java - RecyclerView 中的 SmoothScroller

Question

我有以下布局:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/item"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="#fafafa"
    android:orientation="vertical"
    android:paddingBottom="16dp"
    android:paddingEnd="16dp"
    android:paddingLeft="16dp"
    android:paddingStart="16dp">

    <View
        android:id="@+id/item_divider"
        android:layout_width="match_parent"
        android:layout_height="1dp"
        android:layout_marginBottom="16dp"
        android:background="#D3D3D3" />

    <TextView
        android:id="@+id/item_title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="#000"
        android:textSize="22sp"
        tools:text="Léon: The Professional" />

    <LinearLayout
        android:id="@+id/sub_item"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:orientation="vertical">

        <TextView
            android:id="@+id/sub_item_genre"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="18sp"
            tools:text="Genre:  Crime, Drama, Thriller" />

        <TextView
            android:id="@+id/sub_item_year"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:textSize="18sp"
            tools:text="Year: 1993" />
    </LinearLayout>
</LinearLayout>

在我的 recyclerview 适配器中:

@Override
public void onBindViewHolder(RecViewHolder holder, int position) {
        Movie movie = list.get(position);

        boolean expanded = movie.isExpanded();
        subItem.setVisibility(expanded ? View.VISIBLE : View.GONE);

        holder.title.setOnClickListener(v -> {
            boolean expanded = movie.isExpanded();
            movie.setExpanded(!expanded);
            notifyItemChanged(position);
        });
 }

正如您在代码中看到的，当您单击某个项目时，子项目会隐藏/显示。

我想要实现的是:当您单击列表中的最后一项时，我希望它显示整行(包括子项)。目前它将可见性更改为 VISIBLE，但是该行的 subItem 对用户是不可见的直到用户滚动到它。

在下图中，God Father 是最后一个可见项。如何显示整行包括 God Father 作为标题和子项 当用户单击时？

Answer 1

如果滚动到 RecyclerView 扩展项的底部，问题就会解决。关键点是使用 LinearSmoothScroller 进行滚动。试试下面的代码:

public class RecAdapter extends RecyclerView.Adapter<RecAdapter.RecViewHolder> {

    private List<Movie> list;
    private RecyclerView mRecyclerView;
    private RecyclerView.SmoothScroller mSmoothScroller;

    public RecAdapter(List<Movie> list) {
        this.list = list;
    }

    @Override
    public RecViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater
                .from(parent.getContext())
                .inflate(R.layout.item_movie, parent, false);
        return new RecViewHolder(view);
    }

    @Override
    public void onBindViewHolder(RecViewHolder holder, int position) {
        Movie movie = list.get(position);

        holder.bind(movie);

        holder.itemView.setOnClickListener(v -> {
            boolean expanded = movie.isExpanded();
            movie.setExpanded(!expanded);
            notifyItemChanged(position);

            if (movie.isExpanded()) {
                mSmoothScroller.setTargetPosition(position);
                new Handler().postDelayed(() -> mRecyclerView.getLayoutManager().startSmoothScroll(mSmoothScroller), 100);
            }
        });
    }

    @Override
    public int getItemCount() {
        return list == null ? 0 : list.size();
    }

    @Override
    public void onAttachedToRecyclerView(RecyclerView recyclerView) {
        super.onAttachedToRecyclerView(recyclerView);
        mRecyclerView = recyclerView;

        mSmoothScroller = new LinearSmoothScroller(recyclerView.getContext()) {
            @Override
            protected int getVerticalSnapPreference() {
                return LinearSmoothScroller.SNAP_TO_ANY;
            }

            @Override
            protected float calculateSpeedPerPixel(DisplayMetrics displayMetrics) {
                return 150f / displayMetrics.densityDpi;
            }
        };
    }

    public class RecViewHolder extends RecyclerView.ViewHolder {

        private TextView title;
        private TextView genre;
        private TextView year;
        private View subItem;

        public RecViewHolder(View itemView) {
            super(itemView);

            title = itemView.findViewById(R.id.item_title);
            genre = itemView.findViewById(R.id.sub_item_genre);
            year = itemView.findViewById(R.id.sub_item_year);
            subItem = itemView.findViewById(R.id.sub_item);
        }

        private void bind(Movie movie) {
            boolean expanded = movie.isExpanded();

            subItem.setVisibility(expanded ? View.VISIBLE : View.GONE);

            title.setText(movie.getTitle());
            genre.setText("Genre: " + movie.getGenre());
            year.setText("Year: " + movie.getYear());
        }
    }
}

结果如下: