我想做的简单的事情（见图片）
显示一个包含来自firebase中两个不同位置的信息的视图，以便它以专业的方式上下滚动
我有一个电影列表，在每个列表上，我希望用户指定一个分级并查看它
在数据库中，我创建了两个结构，一边是电影列表，另一边是每个用户的收视率
使用FirebaseRecyclerAdapter时出现问题
我的问题是，快速上下滚动列表，来自第二个引用（评级）的信息的可视化将加载到不同的时间（异步调用），这是不可接受的（小）延迟构建视图。这是firebasecyclerview的限制吗？
因为viewholders在recycleview中被重用，所以每次在populateview（）中重置并重新加载额定值，这没有帮助。一旦检索到，如果用户滚动视图，我就不得不再次获取它们（请参阅populateview（）中的setonListener）
在populateView中设置监听器也会导致监听器的数量与执行populateView（）的次数相同（如果上下滚动多次）。
解决方案/解决方案？
有没有正确的方法来预防这个问题？或者是一种限制？
如果侦听器位于populateView（）中，并且创建了许多侦听器，那么我的实现的性能如何？
下面是我正在思考的一些事情：
防止取景器被回收，只装一次？
重写其他一些RecyclerView方法？我试过parseSnapshot（），但问题是一样的…
将数据库结构更改为将所有信息放在一个列表中（我认为这不是一个好的列表，因为这意味着将每个用户的分级信息添加到电影列表中）
在评级部分添加一个加载微调器，以便评级仅在完成对firebase的异步调用（不喜欢）时显示，而不会产生“在用户面前更改星形颜色”的今日效果。
我的实现
来自FirebaseRecyclerAdapter
@Override
protected void populateViewHolder(final MovieViewHolder viewHolder, final Movie movie, final int position) {
String movieId = this.getRef(position).getKey();
// Oblidged to show no rating at the beginning because otherwise
// if a viewHolder is reused it has the values from another movie
viewHolder.showNoRating();
//---------------------------------------------
// Set values in the viewHolder from the model
//---------------------------------------------
viewHolder.movieTitle.setText(movie.getTitle());
viewHolder.movieDescription.setText(movie.getDescription());
//-----------------------------------------------------
// Ratings info are in another DB location... get them
// but call is asynchronous so PROBLEM when SCROLLING!
//-----------------------------------------------------
DatabaseReference ratingMovieRef = mDbRef.child(Constants.FIREBASE_LOCATION_RATINGS).child(currentUserId).child(movieId);
ratingQuoteRef.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
RatingMovie ratingMovie = dataSnapshot.getValue(RatingMovie.class);
Rating rating = Rating.NO_RATING;
if (ratingMovie != null) {
rating = Rating.valueOf(ratingMovie.getRating());
}
// Set the rating in the viewholder (through anhelper method)
viewHolder.showActiveRating(rating);
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
来自影迷
public class QuoteViewHolder extends RecyclerView.ViewHolder {
public CardView cardView;
public TextView movieTitle;
public TextView movieDescription;
public ImageView ratingOneStar;
public ImageView ratingTwoStar;
public ImageView ratingThreeStar;
public QuoteViewHolder(View itemView) {
super(itemView);
movieTitle = (TextView)itemView.findViewById(R.id.movie_title);
movieDescription = (TextView)itemView.findViewById(R.id.movie_descr);
// rating
ratingOneStar = (ImageView)itemView.findViewById(R.id.rating_one);
ratingTwoStar = (ImageView)itemView.findViewById(R.id.rating_two);
ratingThreeStar = (ImageView)itemView.findViewById(R.id.rating_three);
}
/**
* Helper to show the color on stars depending on rating value
*/
public void showActiveRating(Rating rating){
if (rating.equals(Rating.ONE)) {
// just set the good color on ratingOneStar and the others
...
}
else if (rating.equals(Rating.TWO)) {
// just set the good color
...
} else if (rating.equals(Rating.THREE)) {
// just set the good color
...
}
/**
* Initialize the rating icons to unselected.
* Important because the view holder can be reused and if not initalised values from other moviecan be seen
*/
public void initialiseNoRating(){
ratingOneStar.setColorFilter(ContextCompat.getColor(itemView.getContext(), R.color.light_grey));
ratingTwoStar.setColorFilter(....
ratingThreeStar.SetColorFilter(...
}
最佳答案
您可以使用childeventlistener对分级进行排序缓存。基本上只需要为ratings节点创建一个单独的节点，并让它将ratings存储在一个映射中。然后使用recycleradapter，如果评分可用，您将从地图中检索，如果不可用，则让评分侦听器在下载评分后立即更新recyclerview。这是一个策略，你可以着手去做，你将不得不从firebaseui库中手动复制/粘贴一些类，并设置一些公共字段以使其工作。
用法如下
private MovieRatingConnection ratingConnection;
// inside onCreate
ratingConnection = new MovieRatingConnection(userId, new MovieRatingConnection.RatingChangeListener() {
@Override
public void onRatingChanged(DataSnapshot dataSnapshot) {
if (recyclerAdapter != null) {
if (dataSnapshot != null) {
int index = recyclerAdapter.snapshots.getIndexForKey(dataSnapshot.getKey());
recyclerAdapter.notifyItemChanged(index);
}
}
}
});
Query movieQuery = FirebaseDatabase.getInstance().getReference().child("Movies");
recyclerAdapter = new FirebaseRecyclerAdapter(movieQuery...) {
@Override
public void populateViewHolder(RecyclerView.ViewHolder viewHolder, Object model, int position) {
//...
final String key = getRef(position).getKey();
viewHolder.showActiveRating(ratingConnection.getRating(key));
}
};
而movieratingconnection就是这样一个类
public class MovieRatingConnection {
private MovieRatingListener listener;
public MovieRatingConnection(String userId, RatingChangeListener changeListener) {
Query query = FirebaseDatabase.getInstance().getReference().child("MovieRatings").child(userId);
listener = new MovieRatingListener(query, changeListener);
}
public Rating getRating(String key) {
return listener.getRating(key);
}
public void cleanup() {
if (listener != null) {
listener.unregister();
}
}
public static class MovieRatingListener implements ChildEventListener {
public interface RatingChangeListener {
public void onRatingChanged(DataSnapshot snapshot);
}
private Query query;
private HashMap<String, Rating> ratingMap = new HashMap<>();
private RatingChangeListener changeListener;
public MovieRatingListener(Query query, RatingChangeListener changeListener) {
this.query = query;
this.changeListener = changeListener;
query.addChildEventListener(this);
}
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot != null) {
ratingMap.put(dataSnapshot.getKey(), dataSnapshot.getValue(Rating.class));
changeListener.onRatingChanged(dataSnapshot);
}
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot != null) {
ratingMap.put(dataSnapshot.getKey(), dataSnapshot.getValue(Rating.class));
changeListener.onRatingChanged(dataSnapshot);
}
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
ratingMap.remove(dataSnapshot.getKey());
changeListener.onRatingChanged(null);
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
public Rating getRating(String key) {
if (ratingMap.get(key) != null) {
return ratingMap.get(key);
} else {
return new Rating(); // default value/null object
}
}
public void unregister() {
query.removeEventListener(this);
}
}
}