在5.0以后大家在使用列表控件時已經(jīng)逐漸的使用recycleView來代替ListView了坑雅，但是很多人并不了解recycleView的高效率的刷新方式

首先我們先介紹一下recycleView自帶的刷新方式：

1.使用 Adapter.notifyDataSetChanged();

優(yōu)點：簡單粗暴直接刷新所有的Item布局

缺點：（1）刷新的太多了影響效率辆童，如果遇到復雜的邏輯容易卡頓
（2）刷新的時候無法觸發(fā) recycleView 的動畫

2.自帶的局部刷新

Adapter.notifyItemChanged(int)

Adapter.notifyItemInserted(int)

Adapter.notifyItemRangeChanged(int,int)

Adapter.notifyItemRangeInserted(int,int)

Adapter.notifyItemRangeRemoved(int,int)

優(yōu)點：不用刷新整個列表可以局部刷新提高效率

缺點：每次刷新都要知道position 如果刷新單條比較好使擔當刷新條目比較多的時候需要單獨計算每個條目的position不是很方便

3.使用DiffUtil android recycleView-24以后自帶的比對數(shù)據(jù)的類

使用方法：
（1）正常創(chuàng)建adapter 注意設(shè)置數(shù)據(jù)是新建一個List 去接受數(shù)據(jù)

public void setData(List<TextModel> data) {
    this.data = new ArrayList<>(data);
}

因為在比較的時候需要oldList與新 newList 比較才能得出變化的數(shù)據(jù)

（2）創(chuàng)建DiffUtil.Callback

public class MyCallback extends DiffUtil.Callback {

  private List<TextModel> old_students, new_students;

  public MyCallback(List<TextModel> data, List<TextModel> students) {
    this.old_students = data;
    this.new_students = students;
  }

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

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

  // 判斷Item是否已經(jīng)存在
  @Override
  public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
    return old_students.get(oldItemPosition).getTextTitle() == new_students.get(newItemPosition).getTextTitle();
  }

// 如果Item已經(jīng)存在則會調(diào)用此方法，判斷Item的內(nèi)容是否一致
  @Override
  public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
    return old_students.get(oldItemPosition).getTextContent().equals(new_students.get(newItemPosition).getTextContent());
  }
}

在這里面需要聲明判斷Item是否已經(jīng)存在條件和如果Item已經(jīng)存在則會調(diào)用此方法幌绍，判斷Item的內(nèi)容是否一致條件。

(3)得到比較結(jié)果重新設(shè)置數(shù)據(jù)

    DiffUtil.DiffResult result = DiffUtil.calculateDiff(new MyCallback(oldList, mTextModels), true);
    myAdapter.setData(mTextModels);
    result.dispatchUpdatesTo(myAdapter);

優(yōu)點：可以自定義比較兩個列表中的數(shù)據(jù)并刷新

缺點：（1）DiffUtil.calculateDiff()這個方法是執(zhí)行在主線程的故响，如果新舊數(shù)據(jù)List比較大傀广，那么這個方法會阻塞主線程可能出現(xiàn)出現(xiàn)ANR
（2）比較完成后必須調(diào)用result.dispatchUpdatesTo(myAdapter)重新設(shè)置數(shù)據(jù)

(4)使用AsyncListDiff android recycleView-27以后自帶的比對數(shù)據(jù)的類
android 在recycleView 的V27包對原來的數(shù)據(jù)比對類進行了更新產(chǎn)生的一個新的數(shù)據(jù)比對類就是 AsyncListDiff

使用方法：

（1）創(chuàng)建adapter并在adapter中自實現(xiàn)DiffUtil.ItemCallback，給出item差異性計算條件

 public class MyItemCallBack extends DiffUtil.ItemCallback<TextModel> {
    @Override
    public boolean areItemsTheSame(@NonNull TextModel oldItem, @NonNull TextModel newItem) {
      return TextUtils.equals(oldItem.getTextTitle(), newItem.getTextTitle());
    }

    @Override
    public boolean areContentsTheSame(@NonNull TextModel oldItem, @NonNull TextModel newItem) {
      return TextUtils.equals(oldItem.getTextContent(), newItem.getTextContent());
    }
}

（2）將所有對數(shù)據(jù)的操作代理給AsyncListDiffer彩届，可以看到這個Adapter是沒有List數(shù)據(jù)的

public class MyDiffAdapter  extends RecyclerView.Adapter {
  private Context mContext;
  private AsyncListDiffer<TextModel> mTextDiffl;
  private DiffUtil.ItemCallback<TextModel> diffCallback = new MyItemCallBack();

  public MyDiffAdapter(Context mContext) {
      this.mContext = mContext;
      mTextDiffl = new AsyncListDiffer<>(this, diffCallback);
  }

  @NonNull
  @Override
  public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
      View itemView = LayoutInflater.from(mContext).inflate(R.layout.item_view, null);
      return new MyViewHolder(itemView);
  }

  @Override
  public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
      MyAdapter.MyViewHolder myViewHolder = (MyAdapter.MyViewHolder) holder;
      TextModel textModel = getItem(position);
      myViewHolder.tv.setText(textModel.getTextTitle() + "." + textModel.getTextContent());
  }

  @Override
  public int getItemCount() {
      return mTextDiffl.getCurrentList().size();
  }
  public void submitList(List<TextModel> data) {
    mTextDiffl.submitList(data);
  }

  public TextModel getItem(int position) {
      return mTextDiffl.getCurrentList().get(position);
  }

  class MyViewHolder extends RecyclerView.ViewHolder {
      TextView tv;

      MyViewHolder(View itemView) {
          super(itemView);
          tv = (TextView) itemView.findViewById(R.id.item_tv);
    }
  }
}

（3）使用submitList()更新數(shù)據(jù)伪冰，并刷新ui

public void change1() {
    for(int i = 0; i<10;i++){
        TextModel textModel= new TextModel("aa"+i,"bb"+i%3);
        mTextModels.add(textModel);
    }
    myDiffAdapter.submitList(mTextModels);
}

對比之前DiffUtil 優(yōu)點：（1）不用創(chuàng)來那個兩個List比較
（2）將比較放在了子線程中不再中主線程中比較減少刷新造成的卡頓
下面解析一下 AsyncListDiffer的源碼

public class AsyncListDiffer<T> {
  private final ListUpdateCallback mUpdateCallback;
  final AsyncDifferConfig<T> mConfig;
  final Executor mMainThreadExecutor;
  private static final Executor sMainThreadExecutor = new AsyncListDiffer.MainThreadExecutor();
  @Nullable
  private List<T> mList;
  @NonNull
  private List<T> mReadOnlyList;
  int mMaxScheduledGeneration;

  public AsyncListDiffer(@NonNull Adapter adapter, @NonNull ItemCallback<T> diffCallback) {
      this((ListUpdateCallback)(new AdapterListUpdateCallback(adapter)), (AsyncDifferConfig)(new Builder(diffCallback)).build());
  }

  public AsyncListDiffer(@NonNull ListUpdateCallback listUpdateCallback, @NonNull AsyncDifferConfig<T> config) {
      this.mReadOnlyList = Collections.emptyList();
      this.mUpdateCallback = listUpdateCallback;
      this.mConfig = config;
      if (config.getMainThreadExecutor() != null) {
          this.mMainThreadExecutor = config.getMainThreadExecutor();
      } else {
          this.mMainThreadExecutor = sMainThreadExecutor;
      }

  }

  @NonNull
  public List<T> getCurrentList() {
      return this.mReadOnlyList;
  }

  public void submitList(@Nullable final List<T> newList) {
      // 用于控制計算線程，防止在上一次submitList未完成時樟蠕，
      // 又多次調(diào)用submitList贮聂，這里只返回最后一個計算的DiffResult
      final int runGeneration = ++this.mMaxScheduledGeneration;
      if (newList != this.mList) {
          if (newList == null) {
              int countRemoved = this.mList.size();
              this.mList = null;
              this.mReadOnlyList = Collections.emptyList();
              this.mUpdateCallback.onRemoved(0, countRemoved);
          } else if (this.mList == null) {
              this.mList = newList;
              this.mReadOnlyList = Collections.unmodifiableList(newList);
              this.mUpdateCallback.onInserted(0, newList.size());
          } else {
              final List<T> oldList = this.mList;
              this.mConfig.getBackgroundThreadExecutor().execute(new Runnable() {
                  public void run() {
                      final DiffResult result = DiffUtil.calculateDiff(new Callback() {
                          public int getOldListSize() {
                              return oldList.size();
                          }

                          public int getNewListSize() {
                              return newList.size();
                          }

                          public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
                              T oldItem = oldList.get(oldItemPosition);
                              T newItem = newList.get(newItemPosition);
                              if (oldItem != null && newItem != null) {
                                  return AsyncListDiffer.this.mConfig.getDiffCallback().areItemsTheSame(oldItem, newItem);
                              } else {
                                  return oldItem == null && newItem == null;
                              }
                        }

                          public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
                              T oldItem = oldList.get(oldItemPosition);
                              T newItem = newList.get(newItemPosition);
                              if (oldItem != null && newItem != null) {
                                  return AsyncListDiffer.this.mConfig.getDiffCallback().areContentsTheSame(oldItem, newItem);
                              } else if (oldItem == null && newItem == null) {
                                  return true;
                              } else {
                                  throw new AssertionError();
                              }
                          }

                          @Nullable
                          public Object getChangePayload(int oldItemPosition, int newItemPosition) {
                              T oldItem = oldList.get(oldItemPosition);
                              T newItem = newList.get(newItemPosition);
                              if (oldItem != null && newItem != null) {
                                  return AsyncListDiffer.this.mConfig.getDiffCallback().getChangePayload(oldItem, newItem);
                              } else {
                                  throw new AssertionError();
                              }
                          }
                      });
                      AsyncListDiffer.this.mMainThreadExecutor.execute(new Runnable() {
                          public void run() {
                              if (AsyncListDiffer.this.mMaxScheduledGeneration == runGeneration) {
                                 AsyncListDiffer.this.latchList(newList, result);
                              }

                          }
                      });
                  }
              });
          }
      }
  }

  void latchList(@NonNull List<T> newList, @NonNull DiffResult diffResult) {
      this.mList = newList;
      this.mReadOnlyList = Collections.unmodifiableList(newList);
      diffResult.dispatchUpdatesTo(this.mUpdateCallback);
  }

  private static class MainThreadExecutor implements Executor {
      final Handler mHandler = new Handler(Looper.getMainLooper());

      MainThreadExecutor() {
      }

      public void execute(@NonNull Runnable command) {
          this.mHandler.post(command);
      }
  }
}

他其實就是google自己對DiffUtil進行的一次封裝
（1）首先在構(gòu)造方法中創(chuàng)建線程池進行管理
（2）submitList時候先判斷數(shù)組的內(nèi)存地址是否相同
（3）判空
（4）開啟子線程使用DiffUtil.calculateDiff進行數(shù)據(jù)比較
（5）回調(diào)

demo github地址：https://github.com/525642022/localRefresh

android RecycleView 局部刷新方式總結(jié)

android RecycleView 局部刷新方式總結(jié)

1.使用 Adapter.notifyDataSetChanged();

2.自帶的局部刷新

3.使用DiffUtil android recycleView-24以后自帶的比對數(shù)據(jù)的類