Android：如何将EditText的text属性传入其他View的DataBinding表达式

问题详情 #

布局内包含ID为quantityNumber的EditText（数量输入框）和ID为addToCartButton的Button，期望通过DataBinding在Button点击时将EditText的数值传递给ViewModel的onAddButtonClicked方法。尝试了两种写法：

android:onClick="@{() -> productDetailViewModel.onAddButtonClicked(quantityNumber.getText())}"

或

android:onClick="@{() -> productDetailViewModel.onAddButtonClicked(quantityNumber.text)}"

但编译时始终报错：

error: cannot find symbol
import com.example.checkoutexample.databinding.FragmentProductDetailBindingImpl;
                                              ^
  symbol:   class FragmentProductDetailBindingImpl
  location: package com.example.checkoutexample.databinding

布局代码 #

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    tools:context=".ProductDetailFragment">

    <data>
        <variable
            name="productDetailViewModel"
            type="com.example.checkoutexample.ProductDetailViewModel" />
    </data>

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical">

            <ImageView
                android:id="@+id/productImage"
                android:layout_width="match_parent"
                android:layout_height="300dp"
                android:layout_gravity="center"
                android:scaleType="centerCrop"
                android:src="@drawable/cupcake"
                tools:src="@tools:sample/backgrounds/scenic" />

            <TextView
                android:id="@+id/productTitle"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="@dimen/margin_small"
                android:layout_marginTop="@dimen/margin_small"
                android:text="@string/hazelnut_cupcakes"
                android:textSize="30sp" />

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="@dimen/margin_medium"
                android:orientation="horizontal">

                <TextView
                    android:id="@+id/productPrice"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginStart="@dimen/margin_small"
                    android:text="@string/product_price"
                    android:textSize="20sp" />

                <TextView
                    android:id="@+id/stockCountMessage"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginStart="@dimen/margin_medium"
                    android:textColor="@{productDetailViewModel.remainingStock == 0 ? @color/red : @color/blue}"
                    android:textSize="15sp"
                    android:textStyle="italic"
                    android:text="@{productDetailViewModel.remainingStock == 0 ? @string/out_of_stock : @string/stock_msg(productDetailViewModel.remainingStock)}"
                    tools:text="(5 items left)" />
            </LinearLayout>

            <TextView
                android:id="@+id/productDescription"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginStart="@dimen/margin_small"
                android:layout_marginTop="@dimen/margin_small"
                android:text="@string/product_description" />

            <TextView
                android:id="@+id/quantityLabel"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginStart="@dimen/margin_small"
                android:layout_marginTop="@dimen/margin_small"
                android:text="@string/quantity" />

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:orientation="horizontal">

                <EditText
                    android:id="@+id/quantityNumber"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginStart="@dimen/margin_small"
                    android:ems="2"
                    android:gravity="center"
                    android:inputType="number"
                    android:minWidth="48dp"
                    android:minHeight="48dp"
                    android:text="@string/quantity_1" />

                <Button
                    android:id="@+id/addToCartButton"
                    android:layout_width="wrap_content"
                    android:layout_height="wrap_content"
                    android:layout_marginStart="@dimen/margin_small"
                    android:enabled="@{productDetailViewModel.remainingStock == 0 ? false : true}"
                    android:onClick="@{() -> productDetailViewModel.onAddButtonClicked(quantityNumber.getText())}"
                    android:text="@string/add" />
            </LinearLayout>

        <Button
            android:id="@+id/checkoutButton"
            android:layout_width="@dimen/button_width"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_marginTop="@dimen/margin_large"
            android:text="@{@string/checkout(productDetailViewModel.orderTotal)}"
            android:textSize="20sp" />

        </LinearLayout>
    </ScrollView>
</layout>

Fragment代码 #

class ProductDetailFragment : Fragment() {

    private var _binding: FragmentProductDetailBinding? = null
    private val binding get() = _binding!!
    private lateinit var viewModel: ProductDetailViewModel
    private var stockLeft = 0

    override fun onCreateView(
        inflater: LayoutInflater, container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View {
        _binding = FragmentProductDetailBinding.inflate(inflater, container, false)
        val view = binding.root
        viewModel = ViewModelProvider(this)[ProductDetailViewModel::class.java]

        binding.apply {
            productDetailViewModel = viewModel
            lifecycleOwner = viewLifecycleOwner

            viewModel.orderTotal.observe(viewLifecycleOwner) { orderTotal ->
                with(checkoutButton) {
                    setOnClickListener {
                        val action =
                            ProductDetailFragmentDirections.actionProductDetailFragmentToShoppingCartFragment(
                                orderTotal
                            )
                        view.findNavController().navigate(action)
                    }
                }
            }

            viewModel.insufficientStock.observe(viewLifecycleOwner) { insufficientStock ->
                if (insufficientStock) {
                    Toast.makeText(
                        context,
                        getString(R.string.low_stock_error, viewModel.remainingStock.value),
                        Toast.LENGTH_LONG
                    ).show()
                }
            }

            addToCartButton.setOnClickListener {
// Would like to replace these two lines with DataBinding
//                val orderQuantity = quantityNumber.text.toString().toInt()
//                viewModel.onAddButtonClicked(orderQuantity)

                hideKeyboard(view)
            }
        }

        return view
    }

    private fun hideKeyboard(view: View) {
        val inputMethodManager =
            activity?.getSystemService(Context.INPUT_METHOD_SERVICE) as InputMethodManager
        inputMethodManager.hideSoftInputFromWindow(view.windowToken, 0)
    }
}

解决步骤 #

1. 修正DataBinding表达式的类型转换 #

ViewModel的onAddButtonClicked方法需要接收Int类型参数，但EditText的text属性返回的是Editable，直接传递会导致类型不兼容，这是编译失败的核心原因。修改Button的onClick表达式：

android:onClick="@{() -> productDetailViewModel.onAddButtonClicked(quantityNumber.text.isEmpty() ? 1 : Integer.parseInt(quantityNumber.text.toString()))}"

这段代码会先判断输入是否为空，为空则默认传1，否则把文本转成Int传递。

2. 移除Fragment中重复的点击监听 #

Fragment里手动给addToCartButton设置的点击监听会覆盖DataBinding的绑定逻辑，导致DataBinding的点击事件不生效，直接删除这段代码：

addToCartButton.setOnClickListener {
// Would like to replace these two lines with DataBinding
//                val orderQuantity = quantityNumber.text.toString().toInt()
//                viewModel.onAddButtonClicked(orderQuantity)

                hideKeyboard(view)
            }

如果需要隐藏键盘，可以把hideKeyboard逻辑移到ViewModel的onAddButtonClicked方法中，或者通过BindingAdapter实现点击时隐藏键盘的通用逻辑。

3. 清理编译缓存并重新构建 #

BindingImpl类找不到通常是编译缓存问题，执行以下操作：

• 点击Android Studio顶部菜单栏的Build -> Clean Project
• 再点击Build -> Rebuild Project
• 若仍未解决，删除项目根目录下的.gradle文件夹和模块内的build文件夹，然后重新编译

4. 确认ViewModel方法参数类型 #

确保ProductDetailViewModel中的onAddButtonClicked方法参数为Int类型：

fun onAddButtonClicked(quantity: Int) {
    // 处理添加购物车的业务逻辑
    // 若需要隐藏键盘，可通过Context调用隐藏方法
}

内容的提问来源于stack exchange，提问作者Daniel