我的DiffUtil实现有什么问题？

时间：2019-01-12 17:28:07

标签： java android android-recyclerview recycler-adapter android-diffutils

更新：解决了一个问题：现在updateList已解决，问题是我将mAdapter定义为RecyclerView.Adapter而不是{{1 }}。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MyAdapter更新我的RecyclerView以防止重复。

我有4个类：User类，设置数据的DiffUtil类，Activity类和Adapter类。我不确定我是否能正确组合所有这四个。

这是User类：

DiffUtil

这是我动态设置数据的方式（我不断从包含要显示用户ID的服务器上获取新的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; } } 数组，然后从Json存储中设置用户图像）：（这是一个功能由onClick侦听器调用：）

这是片段中的方法调用：

Firebase

这是功能：

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

这是我的 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); } } } 类的样子：

DiffUtil

这是我的适配器：

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);
    }
}

我不确定我是否正确组合了所有类（我第一次使用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); } } ），我也得到了DiffUtil

我在做什么错？

这是我在Fragment中定义mAdapter的方式：

cannot resolve method updateList(?)

4 个答案:

答案 0 :(得分：6)

问题来自mAdapter的定义。您将其定义为RecyclerView.Adapter的超类MyAdapter，并且其中不包含updateList()。您应该将其更改如下：

private MyAdapter mAdapter;

更新1/13/2019：

我用AsyncListDiffer重写了您的适配器，该适配器异步计算了差异，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;
        }
    }

}

答案 1 :(得分：1)

除了@aminography的答案，我建议您使用ListAdapter，这是一种RecyclerView.Adapter的实现，可以更轻松地用正确的动画更新RecyclerView。此类包含在recyclerview支持库中。

以下是根据您的用例使用的示例：

public class MyAdapter extends ListAdapter<User, UserViewHolder> {
    public MyAdapter() {
        super(new UserDiffCallback());
    }

    public UserViewHolder onCreateViewHolder(int position, int viewType) { ... }

    public void onBindViewHolder(UserViewModel holder, int position) {
        User userAtPosition = getItem(position); // getItem is a protected method from ListAdapter
        // Bind user data to your holder...
    }
}

public class UserDiffCallback extends DiffUtil.ItemCallback<User> {

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

    @Override
    public boolean areContentsTheSame(@NonNull User oldUser, @NonNull User newUser) {
        // No need to check the equality for all User fields ; just check the equality for fields that change the display of your item.
        // In your case, both impact the display.
        return oldUser.getUserId().equals(newUser.getUserId()) 
                && (oldUser.getImageUrl() == null) ? newUser.getImageUrl() == null : oldUser.getImageUrl().equals(newUser.getImageUrl());
    }
}

然后，当您需要使用新用户更新列表时，请致电myAdapter.submitList(newList)。就像AsyncListDiffer一样，两个列表之间的差异是在后台线程上计算的。

答案 2 :(得分：0)

看起来像
public void onBindViewHolder(@NonNull ViewHolder holder, int position, @NonNull List<Object> payloads)未实施 实施此操作以正确使用DiffUtils，因为将对此更改进行调用，并且基于有效负载，您可以更新recyclerview项，而不用调用notifyDataSetChanged（）

答案 3 :(得分：0)

修改您的方法：

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