Recycler.Adapter#setHasStableIds(true)。看 setHasStableIds() .

您还需要覆盖 getItemId()在适配器中返回一个稳定的 id。另见 notifyDataSetChanged有关稳定 ID 的简短讨论。

RecyclerView will attempt to synthesize visible structural change events for adapters that report that they have stable IDs when this method is used. This can help for the purposes of animation and visual object persistence but individual item views will still need to be rebound and relaid out.

这是一个将稳定 ID 设置为 false 的演示:

并将稳定的 ID 设置为 true。我在颜色变化上设置了很长的过渡时间，所以它会很明显。

RecyclerViewAdapter.java

这是演示中使用的适配器。 TransitionManager.beginDelayedTransition(mRecyclerView) 已被删除，让 RecyclerView 更好地处理动画。

class RecyclerViewAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    RecyclerViewAdapter() {
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view;
        view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_layout, parent, false);
        return new ItemViewHolder(view);
    }

    private int mExpandedPosition = RecyclerView.NO_POSITION;

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        final ItemViewHolder vh = (ItemViewHolder) holder;
        final TextView subTitle = vh.mSubTitle;

        vh.mTitle.setText(titleForPosition(position));
        subTitle.setText(subTitleForPosition(position));

        final boolean isExpanded = position == mExpandedPosition;

        subTitle.setVisibility((isExpanded) ? View.VISIBLE : View.GONE);
        holder.itemView.setActivated(isExpanded);
        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                mExpandedPosition = isExpanded ? RecyclerView.NO_POSITION : vh.getAdapterPosition();
                notifyDataSetChanged();
            }
        });
    }

    private String titleForPosition(int position) {
        return "Title " + position;
    }

    private String subTitleForPosition(int position) {
        return "Subtitle " + position;
    }

    @Override
    public int getItemCount() {
        return 5;
    }

    @Override
    public long getItemId(int position) {
        return titleForPosition(position).hashCode();
    }

    static class ItemViewHolder extends RecyclerView.ViewHolder {
        private final TextView mTitle;
        private final TextView mSubTitle;

        ItemViewHolder(View itemView) {
            super(itemView);
            mTitle = itemView.findViewById(R.id.title);
            mSubTitle = itemView.findViewById(R.id.subtitle);
        }
    }

    @SuppressWarnings("unused")
    private final static String TAG = "RecyclerViewAdapter";
}