因此,我在Java.util.ArrayList $ Itr.next(ArrayList.java:860)处收到“ java.util.ConcurrentModificationException”错误。
我知道收到此错误的原因是因为我在向该列表添加对象的同时迭代了一个列表。但是,我不知道如何添加listIterator来解决此问题。
[如果有人可以向我展示如何添加迭代器,那就太好了。谢谢!
我已经在我的代码中指出了错误的开始位置
//method to evaluate who you have chatted with and display on screen
private void readChats() {
users = new ArrayList<>();
reference = FirebaseDatabase.getInstance().getReference("USERS");
reference.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
users.clear();
//gets every user snapshot from "USERS" children in firebase and make User obj
for(DataSnapshot snapshot : dataSnapshot.getChildren()) {
User user = snapshot.getValue(User.class);
//for every ID that was stored in textTransacRec list
for (String ID : textTransacRec) {
//out of all existing users in firebase if a user's ID matches any of the ID's in textTransacRec
if(user.getID().equals(ID)) {
//if there are any User objects inside users list
if(users.size() != 0) {
//check to see if the user already exists in list or not by matching w/ existing user ID's
//if there is no ID match then user does not exist --> add to users list to display
//---------------------------ERROR STARTS FROM HERE----------------------
for(User u : users) {
if(!user.getID().equals(u.getID())) {
users.add(user);
}
}
}
//if no User objects inside users list --> add to users list
else {
users.add(user);
}
}
}
}
chatRecyclerAdap = new ChatRecyclerAdap(getContext(), users);
recyclerView.setAdapter(chatRecyclerAdap);
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
ListIterator具有add方法,您可以像这样使用它:
ListIterator<User> iterator = users.listIterator();
while(iterator.hasNext()) {
User u = iterator.next();
if(!user.getID().equals(u.getID())) {
iterator.add(user);
}
}
但是要仅当列表中不存在该用户时,才需要添加迭代器。如果您在循环内执行此操作,则在列表中的任何一个用户没有相同ID的情况下,您都会添加一个用户。但是,您需要检查所有这些设置是否正确。如果您使用的是Java 8,则可以执行以下操作:
boolean userExists = users.stream().filter(u -> u.getID().equals(user.getID())).findFirst().isPresent();
if (!userExists) {
users.add(user);
}