Android7.0 工具类：DiffUtil详解

class TestBean implements Cloneable {
 private String name;
 private String desc;
 ....//get set方法省略
 //仅写DEMO 用 实现克隆方法
 @Override
 public TestBean clone() throws CloneNotSupportedException {
  TestBean bean = null;
  try {
   bean = (TestBean) super.clone();
  } catch (CloneNotSupportedException e) {
   e.printStackTrace();
  }
  return bean;
 }

public class DiffAdapter extends RecyclerView.Adapter<DiffAdapter.DiffVH> {
 private final static String TAG = "zxt";
 private List<TestBean> mDatas;
 private Context mContext;
 private LayoutInflater mInflater;

 public DiffAdapter(Context mContext, List<TestBean> mDatas) {
  this.mContext = mContext;
  this.mDatas = mDatas;
  mInflater = LayoutInflater.from(mContext);
 }

 public void setDatas(List<TestBean> mDatas) {
  this.mDatas = mDatas;
 }

 @Override
 public DiffVH onCreateViewHolder(ViewGroup parent, int viewType) {
  return new DiffVH(mInflater.inflate(R.layout.item_diff, parent, false));
 }

 @Override
 public void onBindViewHolder(final DiffVH holder, final int position) {
  TestBean bean = mDatas.get(position);
  holder.tv1.setText(bean.getName());
  holder.tv2.setText(bean.getDesc());
  holder.iv.setImageResource(bean.getPic());
 }

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

 class DiffVH extends RecyclerView.ViewHolder {
  TextView tv1, tv2;
  ImageView iv;

  public DiffVH(View itemView) {
   super(itemView);
   tv1 = (TextView) itemView.findViewById(R.id.tv1);
   tv2 = (TextView) itemView.findViewById(R.id.tv2);
   iv = (ImageView) itemView.findViewById(R.id.iv);
  }
 }
}

public class MainActivity extends AppCompatActivity {
 private List<TestBean> mDatas;
 private RecyclerView mRv;
 private DiffAdapter mAdapter;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  initData();
  mRv = (RecyclerView) findViewById(R.id.rv);
  mRv.setLayoutManager(new LinearLayoutManager(this));
  mAdapter = new DiffAdapter(this, mDatas);
  mRv.setAdapter(mAdapter);
 }

 private void initData() {
  mDatas = new ArrayList<>();
  mDatas.add(new TestBean("张旭童1", "Android", R.drawable.pic1));
  mDatas.add(new TestBean("张旭童2", "Java", R.drawable.pic2));
  mDatas.add(new TestBean("张旭童3", "背锅", R.drawable.pic3));
  mDatas.add(new TestBean("张旭童4", "手撕产品", R.drawable.pic4));
  mDatas.add(new TestBean("张旭童5", "手撕测试", R.drawable.pic5));
 }

 /**
  * 模拟刷新操作
  *
  * @param view
  */
 public void onRefresh(View view) {
  try {
   List<TestBean> newDatas = new ArrayList<>();
   for (TestBean bean : mDatas) {
    newDatas.add(bean.clone());//clone一遍旧数据 ，模拟刷新操作
   }
   newDatas.add(new TestBean("赵子龙", "帅", R.drawable.pic6));//模拟新增数据
   newDatas.get(0).setDesc("Android+");
   newDatas.get(0).setPic(R.drawable.pic7);//模拟修改数据
   TestBean testBean = newDatas.get(1);//模拟数据位移
   newDatas.remove(testBean);
   newDatas.add(testBean);
   //别忘了将新数据给Adapter
   mDatas = newDatas;
   mAdapter.setDatas(mDatas);
   mAdapter.notifyDataSetChanged();//以前我们大多数情况下只能这样
  } catch (CloneNotSupportedException e) {
   e.printStackTrace();
  }
 }

}

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
>

 <android.support.v7.widget.RecyclerView
  android:id="@+id/rv" />

 <Button
  android:id="@+id/btnRefresh"
  android:layout_alignParentRight="true"
  android:onClick="onRefresh"
  android:text="模拟刷新" />
</RelativeLayout>

 public abstract static class Callback {
  public abstract int getOldListSize();//老数据集size

  public abstract int getNewListSize();//新数据集size

  public abstract boolean areItemsTheSame(int oldItemPosition, int newItemPosition);//新老数据集在同一个postion的Item是否是一个对象？（可能内容不同，如果这里返回true，会调用下面的方法）

  public abstract boolean areContentsTheSame(int oldItemPosition, int newItemPosition);//这个方法仅仅是上面方法返回ture才会调用，我的理解是只有notifyItemRangeChanged()才会调用，判断item的内容是否有变化

  //该方法在DiffUtil高级用法中用到 ，暂且不提
  @Nullable
  public Object getChangePayload(int oldItemPosition, int newItemPosition) {
   return null;
  }
 }

/**
 * 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;//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);

 public void dispatchUpdatesTo(final RecyclerView.Adapter adapter) {
   dispatchUpdatesTo(new ListUpdateCallback() {
    @Override
    public void onInserted(int position, int count) {
     adapter.notifyItemRangeInserted(position, count);
    }

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

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

    @Override
    public void onChanged(int position, int count, Object payload) {
     adapter.notifyItemRangeChanged(position, count, payload);
    }
   });
  }

 /**
   * Called by RecyclerView to display the data at the specified position. This method
   * should update the contents of the {@link ViewHolder#itemView} to reflect the item at
   * the given position.
   * <p>
   * Note that unlike {@link android.widget.ListView}, RecyclerView will not call this method
   * again if the position of the item changes in the data set unless the item itself is
   * invalidated or the new position cannot be determined. For this reason, you should only
   * use the <code>position</code> parameter while acquiring the related data item inside
   * this method and should not keep a copy of it. If you need the position of an item later
   * on (e.g. in a click listener), use {@link ViewHolder#getAdapterPosition()} which will
   * have the updated adapter position.
   * <p>
   * Partial bind vs full bind:
   * <p>
   * The payloads parameter is a merge list from {@link #notifyItemChanged(int, Object)} or
   * {@link #notifyItemRangeChanged(int, int, Object)}. If the payloads list is not empty,
   * the ViewHolder is currently bound to old data and Adapter may run an efficient partial
   * update using the payload info. If the payload is empty, Adapter must run a full bind.
   * Adapter should not assume that the payload passed in notify methods will be received by
   * onBindViewHolder(). For example when the view is not attached to the screen, the
   * payload in notifyItemChange() will be simply dropped.
   *
   * @param holder The ViewHolder which should be updated to represent the contents of the
   *    item at the given position in the data set.
   * @param position The position of the item within the adapter‘s data set.
   * @param payloads A non-null list of merged payloads. Can be empty list if requires full
   *     update.
   */
  public void onBindViewHolder(VH holder, int position, List<Object> payloads) {
   onBindViewHolder(holder, position);
  }

 /**
  * 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.
  * 
  * 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。
  * 
  * 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.
  * 
  * 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
  * 
  * 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) {
  //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
  //只是没有了ItemChange的白光一闪动画，（反正我也觉得不太重要）
  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;//
 }

 @Override
 public void onBindViewHolder(DiffVH holder, int position, List<Object> payloads) {
  if (payloads.isEmpty()) {
   onBindViewHolder(holder, position);
  } else {
   //文艺青年中的文青
   Bundle payload = (Bundle) payloads.get(0);
   TestBean bean = mDatas.get(position);
   for (String key : payload.keySet()) {
    switch (key) {
     case "KEY_DESC":
      //这里可以用payload里的数据，不过data也是新的 也可以用
      holder.tv2.setText(bean.getDesc());
      break;
     case "KEY_PIC":
      holder.iv.setImageResource(payload.getInt(key));
      break;
     default:
      break;
    }
   }
  }
 }

 private static final int H_CODE_UPDATE = 1;
 private List<TestBean> mNewDatas;//增加一个变量暂存newList
 private Handler mHandler = new Handler() {
  @Override
  public void handleMessage(Message msg) {
   switch (msg.what) {
    case H_CODE_UPDATE:
     //取出Result
     DiffUtil.DiffResult diffResult = (DiffUtil.DiffResult) msg.obj;
     diffResult.dispatchUpdatesTo(mAdapter);
     //别忘了将新数据给Adapter
     mDatas = mNewDatas;
     mAdapter.setDatas(mDatas);
     break;
   }
  }
 };
   new Thread(new Runnable() {
    @Override
    public void run() {
     //放在子线程中计算DiffResult
     DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new DiffCallBack(mDatas, mNewDatas), true);
     Message message = mHandler.obtainMessage(H_CODE_UPDATE);
     message.obj = diffResult;//obj存放DiffResult
     message.sendToTarget();
    }
   }).start();