/**
 * 分組的ViewHolder
 */
public class TeamViewHolder extends ParentViewHolder {
 /**
  * Default constructor.
  *
  * @param itemView The {@link View} being hosted in this ViewHolder
  */
 public TeamViewHolder(@NonNull View itemView) {
  super(itemView);
 }
}

public class PlayerViewHolder extends ChildViewHolder {
 private final TextView mIngredientTextView;

 /**
  * Default constructor.
  *
  * @param itemView The {@link View} being hosted in this ViewHolder
  */
 public PlayerViewHolder(@NonNull View itemView) {
  super(itemView);
  mIngredientTextView = ((TextView) itemView.findViewById(R.id.ingredient_textview));
 }
}

public class TeamAdapter extends ExpandableRecyclerAdapter<Team, Player, TeamViewHolder, PlayerViewHolder> {
 private final LayoutInflater mInflater;

 /**
  * Primary constructor. Sets up {@link #mParentList} and {@link #mFlatItemList}.
  * <p>
  * Any changes to {@link #mParentList} should be made on the original instance, and notified via
  * {@link #notifyParentInserted(int)}
  * {@link #notifyParentRemoved(int)}
  * {@link #notifyParentChanged(int)}
  * {@link #notifyParentRangeInserted(int, int)}
  * {@link #notifyChildInserted(int, int)}
  * {@link #notifyChildRemoved(int, int)}
  * {@link #notifyChildChanged(int, int)}
  * methods and not the notify methods of RecyclerView.Adapter.
  *
  * @param parentList List of all parents to be displayed in the RecyclerView that this
  *     adapter is linked to
  */
 public TeamAdapter(Context context, @NonNull List<Team> parentList) {
  super(parentList);
  mInflater = LayoutInflater.from(context);
 }

 @NonNull
 @Override
 public TeamViewHolder onCreateParentViewHolder(@NonNull ViewGroup parentViewGroup, int viewType) {
  View view = mInflater.inflate(R.layout.team_view, parentViewGroup, false);
  return new TeamViewHolder(view);
 }

 @NonNull
 @Override
 public PlayerViewHolder onCreateChildViewHolder(@NonNull ViewGroup childViewGroup, int viewType) {
  View view = mInflater.inflate(R.layout.player_view, childViewGroup, false);
  return new PlayerViewHolder(view);
 }

 @Override
 public void onBindParentViewHolder(@NonNull TeamViewHolder parentViewHolder, int parentPosition, @NonNull Team parent) {
  parentViewHolder.bind(parent);
 }

 @Override
 public void onBindChildViewHolder(@NonNull PlayerViewHolder childViewHolder, int parentPosition, int childPosition, @NonNull Player child) {
  childViewHolder.bind(child);
 }
}

// 首先要給recyclerview設(shè)置一個布局管理器
recyclerView.setLayoutManager(new LinearLayoutManager(this));

// 第一個球隊的所有球員
List<Player> players1 = new ArrayList<>();
// 第二個球隊的所有球員
List<Player> players2 = new ArrayList<>();
// 第三個球隊的所有球員
List<Player> players3 = new ArrayList<>();

// 所有球隊的集合
List<Team> teams = new ArrayList<>();
// 創(chuàng)建每個球隊，傳入的參數(shù)是隊名跟隊員
Team team = new Team(teamNames[0], players1);
Team team2 = new Team(teamNames[1], players2);
Team team3 = new Team(teamNames[2], players3);
teams.add(team);
teams.add(team2);
teams.add(team3);
// adapter傳入的數(shù)據(jù)源是所有球隊的集合
TeamAdapter adapter = new TeamAdapter(this, teams);
  recyclerView.setAdapter(adapter);

private static final float INITIAL_POSITION = -90F;
private static final float ROTATED_POSITION = 0.0F;
@Override
 public void setExpanded(boolean expanded) {
  super.setExpanded(expanded);
  RotateAnimation ra;
  if (!expanded) {
   // 由展開到收起狀態(tài)
   ra = new RotateAnimation(
     ROTATED_POSITION, // 展開狀態(tài)角度
     INITIAL_POSITION, // 收起狀態(tài)角度
     RotateAnimation.RELATIVE_TO_SELF, // 相對于自己的中心點
     0.5f,
     Animation.RELATIVE_TO_SELF,
     0.5f);
  } else {
   ra = new RotateAnimation(
     INITIAL_POSITION,
     ROTATED_POSITION,
     Animation.RELATIVE_TO_SELF,
     0.5f,
     Animation.RELATIVE_TO_SELF,
     0.5f);
  }
  ra.setDuration(200);
  ra.setFillAfter(true);
  mArrowExpandImageView.startAnimation(ra);
 }