我试图创建一个RecyclerView来从Firebase接收排序的用户密钥，然后根据排序的数据查找用户并显示它们。
我第一次启动活动时，它完全是空白的，并且没有到达给适配器提供数据的onChildAdded方法。但是，如果我退出并返回该活动，那么从那里开始一切都很好。
我尝试将代码放在onChildAdded中，放入onChildChaned中，但是这会在用户有任何更新时触发，并且列表中填充了重复项。
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_leaderboards);
recyclerView = findViewById(R.id.my_recycler_view);
// use this setting to improve performance if you know that changes
// in content do not change the layout size of the RecyclerView
// use a linear layout manager
layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
this.sorted = new ArrayList<>();
FirebaseDatabase database = FirebaseDatabase.getInstance();
this.user = FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference stepsRef = database.getReference("Steps");
stepsRef.orderByValue().addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
userKeys.clear();
for(DataSnapshot ds : dataSnapshot.getChildren()) {
userKeys.add(ds.getKey());
}
Log.v("help", userKeys.toString());
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
DatabaseReference usersRef = database.getReference("Users");
usersRef.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
for(int i = 0; i < userKeys.size(); i++) {
Log.v("number " + i, userKeys.get(i));
if(dataSnapshot.getKey().equals(userKeys.get(i))) {
Log.v("aaaaa", "aaaa");
User user = dataSnapshot.getValue(User.class);
users.add(user);
Log.v("username", users.get(0).getFirstName());
}
}
ArrayList<User> sorted = new ArrayList<>();
for(int i = 0; i < userKeys.size(); i++) {
for(int j = 0; j < users.size(); j++) {
User user = users.get(j);
if(user.getId().equals(userKeys.get(i))) {
sorted.add(user);
mAdapter.notifyDataSetChanged();
}
}
}
if(mAdapter == null) {
mAdapter = new LeaderboardsAdapter(sorted);
Log.v("plshelp", sorted.toString());
recyclerView.setAdapter(mAdapter);
} else {
((LeaderboardsAdapter)mAdapter).updateData(sorted);
}
}
@Override
public void onChildChanged(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onChildRemoved(@NonNull DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(@NonNull DataSnapshot dataSnapshot, @Nullable String s) {
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
mAdapter = new LeaderboardsAdapter(sorted);
recyclerView.setAdapter(mAdapter);
}
有没有办法让适配器在第一次启动时加载数据？