java - 我的DiffUtil实现有什么问题？

更新:解决了一个问题:现在解决了updateList，问题是我将mAdapter定义为RecyclerView.Adapter而不是MyAdapter。但是现在即使我正在获取数据，列表上也没有任何显示，它是空的

-------------------- 原始帖子 --------------------

我想使用RecyclerView更新DiffUtil以防止重复。

我有4个类:用户类，设置数据的Activity类，Adapter类和DiffUtil类。我不确定我是否正确组合了所有这四个。

这是User类:

public class User {

    private String mUserId;
    private Uri mImageUrl;


    public User(String userId, String imageUrl) {
        mUserId = userId;
        mImageUrl = Uri.parse(imageUrl);
    }


    public String getUserId() {
        return mUserId;
    }

    public Uri getImageUrl() {
        return mImageUrl;
    }
}

这就是我动态设置数据的方式(我不断从服务器上获取要显示的包含用户ID的新Json数组，然后从Firebase存储中设置用户图像):(这是一个由onClick监听器调用的函数:)

这是 fragment 中的方法调用:

button.setOnClickListener(new View.OnClickListener() {
    public void onClick(View v) {
        updateUsersList();
    }
});

这是功能:

   private void updateUsersList() {
        @Override
        public void onResponse(JSONArray response) { // the JSON ARRAY response of user ids ["uid1", "uid334", "uid1123"]
            myDataset.clear(); // clear dataset to prevent duplicates
            for (int i = 0; i < response.length(); i++) {
                try {
                    String userKey = response.get(i).toString(); // the currently iterated user id
                    final DatabaseReference rootRef = FirebaseDatabase.getInstance().getReference();
                    DatabaseReference userKeyRef = rootRef.child("users").child(userKey); // reference to currently iterated user
                    ValueEventListener listener = new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        myDataset.add(new User(dataSnapshot.getKey(), dataSnapshot.child("imageUrl").getValue().toString())); //add new user: id and image url
                        mAdapter.updateList(myDataset); // cannot resolve this method, why?
                   }
                   @Override
                   public void onCancelled(@NonNull DatabaseError databaseError) {
                   Log.d(TAG, databaseError.getMessage());
                   }
                  };
                  userKeyRef.addListenerForSingleValueEvent(listener);
              }
              catch (JSONException e) { Log.d(TAG, "message " + e); }
           }
   }

这是我的DiffUtil类的样子:

public class MyDiffUtilCallBack extends DiffUtil.Callback{

    ArrayList<User> oldUsers;
    ArrayList<User> newUsers;

    public MyDiffUtilCallBack(ArrayList<User> newUsers, ArrayList<User> oldUsers) {
        this.newUsers = newUsers;
        this.oldUsers = oldUsers;
    }

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

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

    @Override
    public boolean areItemsTheSame(int oldItemPosition, int newItemPosition) {
        return oldUsers.get(oldItemPosition).getUserId().equals( newUsers.get(newItemPosition).getUserId());
    }

    @Override
    public boolean areContentsTheSame(int oldItemPosition, int newItemPosition) {
        return oldUsers.get(oldItemPosition).equals(newUsers.get(newItemPosition));
    }

    @Nullable
    @Override
    public Object getChangePayload(int oldItemPosition, int newItemPosition) {
        //you can return particular field for changed item.
        return super.getChangePayload(oldItemPosition, newItemPosition);
    }
}

这是我的适配器:

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    private ArrayList<User> mDataset;
    private MyViewHolder myHolder;
    private User user;

    public static class MyViewHolder extends RecyclerView.ViewHolder {

        public TextView singleItemTextView;
        public ImageView singleItemImage;
        public View layout;
        public ConstraintLayout constraintLayout;
        public MyViewHolder(View v) {
            super(v);
            layout = v;
            singleItemImage = (ImageView) v.findViewById(R.id.icon);
            singleItemTextView = (TextView) v.findViewById(R.id.singleitemtv);
            constraintLayout = (ConstraintLayout) v.findViewById(R.id.nbConstraintLayout);
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter(ArrayList<User> myDataset) {
        mDataset = myDataset;
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent,
                                                     int viewType) {


        View v =  LayoutInflater.from(parent.getContext())
                .inflate(R.layout.nb_image_view, parent, false);

        MyViewHolder vh = new MyViewHolder(v);
        return vh;
    }

    @Override
    public void onBindViewHolder(final MyViewHolder holder, final int position) {
        myHolder = holder;


        user = mDataset.get(position);
        Uri userImage = user.getImageUrl();
        myHolder.singleItemTextView.setText(user.getUserId());

        Glide.with(myHolder.itemView.getContext() /* context */)
                .load(userImage)
                .into(myHolder.singleItemImage);
        myHolder.constraintLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                 Context context = v.getContext();
                Intent intent = new Intent(v.getContext(), DisplayUserActivity.class);
              context.startActivity(intent);
            }
        });

    }
    public void updateList(ArrayList<User> newList) {
        DiffUtil.DiffResult diffResult = DiffUtil.calculateDiff(new MyDiffUtilCallBack(this.mDataset, newList));
        diffResult.dispatchUpdatesTo(this);
    }
}

我不确定我是否正确组合了所有类(我第一次使用DiffUtil)，我也得到了cannot resolve method updateList(?)
我究竟做错了什么？

这是我在Fragment中定义mAdapter的方式:

public class MyFragment extends Fragment {
    private ArrayList<User> myDataset;
    private RecyclerView.Adapter mAdapter;

    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment
        rootView = inflater.inflate(R.layout.fragment_lks, container, false);

        mRecyclerView = (RecyclerView) rootView.findViewById(R.id.my_recycler_view);
        myDataset = new ArrayList<User>();
        mAdapter = new MyAdapter(myDataset);

最佳答案

问题来自mAdapter的定义。您将其定义为RecyclerView.Adapter，它是MyAdapter的父类(super class)，并且不包含updateList()。您应该将其更改为以下内容:

private MyAdapter mAdapter;

更新于1/13/2019:
我已经使用AsyncListDiffer修改了您的适配器，它会异步计算差异，然后将其应用于适配器。
MyAdapter.java

import android.content.Context;
import android.content.Intent;
import android.net.Uri;
import android.support.annotation.NonNull;
import android.support.constraint.ConstraintLayout;
import android.support.v7.recyclerview.extensions.AsyncListDiffer;
import android.support.v7.util.DiffUtil;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import com.bumptech.glide.Glide;
import java.util.List;


public class MyAdapter extends RecyclerView.Adapter<MyAdapter.MyViewHolder> {

    private AsyncListDiffer<User> mAsyncListDiffer;

    public static class MyViewHolder extends RecyclerView.ViewHolder {

        public TextView singleItemTextView;
        public ImageView singleItemImage;
        public View layout;
        public ConstraintLayout constraintLayout;

        public MyViewHolder(View v) {
            super(v);
            layout = v;
            singleItemImage = (ImageView) v.findViewById(R.id.icon);
            singleItemTextView = (TextView) v.findViewById(R.id.singleitemtv);
            constraintLayout = (ConstraintLayout) v.findViewById(R.id.nbConstraintLayout);
        }
    }

    // Provide a suitable constructor (depends on the kind of dataset)
    public MyAdapter() {
        DiffUtil.ItemCallback<User> diffUtilCallback = new DiffUtil.ItemCallback<User>() {

            @Override
            public boolean areItemsTheSame(@NonNull User newUser, @NonNull User oldUser) {
                return newUser.getUserId().equals(oldUser.getUserId());
            }

            @Override
            public boolean areContentsTheSame(@NonNull User newUser, @NonNull User oldUser) {
                return newUser.equals(oldUser);
            }
        };
        mAsyncListDiffer = new AsyncListDiffer<>(this, diffUtilCallback);
    }

    // Create new views (invoked by the layout manager)
    @Override
    public MyAdapter.MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.nb_image_view, parent, false);
        MyViewHolder vh = new MyViewHolder(v);
        return vh;
    }

    @Override
    public void onBindViewHolder(final MyViewHolder holder, final int position) {
        User user = mAsyncListDiffer.getCurrentList().get(position);
        Uri userImage = user.getImageUrl();
        holder.singleItemTextView.setText(user.getUserId());

        Glide.with(holder.itemView.getContext() /* context */)
                .load(userImage)
                .into(holder.singleItemImage);

        holder.constraintLayout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Context context = v.getContext();
                Intent intent = new Intent(v.getContext(), DisplayUserActivity.class);
                context.startActivity(intent);
            }
        });
    }

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

    public void updateList(List<User> newList) {
        mAsyncListDiffer.submitList(newList);
    }

}

User.java

public class User {

    private String mUserId;
    private Uri mImageUrl;

    public User(String userId, String imageUrl) {
        mUserId = userId;
        mImageUrl = Uri.parse(imageUrl);
    }

    public String getUserId() {
        return mUserId;
    }

    public Uri getImageUrl() {
        return mImageUrl;
    }

    @Override
    public boolean equals(Object other) {
        if (other instanceof User) {
            User user = (User) other;
            return mUserId.equals(user.getUserId()) && mImageUrl.equals(user.getImageUrl());
        } else {
            return false;
        }
    }

}

关于java - 我的DiffUtil实现有什么问题？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/54162101/