DiffRecyclerViewBindingAdapter.java

/*
 * Copyright 2016 "Henry Tao <hi@henrytao.me>"
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package me.henrytao.shopifyblogandroid.util;

import android.support.annotation.NonNull;
import android.support.v7.util.DiffUtil;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

import me.henrytao.mvvmlifecycle.MVVMObserver;
import me.henrytao.mvvmlifecycle.recyclerview.RecyclerViewBindingAdapter;
import me.henrytao.mvvmlifecycle.recyclerview.RecyclerViewBindingViewHolder;
import me.henrytao.mvvmlifecycle.rx.SubscriptionUtils;
import me.henrytao.mvvmlifecycle.rx.Transformer;
import rx.Observable;

/**
 * Created by henrytao on 9/29/16.
 */
public class DiffRecyclerViewBindingAdapter<D, V extends RecyclerViewBindingViewHolder<D>> extends RecyclerViewBindingAdapter<D, V> {

  private final DataComparable<D> mComparable;

  private final List<D> mShadowData;

  public DiffRecyclerViewBindingAdapter(Class<V> clsView, MVVMObserver observer, @NonNull List<D> shadowData,
      DataComparable<D> comparable) {
    super(clsView, observer, new ArrayList<>());
    mShadowData = shadowData;
    mComparable = comparable;
  }

  public void applyDiff() {
    applyDiff(true);
  }

  public Observable<Void> calculateDiff() {
    Observable<DiffUtil.DiffResult> observable = Observable.create(subscriber -> {
      try {
        DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new DiffUtilCallback<>(mComparable, mData, mShadowData));
        SubscriptionUtils.onNextAndComplete(subscriber, diffResult);
      } catch (Exception exception) {
        SubscriptionUtils.onError(subscriber, exception);
      }
    });
    return observable.flatMap(this::applyDiff).map(o -> null);
  }

  private void applyDiff(boolean shouldNotifyDataSetChanged) {
    mData.clear();
    mData.addAll(mShadowData);
    if (shouldNotifyDataSetChanged) {
      notifyDataSetChanged();
    }
  }

  private Observable<Void> applyDiff(DiffUtil.DiffResult diffResult) {
    Observable<Void> observable = Observable.create(subscriber -> {
      applyDiff(false);
      diffResult.dispatchUpdatesTo(this);
      SubscriptionUtils.onComplete(subscriber);
    });
    return observable.compose(Transformer.applyMainThreadScheduler());
  }

  public interface DataComparable<D> extends ItemComparable<D> {

    boolean areContentsTheSame(D oldData, D newData);
  }

  public interface ItemComparable<D> {

    boolean areItemsTheSame(D oldData, D newData);
  }

  public static class DiffArrayList<D> extends ArrayList<D> {

    private final ItemComparable<D> mComparable;

    public DiffArrayList(@NonNull ItemComparable<D> comparable, int capacity) {
      super(capacity);
      mComparable = comparable;
    }

    public DiffArrayList(@NonNull ItemComparable<D> comparable) {
      mComparable = comparable;
    }

    public DiffArrayList(@NonNull ItemComparable<D> comparable, Collection<? extends D> collection) {
      super(collection);
      mComparable = comparable;
    }

    @Override
    public boolean add(D object) {
      int existedIndex = indexOfWithComparable(object);
      if (existedIndex >= 0) {
        set(existedIndex, object);
        return true;
      }
      return super.add(object);
    }

    @Override
    public void add(int index, D object) {
      int existedIndex = indexOfWithComparable(object);
      if (existedIndex >= 0) {
        set(existedIndex, object);
      } else {
        super.add(index, object);
      }
    }

    @SuppressWarnings("unchecked")
    @Override
    public boolean addAll(Collection<? extends D> collection) {
      Object[] newPart = collection.toArray();
      for (Object object : newPart) {
        add((D) object);
      }
      return true;
    }

    @SuppressWarnings("unchecked")
    @Override
    public boolean addAll(int index, Collection<? extends D> collection) {
      Object[] newPart = collection.toArray();
      int i = newPart.length - 1;
      while (i >= 0) {
        add(index, (D) newPart[i]);
        i--;
      }
      return true;
    }

    @SuppressWarnings("unchecked")
    @Override
    public boolean remove(Object object) {
      try {
        int index = indexOfWithComparable((D) object);
        if (index >= 0) {
          remove(index);
        }
      } catch (ClassCastException ignore) {
        return false;
      }
      return true;
    }

    private int indexOfWithComparable(D object) {
      int size = size();
      for (int i = 0; i < size; i++) {
        if (mComparable.areItemsTheSame(object, get(i))) {
          return i;
        }
      }
      return -1;
    }
  }

  private static class DiffUtilCallback<D> extends DiffUtil.Callback {

    private final DataComparable<D> mDataComparable;

    private final List<D> mNewData;

    private final List<D> mOldData;

    private DiffUtilCallback(DataComparable<D> dataComparable, List<D> oldData, List<D> newData) {
      mOldData = oldData;
      mNewData = newData;
      mDataComparable = dataComparable;
    }

    @Override
    public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
      return mDataComparable.areContentsTheSame(mOldData.get(oldItemPosition), mNewData.get(newItemPosition));
    }

    @Override
    public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
      return mDataComparable.areItemsTheSame(mOldData.get(oldItemPosition), mNewData.get(newItemPosition));
    }

    @Override
    public int getNewListSize() {
      return mNewData.size();
    }

    @Override
    public int getOldListSize() {
      return mOldData.size();
    }
  }
}