从列表中删除项目而不是从RecyclerView中删除它们？

Question

When I remove an itemfrom my list, it does not get removed from the RecyclerView at all.

Here is how I remove ( user.getUid() does equal dataSnaphot.getkey() ):

for(User user: mFriendList){
    if(user.getUid().equals(dataSnapshot.getKey())){
        mFriendList.remove(user);
    }
}
friendAdapter.notifyDataSetChanged();

My User object gets removed from the list but not from the view. When I use the same method for adding itemsto the list, like..

mFriendList.add(user);
friendAdapter.notifyDataSetChanged();

..it does get added to the list and view as well. Why is it not working well with removing from the list?

EDIT:

Setting up RecyclerView (inside a Fragment):

mRecyclerView = (EmptyRecyclerView) rootView.findViewById(R.id.contactRecyclerView);
mRecyclerView.setHasFixedSize(true);

View myView = rootView.findViewById(R.id.emptyAdapterList);
mRecyclerView.setEmptyView(myView);

mLinearLayoutManager = new LinearLayoutManager(getContext());
mRecyclerView.setLayoutManager(mLinearLayoutManager);

mFriendList = new ArrayList<User>();

friendAdapter = new FriendAdapter(mFriendList, getContext());
mRecyclerView.setAdapter(friendAdapter);

Answer 1

Removing items in foreach loop may cause undefined behavior depending on the collection.

Instead of calling remove method directly while iterating over collection You have four options:

• use Iterator :

final Iterator<User> iterator = mFriendList.iterator();
while(iterator.hasNext()) {
    final User user = iterator.next();
    if(user.getUid().equals(dataSnapshot.getKey())) {
        iterator.remove();
    }
}

• create another collection, collect all items that you'd like to remove and then removeAll() items:

final Collection toRemove = new ArrayList<User>();
for(User user: mFriendList){
    if(user.getUid().equals(dataSnapshot.getKey())){
        toRemove.add(user);
    }
}
mFriendList.removeAll(toRemove);

• use Java 8 (or Stream Support) Streams API, especially filter() method:

mFriendList = mFriendList.stream()
    .filter(user -> !user.getUid().equals(dataSnapshot.getKey()))
    .collect(Collectors.toList());

• use RxJava (or RxJava 2) filtering:

mFriendList =  Single.just(mFriendList)
    .flatMapIterable(identity()) // list -> list
    .filter(user -> !user.getUid().equals(dataSnapshot.getKey()))
    .toList()
    .blockingGet(); // or whatever transformation

Depends on whether you are using reactive approach or not I strongly recommend to use the latest one for consistency or just to remove dependencies from Stream Support libraries if you are targeting old enough Android SDK.

Keep in mind you have to notifyDataSetChanged() as soon as you will finish your modifications.

Answer 2

Given the limited info provided by your code my best guess would be that your removal fails since your data source is unaffected by your removed item from the list. If that's not it provide more code and I' wld be happy to help