用Kotlin写一个项目第一个Fragment包含一个RecyclerView,每个item的界面为左侧一个水果图 像，右侧显示水果名称和单价，点击任一item可显示第二个Fragment,如 图1a； •第二个Fragment界面如图1b所示，点击其中的“+”，“-“键可更改订 单数量；

•订单数量可以为0-100之间的任意整数，金额根据数量动态计算，保留两位小数；

•购买数量发生变化时，第一个Fragment中对应的水果item右侧单价也需要更新。

1a

1b

以下是Kotlin代码实现：

第一个Fragment：

class FruitListFragment : Fragment() {
    private lateinit var binding: FragmentFruitListBinding
    private lateinit var fruitList: List<Fruit>
    private lateinit var adapter: FruitListAdapter

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        binding = FragmentFruitListBinding.inflate(inflater, container, false)
        initData()
        initView()
        return binding.root
    }

    private fun initData() {
        fruitList = listOf(
            Fruit("苹果", 5.8, R.drawable.apple),
            Fruit("香蕉", 2.5, R.drawable.banana),
            Fruit("橙子", 3.2, R.drawable.orange),
            Fruit("草莓", 8.7, R.drawable.strawberry)
        )
    }

    private fun initView() {
        adapter = FruitListAdapter(fruitList) { position -> toOrderFragment(position) }
        binding.recyclerView.adapter = adapter
        binding.recyclerView.layoutManager = LinearLayoutManager(context)
    }

    private fun toOrderFragment(position: Int) {
        val fruit = fruitList[position]
        parentFragmentManager.beginTransaction().apply {
            replace(R.id.fragment_container, OrderFragment.newInstance(fruit))
            addToBackStack(null)
            commit()
        }
    }
}

第一个Fragment中RecyclerView的适配器：

class FruitListAdapter(
    private val fruitList: List<Fruit>,
    private val onItemClickListener: (Int) -> Unit
) : RecyclerView.Adapter<FruitListAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val inflater = LayoutInflater.from(parent.context)
        val binding = ItemFruitBinding.inflate(inflater, parent, false)
        return ViewHolder(binding)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val fruit = fruitList[position]
        holder.binding.ivFruit.setImageResource(fruit.icon)
        holder.binding.tvFruitName.text = fruit.name
        holder.binding.tvPrice.text = String.format("%.2f 元/kg", fruit.price)
        holder.itemView.setOnClickListener { onItemClickListener(position) }
    }

    override fun getItemCount(): Int {
        return fruitList.size
    }

    inner class ViewHolder(val binding: ItemFruitBinding) : RecyclerView.ViewHolder(binding.root)
}

第二个Fragment：

class OrderFragment : Fragment() {
    private lateinit var binding: FragmentOrderBinding
    private lateinit var fruit: Fruit
    private var quantity = 0

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {
        binding = FragmentOrderBinding.inflate(inflater, container, false)
        initArguments()
        initViews()
        return binding.root
    }

    private fun initArguments() {
        fruit = requireArguments().getParcelable(ARG_FRUIT)!!
    }

    private fun initViews() {
        binding.ivFruit.setImageResource(fruit.icon)
        binding.tvFruitName.text = fruit.name
        binding.tvPrice.text = String.format("%.2f 元/kg", fruit.price)
        binding.tvQuantity.text = quantity.toString()

        binding.btnMinus.setOnClickListener {
            if (quantity > 0) {
                quantity--
                updateOrder()
            }
        }

        binding.btnAdd.setOnClickListener {
            if (quantity < 100) {
                quantity++
                updateOrder()
            }
        }
    }

    private fun updateOrder() {
        binding.tvQuantity.text = quantity.toString()
        val totalPrice = fruit.price * quantity
        binding.tvTotalPrice.text = String.format("%.2f 元", totalPrice)
        (requireActivity() as MainActivity).updateCartItem(fruit, quantity)
    }

    companion object {
        private const val ARG_FRUIT = "fruit"

        fun newInstance(fruit: Fruit): OrderFragment {
            val args = Bundle().apply {
                putParcelable(ARG_FRUIT, fruit)
            }
            return OrderFragment().apply {
                arguments = args
            }
        }
    }
}

第二个Fragment中显示订单信息的布局：

<LinearLayout
  android:orientation="horizontal"
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:layout_marginTop="16dp"
  android:gravity="center">

  <TextView
    android:id="@+id/tv_quantity_label"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="购买数量：" />

  <Button
    android:id="@+id/btn_minus"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="-" />

  <TextView
    android:id="@+id/tv_quantity"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="8dp"
    android:text="0"
    android:textColor="#000000"
    android:textSize="16sp" />

  <Button
    android:id="@+id/btn_add"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="+" />

  <TextView
    android:id="@+id/tv_total_price"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginStart="16dp"
    android:text="0 元"
    android:textSize="16sp" />

</LinearLayout>

MainActivity中的updateCartItem方法用来更新购物车列表：

fun updateCartItem(fruit: Fruit, quantity: Int) {
    val index = cartItems.indexOfFirst { it.fruit == fruit }

    if (index == -1) {
        if (quantity > 0) {
            cartItems.add(CartItem(fruit, quantity))
        }
    } else {
        if (quantity > 0) {
            cartItems[index].quantity = quantity
        } else {
            cartItems.removeAt(index)
        }
    }

    adapter.notifyDataSetChanged()
}

购物车列表的RecyclerView的适配器：

class CartListAdapter(
    private val cartItemList: List<CartItem>
) : RecyclerView.Adapter<CartListAdapter.ViewHolder>() {

    override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder {
        val inflater = LayoutInflater.from(parent.context)
        val binding = ItemCartItemBinding.inflate(inflater, parent, false)
        return ViewHolder(binding)
    }

    override fun onBindViewHolder(holder: ViewHolder, position: Int) {
        val cartItem = cartItemList[position]
        holder.binding.ivFruit.setImageResource(cartItem.fruit.icon)
        holder.binding.tvFruitName.text = cartItem.fruit.name
        holder.binding.tvPrice.text = String.format("%.2f 元/kg", cartItem.fruit.price)
        holder.binding.tvQuantity.text = cartItem.quantity.toString()
        holder.binding.tvTotalPrice.text = String.format(
            "%.2f 元", cartItem.fruit.price * cartItem.quantity
        )
    }

    override fun getItemCount(): Int {
        return cartItemList.size
    }

    inner class ViewHolder(val binding: ItemCartItemBinding) : RecyclerView.ViewHolder(binding.root)
}