DiffUtil使用代码

1 DiffUtil

public class DiffCallBack extends DiffUtil.Callback {
    private List<TestBean> mOldDatas, mNewDatas;//看名字

    public DiffCallBack(List<TestBean> mOldDatas, List<TestBean> mNewDatas) {
        this.mOldDatas = mOldDatas;
        this.mNewDatas = mNewDatas;
    }

    //老数据集size
    @Override
    public int getOldListSize() {
        return mOldDatas != null ? mOldDatas.size() : 0;
    }

    //新数据集size
    @Override
    public int getNewListSize() {
        return mNewDatas != null ? mNewDatas.size() : 0;
    }

    /**
     * Called by the DiffUtil to decide whether two object represent the same Item.
     * 被DiffUtil调用，用来判断 两个对象是否是相同的Item。
     * For example, if your items have unique ids, this method should check their id equality.
     * 例如，如果你的Item有唯一的id字段，这个方法就 判断id是否相等。
     * 本例判断name字段是否一致
     *
     * @param oldItemPosition The position of the item in the old list
     * @param newItemPosition The position of the item in the new list
     * @return True if the two items represent the same object or false if they are different.
     */
    @Override
    public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
        return mOldDatas.get(oldItemPosition).getName().equals(mNewDatas.get(newItemPosition).getName());
    }

    /**
     * Called by the DiffUtil when it wants to check whether two items have the same data.
     * 被DiffUtil调用，用来检查 两个item是否含有相同的数据
     * DiffUtil uses this information to detect if the contents of an item has changed.
     * DiffUtil用返回的信息（true false）来检测当前item的内容是否发生了变化
     * DiffUtil uses this method to check equality instead of {@link Object#equals(Object)}
     * DiffUtil 用这个方法替代equals方法去检查是否相等。
     * so that you can change its behavior depending on your UI.
     * 所以你可以根据你的UI去改变它的返回值
     * For example, if you are using DiffUtil with a
     * {@link android.support.v7.widget.RecyclerView.Adapter RecyclerView.Adapter}, you should
     * return whether the items' visual representations are the same.
     * 例如，如果你用RecyclerView.Adapter 配合DiffUtil使用，你需要返回Item的视觉表现是否相同。
     * This method is called only if {@link #areItemsTheSame(int, int)} returns
     * {@code true} for these items.
     * 这个方法仅仅在areItemsTheSame()返回true时，才调用。
     * @param oldItemPosition The position of the item in the old list
     * @param newItemPosition The position of the item in the new list which replaces the
     *                        oldItem
     * @return True if the contents of the items are the same or false if they are different.
     */
    @Override
    public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
        TestBean beanOld = mOldDatas.get(oldItemPosition);
        TestBean beanNew = mNewDatas.get(newItemPosition);
        if (!beanOld.getDesc().equals(beanNew.getDesc())) {
            return false;//如果有内容不同，就返回false
        }
        if (beanOld.getPic() != beanNew.getPic()) {
            return false;//如果有内容不同，就返回false
        }
        return true; //默认两个data内容是相同的
    }

//文艺青年新宠
//利用DiffUtil.calculateDiff()方法，传入一个规则DiffUtil.Callback对象，和是否检测移动item的 boolean变量，得到DiffUtil.DiffResult 的对象

DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new DiffCallBack(mDatas, newDatas), true);

//利用DiffUtil.DiffResult对象的dispatchUpdatesTo（）方法，传入RecyclerView的Adapter，轻松成为文艺青年

diffResult.dispatchUpdatesTo(mAdapter);

//别忘了将新数据给Adapter
mDatas = newDatas;
mAdapter.setDatas(mDatas);

2 AsyncListDiffer

public class UserAdapter extends RecyclerView.Adapter<UserAdapter.UserViewHodler> {
    private AsyncListDiffer<User> mDiffer;

    private DiffUtil.ItemCallback<User> diffCallback = new DiffUtil.ItemCallback<User>() {
        @Override
        public boolean areItemsTheSame(User oldItem, User newItem) {
            return TextUtils.equals(oldItem.getId(), newItem.getId());
        }

        @Override
        public boolean areContentsTheSame(User oldItem, User newItem) {
            return oldItem.getAge() == newItem.getAge();
        }
    };

    public UserAdapter() {
        mDiffer = new AsyncListDiffer<>(this, diffCallback);
    }

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

    public void submitList(List<User> data) {
        mDiffer.submitList(data);
    }

    public User getItem(int position) {
        return mDiffer.getCurrentList().get(position);
    }

    @NonNull
    @Override
    public UserAdapter.UserViewHodler onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_user_list, parent, false);
        return new UserViewHodler(itemView);
    }

    @Override
    public void onBindViewHolder(@NonNull UserAdapter.UserViewHodler holder, int position) {
        holder.setData(getItem(position));
    }

    class UserViewHodler extends RecyclerView.ViewHolder {
        private TextView tvName;
        private TextView tvAge;

        public UserViewHodler(View itemView) {
            super(itemView);
            tvName = itemView.findViewById(R.id.tv_name);
            tvAge = itemView.findViewById(R.id.tv_age);
        }

        public void setData(User data) {
            tvName.setText(data.getName());
            tvAge.setText(String.valueOf(data.getAge()));
        }
    }
}