关于数据绑定、实时数据和可绘制的问题

Question

我正在尝试将可绘制对象与实时数据数据绑定并遇到此错误

java.lang.RuntimeException: Failed to call observer method
Caused by: android.content.res.Resources$NotFoundException: Resource ID #0x0

我的xml片段（只粘贴了相关部分）

<layout 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">

    <data>
        <import type="androidx.core.content.ContextCompat" />
        <variable name="location" type="String"/>
        <variable name="viewModel"
            type="com.marty.dang.polarpointsweatherapp.presentation.viewmodel.DailyWeatherViewModel"/>
    </data>
        <ImageView
            android:id="@+id/homeFrag_weather_icon"
            android:layout_width="150dp"
            android:layout_height="150dp"
            android:layout_marginTop="40dp"

            android:src="@{ContextCompat.getDrawable(context, viewModel.iconObservable)}"

            app:layout_constraintEnd_toEndOf="parent"
            app:layout_constraintHorizontal_bias="0.497"
            app:layout_constraintStart_toStartOf="parent"
            app:layout_constraintTop_toBottomOf="@+id/homeFrag_title_text_view" />

我的视图模型（只粘贴了相关部分）

val iconObservable: MutableLiveData<Int> by lazy { MutableLiveData<Int>() }

    private fun determineWeatherIcon(weatherDescription: String)  {
        val icon = when(weatherDescription){
            "Thunderstorm" -> R.drawable.thunderstorm_icon
            "Drizzle" -> R.drawable.rain_icon
            "Rain" -> R.drawable.rain_icon
            "Snow" -> R.drawable.snow_icon
            "Clear" -> R.drawable.sun_icon
            "Clouds" -> R.drawable.cloudy_icon
            else -> R.drawable.cloudy_icon
        }

        iconObservable.postValue(icon)
    }

我的可绘制文件夹

但是，如果我只使用常规变量而不是可变的实时数据变量，它就可以正常工作。

var weatherIcon = R.drawable.snow_icon

private fun determineWeatherIcon(weatherDescription: String)  {
    weatherIcon = when(weatherDescription){
        "Thunderstorm" -> R.drawable.thunderstorm_icon
        "Drizzle" -> R.drawable.rain_icon
        "Rain" -> R.drawable.rain_icon
        "Snow" -> R.drawable.snow_icon
        "Clear" -> R.drawable.sun_icon
        "Clouds" -> R.drawable.cloudy_icon
        else -> R.drawable.cloudy_icon
    }
}

android:src="@{ContextCompat.getDrawable(context, viewModel.weatherIcon)}"

任何帮助将不胜感激。谢谢！

Answer 1

您可以在 xml 中使用 app:imageResource 属性：

<layout 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">

    <data>
        <variable name="location" type="String"/>
        <variable name="viewModel" type="com.marty.dang.polarpointsweatherapp.presentation.viewmodel.DailyWeatherViewModel"/>
    </data>
    
    <ImageView
        android:id="@+id/homeFrag_weather_icon"
        app:imageResource="@{viewModel.iconObservable}"
        ... />
...

在您的 viewModel 中，您应该具有以下属性：

val iconObservable: MutableLiveData<Int>

你可以有以下方法：

private fun determineWeatherIcon(weatherDescription: String)  {
    iconObservable.value = when(weatherDescription){
        "Thunderstorm" -> R.drawable.thunderstorm_icon
        "Drizzle" -> R.drawable.rain_icon
        "Rain" -> R.drawable.rain_icon
        "Snow" -> R.drawable.snow_icon
        "Clear" -> R.drawable.sun_icon
        "Clouds" -> R.drawable.cloudy_icon
        else -> R.drawable.cloudy_icon
    }
}

您不需要postValue，除非您在后台线程中设置值。

在您的片段类中，您应该将viewModel 和lifecycleOwner 设置为您的binding：

override fun onCreateView(
    inflater: LayoutInflater,
    container: ViewGroup?,
    savedInstanceState: Bundle?
): View? {
    binding = YourFragmentBinding.inflate(inflater, container, false)
    binding.viewModel = viewModel
    binding.lifecycleOwner = viewLifecycleOwner
    return binding.root
}

Answer 2

iconObservable.value 在你的 xml 上试试这个，它会工作的