android - RecyclerView 在回收时导致问题

Question

我有一个使用 RecyclerView 创建的项目列表。当用户单击其中一个时，我会更改该选定项目的背景颜色。问题是，当我滚动浏览我的项目并且它们被回收时，一些项目获得了所选项目的背景颜色(这是错误的)。在这里你可以看到我的 Adapter 的代码:

public class OrderAdapter extends RecyclerView.Adapter<OrderAdapter.ViewHolder> {

private static final String SELECTED_COLOR = "#ffedcc";

private List<OrderModel> mOrders;

public OrderAdapter() {
    this.mOrders = new ArrayList<>();
}

public void setOrders(List<OrderModel> orders) {
    mOrders = orders;
}

public void addOrders(List<OrderModel> orders) {
    mOrders.addAll(0, orders);
}

public void addOrder(OrderModel order) {
    mOrders.add(0, order);
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    Context context = parent.getContext();
    LayoutInflater inflater = LayoutInflater.from(context);

    // Inflate the custom layout
    View contactView = inflater.inflate(R.layout.order_main_item, parent, false);

    // Return a new holder instance
    ViewHolder viewHolder = new ViewHolder(contactView);
    return viewHolder;
}

@Override
public void onBindViewHolder(final ViewHolder viewHolder, final int position) {
    final OrderModel orderModel = mOrders.get(position);

    // Set item views based on the data model
    TextView customerName = viewHolder.customerNameText;

    SimpleDateFormat simpleDateFormat = new SimpleDateFormat("MM/dd/yyyy'   'HH:mm:ss:S");
    String time = simpleDateFormat.format(orderModel.getOrderTime());
    customerName.setText(time);

    TextView orderNumber = viewHolder.orderNumberText;
    orderNumber.setText("Order No: " + orderModel.getOrderNumber());

    Button button = viewHolder.acceptButton;
    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            viewHolder.userActions.acceptButtonClicked(position);
        }
    });

    final LinearLayout orderItem = viewHolder.orderItem;
    orderItem.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            viewHolder.userActions.itemClicked(orderModel);
            viewHolder.orderItem.setBackgroundColor(Color.parseColor(SELECTED_COLOR));
        }
    });
}

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


public static class ViewHolder extends RecyclerView.ViewHolder implements OrderContract.View {

    public TextView customerNameText;
    public Button acceptButton;
    public TextView orderNumberText;
    public OrderContract.UserActions userActions;
    public LinearLayout orderItem;

    public ViewHolder(View itemView) {
        super(itemView);

        userActions = new OrderPresenter(this);

        customerNameText = (TextView) itemView.findViewById(R.id.customer_name);
        acceptButton = (Button) itemView.findViewById(R.id.accept_button);
        orderNumberText = (TextView) itemView.findViewById(R.id.order_number);
        orderItem = (LinearLayout) itemView.findViewById(R.id.order_item_selection);
    }

    @Override
    public void removeItem() {

    }
}

Answer 1

问题是 recyclerView 回收行为，它将屏幕外的 ViewHolder 项目分配给即将显示在屏幕上的新项目。我不建议您像上述所有答案那样基于 ViewHolder 对象绑定(bind)您的逻辑。它真的会给你带来麻烦。您应该根据数据对象的状态构建逻辑，而不是 ViewHolder 对象，因为您永远不知道它何时被回收。

假设你保存了一个在 ViewHolder 中状态 boolean isSelected 进行检查，但是如果它是真的，那么当这个 viewHolder 将被回收。

更好的方法是在 DataModel 对象中保存任何状态。在您的例子中，只有一个 boolean isSelected。

示例如

package chhimwal.mahendra.multipleviewrecyclerproject;

import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.support.v7.widget.CardView;
import android.widget.TextView;

import java.util.List;

/**
 * Created by mahendra.chhimwal on 12/10/2015.
 */
public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.ViewHolder> {

    private Context mContext;
    private List<DataModel> mRViewDataList;


    public MyRecyclerViewAdapter(Context context, List<DataModel> rViewDataList) {
        this.mContext = context;
        this.mRViewDataList = rViewDataList;
    }

    @Override
    public MyRecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        LayoutInflater inflater = LayoutInflater.from(parent.getContext());
        View view = inflater.inflate(R.layout.item_recycler_view, parent, false);
        return new ViewHolder(view);
    }

    @Override
    public void onBindViewHolder(ViewHolder holder, int position) {
        holder.bindDataWithViewHolder(mRViewDataList.get(position));
    }

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


    public class ViewHolder extends RecyclerView.ViewHolder {
        private TextView textView;
        private LinearLayout llView;
        private DataModel mDataItem=null;

        public ViewHolder(View itemView) {
            super(itemView);
            llView=(LinearLayout)itemView.findViewById(R.id.ll_root_view);
            textView = (TextView) itemView.findViewById(R.id.tvItemName);
            cvItemView.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                  // One should handle onclick of event here based on the dataItem i.e. mDataItem in this case.
                  // something like that..
                /* Intent intent = new Intent(mContext,ResultActivity.class);
                 intent.putExtra("MY_DATA",mDataItem);   //If you want to pass data.
                 intent.putExtra("CLICKED_ITEM_POSTION",getAdapterPosition()); // If one want to get selected item position
                 startActivity(intent);*/
                 Toast.makeText(mContext,"You clicked item number "+ViewHolder.this.getAdapterPosition(),Toast.LENTH_SHORT).show();
                }
            });
        }

        //This is clean method to bind data with viewHolder. Do all dirty things on View based on dataItem.
        //Must be called from onBindViewHolder(),with dataItem. In our case dataItem is String object.
        public void bindDataWithViewHolder(DataModel dataItem){
            this.mDataItem=dataItem;

            if(mDataItem.isSelected()){
                llView.setBackgroundColor(Color.ParseColor(SELCTED_COLOR);
            }else{
                llView.setBackgroundColor(Color.ParseColor(DEFAULT_COLOR);
            }
            //other View binding logics like setting text , loading image  etc.
            textView.setText(mDataItem);
        }
    }
}

正如@Gabriel 在评论中所问的那样，

what if one want to select a single item at time?

在那种情况下，同样不应将所选项目状态保存在 ViewHolder 对象中，因为它会被回收并导致问题。更好的方法是在 Adapter 类中有一个字段 int selectedItemPosition 而不是 ViewHolder 。以下代码 fragment 显示了它。

public class MyRecyclerViewAdapter extends RecyclerView.Adapter<MyRecyclerViewAdapter.ViewHolder> {



        private Context mContext;
        private List<DataModel> mRViewDataList;

        //variable to hold selected Item position
        private int mSelectedItemPosition = -1;


        public MyRecyclerViewAdapter(Context context, List<DataModel> rViewDataList) {
            this.mContext = context;
            this.mRViewDataList = rViewDataList;
        }

        @Override
        public MyRecyclerViewAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
            LayoutInflater inflater = LayoutInflater.from(parent.getContext());
            View view = inflater.inflate(R.layout.item_recycler_view, parent, false);
            return new ViewHolder(view);
        }

        @Override
        public void onBindViewHolder(ViewHolder holder, int position) {
            holder.bindDataWithViewHolder(mRViewDataList.get(position),position);
        }

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


        public class ViewHolder extends RecyclerView.ViewHolder {
            private TextView textView;
            private LinearLayout llView;
            private DataModel mDataItem=null;

            public ViewHolder(View itemView) {
                super(itemView);
                llView=(LinearLayout)itemView.findViewById(R.id.ll_root_view);
                textView = (TextView) itemView.findViewById(R.id.tvItemName);
                cvItemView.setOnClickListener(new View.OnClickListener() {
                    @Override
                    public void onClick(View v) {
                        //Handling for background selection state changed
                        int previousSelectState=mSelectedItemPosition;
                        mSelectedItemPosition = getAdapterPosition();
                        //notify previous selected item
                        notifyItemChanged(previousSelectState);
                        //notify new selected Item
                        notifyItemChanged(mSelectedItemPosition);

                        //Your other handling in onclick

                    }
                });
            }

            //This is clean method to bind data with viewHolder. Do all dirty things on View based on dataItem.
            //Must be called from onBindViewHolder(),with dataItem. In our case dataItem is String object.
            public void bindDataWithViewHolder(DataModel dataItem, int currentPosition){
                this.mDataItem=dataItem;
                //Handle selection  state in object View.
                if(currentPosition == mSelectedItemPosition){
                    llView.setBackgroundColor(Color.ParseColor(SELCTED_COLOR);
                }else{
                    llView.setBackgroundColor(Color.ParseColor(DEFAULT_COLOR);
                }
                //other View binding logics like setting text , loading image  etc.
                textView.setText(mDataItem);
            }
        }
    }

如果您只需要维护选定的项目状态，我强烈反对使用 Adapter 类的 notifyDataSetChanged() 方法，因为 RecyclerView 为这些情况提供了更大的灵 active 。