main:

public class MainActivity extends AppCompatActivity implements DataCall<List<Shop>> {

    private TextView mSumPrice;
    private TextView mCount;
    private RecyclerView mLeftRecycler,mRightRecycler;

    private LeftAdapter mLeftAdapter;
    private RightAdapter mRightAdapter;

    private CartPresenter cartPresenter = new CartPresenter(this);

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mSumPrice = findViewById(R.id.goods_sum_price);
        mCount = findViewById(R.id.goods_number);
        mLeftRecycler = findViewById(R.id.left_recycler);
        mRightRecycler = findViewById(R.id.right_recycler);

        mLeftRecycler.setLayoutManager(new LinearLayoutManager(this));
        mRightRecycler.setLayoutManager(new LinearLayoutManager(this));

        mLeftAdapter = new LeftAdapter();
        mLeftAdapter.setOnItemClickListenter(new LeftAdapter.OnItemClickListenter() {
            @Override
            public void onItemClick(Shop shop) {
                mRightAdapter.clearList();//清空資料
                mRightAdapter.addAll(shop.getList());
                mRightAdapter.notifyDataSetChanged();
            }
        });
        mLeftRecycler.setAdapter(mLeftAdapter);
        mRightAdapter = new RightAdapter();
        mRightAdapter.setOnNumListener(new RightAdapter.OnNumListener() {
            @Override
            public void onNum() {
                calculatePrice(mLeftAdapter.getList());
            }
        });
        mRightRecycler.setAdapter(mRightAdapter);

        cartPresenter.requestData();

    }

    @Override
    public void success(List<Shop> data) {
        calculatePrice(data);//計算價格和數量

        mLeftAdapter.addAll(data);//左邊的新增型別

        //得到預設選中的shop，設定上顏色和背景
        Shop shop = data.get(1);
        shop.setTextColor(0xff000000);
        shop.setBackground(R.color.white);
        mRightAdapter.addAll(shop.getList());



        mLeftAdapter.notifyDataSetChanged();
        mRightAdapter.notifyDataSetChanged();
    }

    @Override
    public void fail(Result result) {
        Toast.makeText(this, result.getCode() + "   " + result.getMsg(), Toast.LENGTH_LONG).show();
    }

    /**
     * @author dingtao
     * @date 2018/12/18 7:01 PM
     * 計算總價格
     */
    private void calculatePrice(List<Shop> shopList){
        double totalPrice=0;
        int totalNum = 0;
        for (int i = 0; i < shopList.size(); i++) {//迴圈的商家
            Shop shop = shopList.get(i);
            for (int j = 0; j < shop.getList().size(); j++) {
                Goods goods = shop.getList().get(j);
                //計算價格
                totalPrice = totalPrice + goods.getNum() * goods.getPrice();
                totalNum+=goods.getNum();//計數
            }
        }
        mSumPrice.setText("價格："+totalPrice);
        mCount.setText(""+totalNum);
    }
}
 

LeftAdapter:

public class LeftAdapter extends RecyclerView.Adapter<LeftAdapter.MyHolder> {

    private List<Shop> mList = new ArrayList<>();

    public void addAll(List<Shop> list){
        mList.addAll(list);
    }

    @NonNull
    @Override
    public MyHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view = View.inflate(viewGroup.getContext(), R.layout.recycler_left_item,null);
        MyHolder myHolder = new MyHolder(view);
        return myHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull final MyHolder myHolder, int i) {
        final Shop shop = mList.get(i);
        myHolder.text.setText(shop.getSellerName());
        myHolder.text.setBackgroundResource(shop.getBackground());
        myHolder.text.setTextColor(shop.getTextColor());
        myHolder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                for (int j = 0; j <mList.size() ; j++) {
                    mList.get(j).setTextColor(0xffffffff);
                    mList.get(j).setBackground(R.color.grayblack);
                }
                shop.setBackground(R.color.white);
                shop.setTextColor(0xff000000);
                notifyDataSetChanged();
                onItemClickListenter.onItemClick(shop);//切換右邊的列表
            }
        });
    }

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

    public List<Shop> getList() {
        return mList;
    }

    class MyHolder extends RecyclerView.ViewHolder{

        TextView text;

        public MyHolder(@NonNull View itemView) {
            super(itemView);
            text = itemView.findViewById(R.id.left_text);
        }
    }

    private OnItemClickListenter onItemClickListenter;

    public void setOnItemClickListenter(OnItemClickListenter onItemClickListenter) {
        this.onItemClickListenter = onItemClickListenter;
    }

    public interface OnItemClickListenter{
        void onItemClick(Shop shop);
    }
}
 

RightAdapter:

public class RightAdapter extends RecyclerView.Adapter<RightAdapter.ChildHolder> {

    private List<Goods> mList = new ArrayList<>();

    public void addAll(List<Goods> list) {
        mList.addAll(list);
    }

    @NonNull
    @Override
    public ChildHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {
        View view = View.inflate(viewGroup.getContext(), R.layout.recycler_right_item, null);
        ChildHolder myHolder = new ChildHolder(view);
        return myHolder;
    }

    @Override
    public void onBindViewHolder(@NonNull ChildHolder childHolder, int position) {

        final Goods goods = mList.get(position);
        childHolder.text.setText(goods.getTitle());
        childHolder.price.setText("單價：" + goods.getPrice());//單價

        String imageurl = "https" + goods.getImages().split("https")[1];
        Log.i("dt", "imageUrl: " + imageurl);
        imageurl = imageurl.substring(0, imageurl.lastIndexOf(".jpg") + ".jpg".length());
        Glide.with(MApp.getInstance()).load(imageurl).into(childHolder.image);//載入圖片

        childHolder.addSub.setCount(goods.getNum());//設定商品數量
        childHolder.addSub.setAddSubListener(new AddSubLayout.AddSubListener() {
            @Override
            public void addSub(int count) {
                goods.setNum(count);
                onNumListener.onNum();//計算價格
            }
        });
    }

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

    public void clearList() {
        mList.clear();
    }


    class ChildHolder extends RecyclerView.ViewHolder {

        TextView text;
        TextView price;
        ImageView image;
        AddSubLayout addSub;

        public ChildHolder(@NonNull View itemView) {
            super(itemView);
            text = itemView.findViewById(R.id.text);
            price = itemView.findViewById(R.id.text_price);
            image = itemView.findViewById(R.id.image);
            addSub = itemView.findViewById(R.id.add_sub_layout);
        }
    }

    private OnNumListener onNumListener;

    public void setOnNumListener(OnNumListener onNumListener) {
        this.onNumListener = onNumListener;
    }

    public interface OnNumListener{
        void onNum();
    }
}
 

加減自定義view:

public class AddSubLayout extends LinearLayout implements View.OnClickListener {


    private TextView mAddBtn,mSubBtn;
    private TextView mNumText;
    private AddSubListener addSubListener;

    public AddSubLayout(Context context) {
        super(context);
        initView();
    }

    public AddSubLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public AddSubLayout(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        initView();
    }


    private void initView(){
        //載入layout佈局，第三個引數ViewGroup一定寫成this
        View view = View.inflate(getContext(),R.layout.car_add_sub_layout,this);

        mAddBtn = view.findViewById(R.id.btn_add);
        mSubBtn = view.findViewById(R.id.btn_sub);
        mNumText = view.findViewById(R.id.text_number);
        mAddBtn.setOnClickListener(this);
        mSubBtn.setOnClickListener(this);

    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        super.onLayout(changed, l, t, r, b);

        int width = r-l;//getWidth();
        int height = b-t;//getHeight();

    }

    @Override
    public void onClick(View v) {
        int number = Integer.parseInt(mNumText.getText().toString());

        switch (v.getId()){
            case R.id.btn_add:
                number++;
                mNumText.setText(number+"");
                break;
            case R.id.btn_sub:
                if (number==0){
                    Toast.makeText(getContext(),"數量不能小於0",Toast.LENGTH_LONG).show();
                    return;
                }
                number--;
                mNumText.setText(number+"");
                break;
        }
        if (addSubListener!=null){
            addSubListener.addSub(number);
        }
    }

    public void setCount(int count) {
        mNumText.setText(count+"");
    }

    public void setAddSubListener(AddSubListener addSubListener) {
        this.addSubListener = addSubListener;
    }

    public interface AddSubListener{
        void addSub(int count);
    }
}