What is the SortedList<T> working with RecyclerView.Adapter?

SortedList handles the communication to the Recycler adapter via Callback.

One difference between SortedList and List is seen in the addAll helper method in the sample below.

public void addAll(List<Page> items) {
        mPages.beginBatchedUpdates();
        for (Page item : items) {
            mPages.add(item);
        }
        mPages.endBatchedUpdates();
    }

Keeps last added item

Say I have 10 cached items to load immediately when my recycler list is populated. At the same time, I query my network for the same 10 items because they could have changed since I cached them. I can call the same addAll method and SortedList will replace the cachedItems with fetchedItems under the hood (always keeps the last added item).

// After creating adapter
myAdapter.addAll(cachedItems)
// Network callback
myAdapter.addAll(fetchedItems)

In a regular List, I would have duplicates of all my items (list size of 20). With SortedList its replaces items that are the same using the Callback's areItemsTheSame.

Its smart about when to update the Views

When the fetchedItems are added, onChange will only be called if one or more of the Page's title changed. You can customize what SortedList looks for in the Callback's areContentsTheSame.

Its performant

If you are going to add multiple items to a SortedList, BatchedCallback call convert individual onInserted(index, 1) calls into one onInserted(index, N) if items are added into consecutive indices. This change can help RecyclerView resolve changes much more easily.

Sample

You can have a getter on your adapter for your SortedList, but I just decided to add helper methods to my adapter.

Adapter Class:

  public class MyAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
    private SortedList<Page> mPages;

    public MyAdapter() {
        mPages = new SortedList<Page>(Page.class, new SortedList.Callback<Page>() {
            @Override
            public int compare(Page o1, Page o2) {
                return o1.getTitle().compareTo(o2.getTitle());
            }

            @Override
            public void onInserted(int position, int count) {
                notifyItemRangeInserted(position, count);
            }

            @Override
            public void onRemoved(int position, int count) {
                notifyItemRangeRemoved(position, count);
            }

            @Override
            public void onMoved(int fromPosition, int toPosition) {
                notifyItemMoved(fromPosition, toPosition);
            }

            @Override
            public void onChanged(int position, int count) {
                notifyItemRangeChanged(position, count);
            }

            @Override
            public boolean areContentsTheSame(Page oldItem, Page newItem) {
                // return whether the items' visual representations are the same or not.
                return oldItem.getTitle().equals(newItem.getTitle());
            }

            @Override
            public boolean areItemsTheSame(Page item1, Page item2) {
                return item1.getId() == item2.getId();
            }
        });

    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(parent.getContext())
                .inflate(R.layout.viewholder_page, parent, false);
        return new PageViewHolder(view);
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        PageViewHolder pageViewHolder = (PageViewHolder) holder;
        Page page = mPages.get(position);
        pageViewHolder.textView.setText(page.getTitle());
    }

    @Override
    public int getItemCount() {
        return mPages.size();
    }

    // region PageList Helpers
    public Page get(int position) {
        return mPages.get(position);
    }

    public int add(Page item) {
        return mPages.add(item);
    }

    public int indexOf(Page item) {
        return mPages.indexOf(item);
    }

    public void updateItemAt(int index, Page item) {
        mPages.updateItemAt(index, item);
    }

    public void addAll(List<Page> items) {
        mPages.beginBatchedUpdates();
        for (Page item : items) {
            mPages.add(item);
        }
        mPages.endBatchedUpdates();
    }

    public void addAll(Page[] items) {
        addAll(Arrays.asList(items));
    }

    public boolean remove(Page item) {
        return mPages.remove(item);
    }

    public Page removeItemAt(int index) {
        return mPages.removeItemAt(index);
    }

    public void clear() {
       mPages.beginBatchedUpdates();
       //remove items at end, to avoid unnecessary array shifting
       while (mPages.size() > 0) {
          mPages.removeItemAt(mPages.size() - 1);
       }
       mPages.endBatchedUpdates();
    }
}

Page class:

public class Page {
    private String title;
    private long id;

    public String getTitle() {
        return title;
    }

    public void setTitle(String title) {
        this.title = title;
    }

    public long getId() {
        return id;
    }

    public void setId(long id) {
        this.id = id;
    }
}

Viewholder xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

    <TextView
        android:id="@+id/text_view"
        style="@style/TextStyle.Primary.SingleLine"
        android:layout_width="match_parent"
        android:layout_height="wrap_content" />

</LinearLayout>

Viewholder class:

public class PageViewHolder extends RecyclerView.ViewHolder {
    public TextView textView;


    public PageViewHolder(View itemView) {
        super(itemView);
        textView = (TextView)item.findViewById(R.id.text_view);
    }
}

SortedList is in v7 support library.

A SortedList implementation that can keep items in order and also notify for changes in the list such that it can be bound to a RecyclerView.Adapter.

It keeps items ordered using the compare(Object, Object) method and uses binary search to retrieve items. If the sorting criteria of your items may change, make sure you call appropriate methods while editing them to avoid data inconsistencies.

You can control the order of items and change notifications via the SortedList.Callback parameter.

Here below is a sample of use of SortedList, I think it is what you want, take a look at it and enjoy!

public class SortedListActivity extends ActionBarActivity {
    private RecyclerView mRecyclerView;
    private LinearLayoutManager mLinearLayoutManager;
    private SortedListAdapter mAdapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.sorted_list_activity);
        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);
        mRecyclerView.setHasFixedSize(true);
        mLinearLayoutManager = new LinearLayoutManager(this);
        mRecyclerView.setLayoutManager(mLinearLayoutManager);
        mAdapter = new SortedListAdapter(getLayoutInflater(),
                new Item("buy milk"), new Item("wash the car"),
                new Item("wash the dishes"));
        mRecyclerView.setAdapter(mAdapter);
        mRecyclerView.setHasFixedSize(true);
        final EditText newItemTextView = (EditText) findViewById(R.id.new_item_text_view);
        newItemTextView.setOnEditorActionListener(new TextView.OnEditorActionListener() {
            @Override
            public boolean onEditorAction(TextView textView, int id, KeyEvent keyEvent) {
                if (id == EditorInfo.IME_ACTION_DONE &&
                        (keyEvent == null || keyEvent.getAction() == KeyEvent.ACTION_DOWN)) {
                    final String text = textView.getText().toString().trim();
                    if (text.length() > 0) {
                        mAdapter.addItem(new Item(text));
                    }
                    textView.setText("");
                    return true;
                }
                return false;
            }
        });
    }

    private static class SortedListAdapter extends RecyclerView.Adapter<TodoViewHolder> {
        SortedList<Item> mData;
        final LayoutInflater mLayoutInflater;
        public SortedListAdapter(LayoutInflater layoutInflater, Item... items) {
            mLayoutInflater = layoutInflater;
            mData = new SortedList<Item>(Item.class, new SortedListAdapterCallback<Item>(this) {
                @Override
                public int compare(Item t0, Item t1) {
                    if (t0.mIsDone != t1.mIsDone) {
                        return t0.mIsDone ? 1 : -1;
                    }
                    int txtComp = t0.mText.compareTo(t1.mText);
                    if (txtComp != 0) {
                        return txtComp;
                    }
                    if (t0.id < t1.id) {
                        return -1;
                    } else if (t0.id > t1.id) {
                        return 1;
                    }
                    return 0;
                }

                @Override
                public boolean areContentsTheSame(Item oldItem,
                        Item newItem) {
                    return oldItem.mText.equals(newItem.mText);
                }

                @Override
                public boolean areItemsTheSame(Item item1, Item item2) {
                    return item1.id == item2.id;
                }
            });
            for (Item item : items) {
                mData.add(item);
            }
        }

        public void addItem(Item item) {
            mData.add(item);
        }

        @Override
        public TodoViewHolder onCreateViewHolder(final ViewGroup parent, int viewType) {
            return new TodoViewHolder (
                    mLayoutInflater.inflate(R.layout.sorted_list_item_view, parent, false)) {
                @Override
                void onDoneChanged(boolean isDone) {
                    int adapterPosition = getAdapterPosition();
                    if (adapterPosition == RecyclerView.NO_POSITION) {
                        return;
                    }
                    mBoundItem.mIsDone = isDone;
                    mData.recalculatePositionOfItemAt(adapterPosition);
                }
            };
        }

        @Override
        public void onBindViewHolder(TodoViewHolder holder, int position) {
            holder.bindTo(mData.get(position));
        }

        @Override
        public int getItemCount() {
            return mData.size();
        }
    }

    abstract private static class TodoViewHolder extends RecyclerView.ViewHolder {
        final CheckBox mCheckBox;
        Item mBoundItem;
        public TodoViewHolder(View itemView) {
            super(itemView);
            mCheckBox = (CheckBox) itemView;
            mCheckBox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
                @Override
                public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
                    if (mBoundItem != null && isChecked != mBoundItem.mIsDone) {
                        onDoneChanged(isChecked);
                    }
                }
            });
        }

        public void bindTo(Item item) {
            mBoundItem = item;
            mCheckBox.setText(item.mText);
            mCheckBox.setChecked(item.mIsDone);
        }

        abstract void onDoneChanged(boolean isChecked);
    }

    private static class Item {
        String mText;
        boolean mIsDone = false;
        final public int id;
        private static int idCounter = 0;

        public Item(String text) {
            id = idCounter ++;
            this.mText = text;
        }
    }
}

There is a sample SortedListActivity in the support library source repository which demonstrates how to use SortedList and SortedListAdapterCallback inside a RecyclerView.Adapter. From the root of the SDK, with the support library installed, it should be at extras/android/support/samples/Support7Demos/src/com/example/android/supportv7/util/SortedListActivity.java (also on github).

The existence of these particular samples is mentioned exactly once in Google's documentation, at the bottom of a page dealing with a different topic, so I don't blame you for not finding it.

What is the SortedList<T> working with RecyclerView.Adapter?

Sample

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