我正在使用 MVVM 架构来构建一个简单的订购应用程序。我在 ProductsFragment 中使用 RecyclerView 来列出所有可以订购的产品。我还在我的 ViewModel 中使用 LiveData 并在我的 Fragment 中使用 observable 来检查产品列表的任何更改。
在我的列表项中,我有 3 个按钮:1 个按钮用于将产品添加到购物篮,另一个按钮用于增加客户想要添加到购物篮的数量,第三个按钮用于减少客户想要添加到购物篮的数量。
在我的产品数据类中,每当客户单击增量或减量按钮时,数据模型中的数量就会更新。
我还使用数据绑定将产品绑定到 recyclerview 列表项布局和单击侦听器。我正在使用 ListAdapter 来直接访问 DiffUtil。
我遇到的问题是,当通知 observable 时,我想使用 ListAdapter 的 SubmitList 方法,因此只有已更改的项目才会在 RecyclerView 中更新。但是,我注意到 DiffUtil 方法 areContentsTheSame() 始终返回 true。因此列表项不会更新。我不想使用notifyDatasetChanged,因为这会阻塞UI 线程。
我遇到的另一个问题是,当我将产品添加到购物篮时,对产品的引用将被保留,因此当我将产品添加到购物篮时,MutableLiveData 也会更新,而我只想更新 MutableLiveData。将产品添加到购物篮时,如何停止对正在创建的 LiveData 的引用?
产品视图模型
class ProductsViewModel : ViewModel() {
// LIVE DATA
private val _basket = MutableLiveData<Basket>()
val basket: LiveData<Basket>
get() = _basket
private val _products = MutableLiveData<List<Product>>()
val products: LiveData<List<Product>>
get() = _products
init {
_basket.value = Basket()
_products.value = dummyData
}
fun onIncrementProductQuantityButtonPressed(product: Product) {
//product.quantity += 1
//val newList = _products.value
//_products.value = newList
val newProduct = product.copy(quantity = product.quantity.plus(1))
_basket.value!!.updateProductInBasket(newProduct)
_basket.value = _basket.value
}
fun onDecrementProductQuantityButtonPressed(product: Product) {
if (product.quantity>1) {
//product.quantity = product.quantity.minus(1)
val newProduct = product.copy(quantity = product.quantity.minus(1))
_basket.value!!.updateProductInBasket(newProduct)
_basket.value = _basket.value
}
}
}
产品片段
class ProductsFragment : Fragment() {
private lateinit var viewModel: ProductsViewModel
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?): View? {
// Inflate the layout for this fragment
val binding: FragmentProductsBinding = DataBindingUtil.inflate(
inflater, R.layout.fragment_products, container, false)
viewModel = ViewModelProviders.of(this).get(ProductsViewModel::class.java)
val adapter = ProductsAdapter(ProductListener { product, onClickType ->
when(onClickType) {
OnClickType.INCREMENT -> {
viewModel.onIncrementProductQuantityButtonPressed(product)
}
OnClickType.DECREMENT -> {
viewModel.onDecrementProductQuantityButtonPressed(product)
}
OnClickType.BASKET -> {
viewModel.addToBasketButtonPressed(product)
}
}
})
viewModel.products.observe(this, Observer { list ->
adapter.submitList(list)
//adapter.notifyDataSetChanged() // TODO: check why I have to do notifyDataSetChanged()
})
viewModel.basket.observe(this, Observer {
activity?.invalidateOptionsMenu()
})
binding.viewModel = viewModel
binding.lifecycleOwner = this
binding.productsRecyclerView.adapter = adapter
setHasOptionsMenu(true)
return binding.root
}
产品适配器
class ProductsAdapter(private val clickListener: ProductListener) : ListAdapter<Product, ProductsAdapter.ProductViewHolder>(ProductDiffUtil()) {
class ProductDiffUtil: DiffUtil.ItemCallback<Product>() {
override fun areItemsTheSame(oldItem: Product, newItem: Product): Boolean {
Log.d("Products", "Are items the same")
return oldItem.name == newItem.name && oldItem.size == newItem.size
}
override fun areContentsTheSame(oldItem: Product, newItem: Product): Boolean {
Log.d("Products", "Are contents the same ${oldItem == newItem}")
Timber.d("Are contents the same ${oldItem == newItem}")
Timber.d("OLD ITEM: $oldItem")
Timber.d("NEW ITEM: $newItem")
return oldItem == newItem //need to check this
}
}
override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ProductViewHolder {
return ProductViewHolder.from(parent)
}
override fun onBindViewHolder(holder: ProductViewHolder, position: Int) {
val item = getItem(position)
//use holder to access all the views in the card item
holder.bind(clickListener, item)
}
class ProductViewHolder private constructor(private val binding: LayoutProductCardBinding) : RecyclerView.ViewHolder(binding.root) {
fun bind(clickListener: ProductListener, item: Product) {
binding.product = item
binding.clickListener = clickListener
binding.executePendingBindings()
}
companion object {
fun from(parent: ViewGroup): ProductViewHolder {
val layoutInflater = LayoutInflater.from(parent.context)
val binding = LayoutProductCardBinding.inflate(layoutInflater, parent, false)
return ProductViewHolder(binding)
}
}
}
}
class ProductListener(val clickListener: (product: Product, clickType: OnClickType) -> Unit) {
fun onAddToBasket(product: Product) = clickListener(product, OnClickType.BASKET)
fun onDecrementProductQuantity(product: Product) = clickListener(product, OnClickType.DECREMENT)
fun onIncrementProductQuantity(product: Product) = clickListener(product, OnClickType.INCREMENT)
}
enum class OnClickType { BASKET, DECREMENT, INCREMENT }