在 xml 中设置/观察 livedata 的正确方法是啥？调用观察者方法失败
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【中文标题】在 xml 中设置/观察 livedata 的正确方法是啥？调用观察者方法失败【英文标题】：what is the Correct way to set/observe livedata in xml ? Failed to call observer method在 xml 中设置/观察 livedata 的正确方法是什么？调用观察者方法失败 【发布时间】：2022-01-10 20:54:12 【问题描述】：我正在尝试将 LiveData 直接绑定到 xml。
代码正在编译.. 但是在运行时当我输入这个片段时，我收到了这个错误
我不知道这个错误是什么意思..
2021-12-05 11:43:00.759 8215-8215/com.example.fragmentnavigation E/androidRuntime: FATAL EXCEPTION: main
Process: com.example.fragmentnavigation, PID: 8215
java.lang.RuntimeException: Failed to call observer method
at androidx.lifecycle.ClassesInfoCache$MethodReference.invokeCallback(ClassesInfoCache.java:232)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeMethodsForEvent(ClassesInfoCache.java:199)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeCallbacks(ClassesInfoCache.java:190)
at androidx.lifecycle.ReflectiveGenericLifecycleObserver.onStateChanged(ReflectiveGenericLifecycleObserver.java:40)
at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:354)
at androidx.lifecycle.LifecycleRegistry.forwardPass(LifecycleRegistry.java:265)
at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.java:307)
at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.java:148)
at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.java:134)
at androidx.fragment.app.FragmentViewLifecycleOwner.handleLifecycleEvent(FragmentViewLifecycleOwner.java:88)
at androidx.fragment.app.Fragment.performStart(Fragment.java:3028)
at androidx.fragment.app.FragmentStateManager.start(FragmentStateManager.java:589)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:300)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:524)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: android.content.res.Resources$NotFoundException: String resource ID #0x1
at android.content.res.Resources.getText(Resources.java:444)
at android.widget.TextView.setText(TextView.java:6412)
at com.example.fragmentnavigation.databinding.FragmentCheckoutBindingImpl.executeBindings(FragmentCheckoutBindingImpl.java:246)
at androidx.databinding.ViewDataBinding.executeBindingsInternal(ViewDataBinding.java:512)
at androidx.databinding.ViewDataBinding.executePendingBindings(ViewDataBinding.java:484)
at androidx.databinding.ViewDataBinding$OnStartListener.onStart(ViewDataBinding.java:1706)
at java.lang.reflect.Method.invoke(Native Method)
at androidx.lifecycle.ClassesInfoCache$MethodReference.invokeCallback(ClassesInfoCache.java:222)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeMethodsForEvent(ClassesInfoCache.java:199)
at androidx.lifecycle.ClassesInfoCache$CallbackInfo.invokeCallbacks(ClassesInfoCache.java:190)
at androidx.lifecycle.ReflectiveGenericLifecycleObserver.onStateChanged(ReflectiveGenericLifecycleObserver.java:40)
at androidx.lifecycle.LifecycleRegistry$ObserverWithState.dispatchEvent(LifecycleRegistry.java:354)
at androidx.lifecycle.LifecycleRegistry.forwardPass(LifecycleRegistry.java:265)
at androidx.lifecycle.LifecycleRegistry.sync(LifecycleRegistry.java:307)
at androidx.lifecycle.LifecycleRegistry.moveToState(LifecycleRegistry.java:148)
at androidx.lifecycle.LifecycleRegistry.handleLifecycleEvent(LifecycleRegistry.java:134)
at androidx.fragment.app.FragmentViewLifecycleOwner.handleLifecycleEvent(FragmentViewLifecycleOwner.java:88)
at androidx.fragment.app.Fragment.performStart(Fragment.java:3028)
at androidx.fragment.app.FragmentStateManager.start(FragmentStateManager.java:589)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:300)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002)
at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:524)
at android.os.Handler.handleCallback(Handler.java:938)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
这是我的 ViewModel 类
package com.example.fragmentnavigation.vm
import androidx.lifecycle.LiveData
import androidx.lifecycle.MutableLiveData
import com.example.fragmentnavigation.products
import androidx.lifecycle.ViewModel
import com.example.fragmentnavigation.Product
class CheckoutViewModel(id:Int, quantity:Int): ViewModel()
private val noice = products.find it.id == id
private val _product = MutableLiveData<Product>(noice)
private val _product_name = MutableLiveData<String>(noice?.name)
private val _product_price = MutableLiveData<Float>(noice?.price)
private val _product_shortDescription = MutableLiveData<String>(noice?.shortDescription)
private val _product_longDescription = MutableLiveData<String>(noice?.longDescription)
private var _qty = MutableLiveData(quantity)
val product:LiveData<Product>
get() = _product
val product_name:LiveData<String>
get() = _product_name
val product_price: LiveData<Float>
get() = _product_price
val product_short_desription:LiveData<String>
get() = _product_shortDescription
val product_long_desription:LiveData<String>
get() = _product_longDescription
val product_image_id:Int?
get() = _product.value?.imageId
val order_total_price:String
get() = "Order Total: " + ((_product.value?.price)?.times(qty)) .toString()
val qty:LiveData<Int>
get() = _qty
fun addQty(quantity:Int)
_qty.value?.let
_qty.value = it + quantity
fun decrQty(quantity: Int)
_qty.value?.let
if(quantity - it > 0)
_qty.value = it - quantity
private fun Float?.times(qty: LiveData<Int>): Float?
return this?.let qty.value?.times(it)
这是我的片段布局
<?xml version="1.0" encoding="utf-8"?>
<layout>
<data>
<variable
name="viewmodel"
type="com.example.fragmentnavigation.vm.CheckoutViewModel" />
</data>
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_
android:layout_
tools:context=".CheckoutFragment">
<TextView
android:id="@+id/shopping_cart"
android:layout_
android:layout_
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
android:text="@string/shopping_cart"
android:textSize="30sp"
android:textStyle="bold"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toTopOf="parent" />
<ImageView
android:id="@+id/product_image"
android:layout_
android:layout_
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:contentDescription="@string/product_image"
android:src="@drawable/pixel3"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/shopping_cart" />
<TextView
android:id="@+id/product_price"
android:layout_
android:layout_
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintHorizontal_bias="0.0"
app:layout_constraintStart_toEndOf="@+id/product_image"
app:layout_constraintTop_toBottomOf="@+id/product_name"
android:text="@String.valueOf(viewmodel.product_price)"
tools:text="Price: Rs 65000" />
<TextView
android:id="@+id/product_name"
android:layout_
android:layout_
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
android:layout_marginEnd="16dp"
android:layout_marginRight="16dp"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toEndOf="@+id/product_image"
app:layout_constraintTop_toBottomOf="@+id/shopping_cart"
android:text="@viewmodel.product.name"
tools:text="PIXEL 3a"/>
<TextView
android:id="@+id/product_quantity"
android:layout_
android:layout_
android:layout_marginStart="16dp"
android:layout_marginLeft="16dp"
android:layout_marginTop="16dp"
app:layout_constraintStart_toEndOf="@+id/product_image"
app:layout_constraintTop_toBottomOf="@+id/product_price"
android:text="@viewmodel.qty"
tools:text="Qty: 1"/>
<TextView
android:id="@+id/order_total"
android:layout_
android:layout_
android:layout_marginTop="24dp"
android:textSize="24sp"
android:textStyle="bold"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="@+id/product_quantity"
android:text="@String.valueOf(viewmodel.product_price)"
tools:text="@string/order_total" />
<Button
android:id="@+id/checkout"
android:layout_
android:layout_
android:layout_marginTop="16dp"
android:text="@string/checkout"
app:layout_constraintEnd_toEndOf="@+id/order_total"
app:layout_constraintStart_toStartOf="@+id/order_total"
app:layout_constraintTop_toBottomOf="@+id/order_total" />
<Button
android:id="@+id/add_btn"
android:layout_
android:layout_
android:layout_marginVertical="8dp"
android:text="+"
android:onClick="@()-> viewmodel.addQty(1)"
app:layout_constraintBottom_toTopOf="@+id/order_total"
app:layout_constraintEnd_toEndOf="@+id/product_price"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toEndOf="@+id/del_btn"
app:layout_constraintTop_toBottomOf="@+id/product_price" />
<Button
android:id="@+id/del_btn"
android:layout_
android:layout_
android:layout_marginVertical="8dp"
android:text="-"
android:onClick="@()-> viewmodel.decrQty(1)"
app:layout_constraintBottom_toTopOf="@+id/order_total"
app:layout_constraintEnd_toStartOf="@+id/add_btn"
app:layout_constraintHorizontal_bias="0.5"
app:layout_constraintStart_toEndOf="@+id/checkout"
app:layout_constraintTop_toBottomOf="@+id/product_price" />
</androidx.constraintlayout.widget.ConstraintLayout>
</layout>
这是我的片段类
package com.example.fragmentnavigation
import android.annotation.SuppressLint
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import android.view.ViewGroup
import androidx.databinding.DataBindingUtil
import androidx.fragment.app.Fragment
import androidx.lifecycle.Observer
import androidx.lifecycle.ViewModelProvider
import androidx.navigation.fragment.findNavController
import com.example.fragmentnavigation.databinding.FragmentCheckoutBinding
import com.example.fragmentnavigation.vm.CheckoutVMFactory
import com.example.fragmentnavigation.vm.CheckoutViewModel
import kotlinx.android.synthetic.main.fragment_checkout.*
class CheckoutFragment : Fragment()
lateinit var bind: FragmentCheckoutBinding
lateinit var vm : CheckoutViewModel
override fun onCreate(savedInstanceState: Bundle?)
super.onCreate(savedInstanceState)
val id = CheckoutFragmentArgs.fromBundle(requireArguments()).id
val vmFactory = CheckoutVMFactory(id,1)
vm = ViewModelProvider(viewModelStore,vmFactory).get(CheckoutViewModel::class.java)
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
): View?
// Inflate the layout for this fragment
bind = DataBindingUtil.inflate(inflater,R.layout.fragment_checkout,container,false)
bind.viewmodel = vm
bind.lifecycleOwner = viewLifecycleOwner
return bind.root
override fun onViewCreated(view: View, savedInstanceState: Bundle?)
vm.product.observe(viewLifecycleOwner,
setData(it)
)
fun setData(noi_product : Product)
with(noi_product)
product_image.setImageResource(imageId)
checkout.setOnClickListener
findNavController().navigate(CheckoutFragmentDirections.actionCheckoutToThanks(this.id))
如果您需要任何其他数据来诊断问题，请询问我
【问题讨论】：
为什么要使用实时数据，为什么不直接使用ObservableField<Type>？
我不熟悉 [ObservableField我在 Youtube 上看另一个教程时想出了答案
所以当您尝试将“非字符串”数据绑定到 textView 中的文本属性时，基本上会发生这种类型的错误
解决这个问题的方法是对您要在 xml 布局中使用的所有非字符串数据类型使用“String.valueOf()”
例如：-
android:text = " @ String.valueOf( //code ) "
如果您想连接一些通用文本，请使用 ` //string `（重音标签）
例如：-
android:text = " @ `something` + String.valueOf( //code ) "
【讨论】：
【参考方案2】：把你的 onCreateView 方法改成这个方法
override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?
): View?
// Inflate the layout for this fragment
bind = DataBindingUtil.inflate(inflater,R.layout.fragment_checkout,container,false)
bind.viewmodel = vm
bind.lifecycleOwner = viewLifecycleOwner
bind.executePendingBindings()
return bind.root
【讨论】：
.executePendingBindings() 有什么作用？ "评估挂起的绑定，更新任何将表达式绑定到已修改变量的视图。"以上是关于在 xml 中设置/观察 livedata 的正确方法是啥？调用观察者方法失败的主要内容，如果未能解决你的问题，请参考以下文章
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