DiffCallBack.java

package com.mcxtzhang.diffutilsdemo;

import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v7.util.DiffUtil;
import android.support.v7.widget.RecyclerView;

import java.util.List;

/**
 * 介绍：核心类 用来判断 新旧Item是否相等
 * 作者：zhangxutong
 * 邮箱：zhangxutong@imcoming.com
 * 时间： 2016/9/12.
 */

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

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

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

    @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());
    }

    @Override
    public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
        TestBean beanOld = mOldDatas.get(oldItemPosition);
        TestBean beanNew = mNewDatas.get(newItemPosition);
        return beanOld.getDesc().equals(beanNew.getDesc());
    }

    /**
     * 实现这个方法 就能成为文艺青年中的文艺青年
     * 定向刷新中的部分更新
     * 效率最高
     *
     * @param oldItemPosition
     * @param newItemPosition
     * @return
     */
    /**
     * When {@link #areItemsTheSame(int, int)} returns {@code true} for two items and
     * {@link #areContentsTheSame(int, int)} returns false for them, DiffUtil
     * calls this method to get a payload about the change.
     * <p>
     * 当{@link #areItemsTheSame(int, int)} 返回true，且{@link #areContentsTheSame(int, int)} 返回false时，DiffUtils会回调此方法，
     * 去得到这个Item（有哪些）改变的payload。
     * <p>
     * For example, if you are using DiffUtil with {@link RecyclerView}, you can return the
     * particular field that changed in the item and your
     * {@link android.support.v7.widget.RecyclerView.ItemAnimator ItemAnimator} can use that
     * information to run the correct animation.
     * <p>
     * 例如，如果你用RecyclerView配合DiffUtils，你可以返回  这个Item改变的那些字段，
     * {@link android.support.v7.widget.RecyclerView.ItemAnimator ItemAnimator} 可以用那些信息去执行正确的动画
     * <p>
     * Default implementation returns {@code null}.\
     * 默认的实现是返回null
     *
     * @param oldItemPosition The position of the item in the old list
     * @param newItemPosition The position of the item in the new list
     * @return A payload object that represents the change between the two items.
     * 返回 一个 代表着新老item的改变内容的 payload对象，
     */
    @Nullable
    @Override
    public Object getChangePayload(int oldItemPosition, int newItemPosition) {
        TestBean oldBean = mOldDatas.get(oldItemPosition);
        TestBean newBean = mNewDatas.get(newItemPosition);

        //这里就不用比较核心字段了,一定相等
        Bundle payload = new Bundle();
        if (!oldBean.getDesc().equals(newBean.getDesc())) {
            payload.putString("KEY_DESC", newBean.getDesc());
        }
        if (oldBean.getPic() != newBean.getPic()) {
            payload.putInt("KEY_PIC", newBean.getPic());
        }

        if (payload.size() == 0)//如果没有变化 就传空
            return null;
        return payload;
    }
}