如何为Spinner编写一个绑定适配器，以接收LiveData作为输入? [英] how to write a binding adapter for spinner which receives LiveData as input?

问题描述

我在xml中定义了一个微调框，

i have a spinner defined in the xml like this

<Spinner
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:id="@+id/expense_category"
        app:sourceData="@{()->createExpenseViewModel.getAllSourceItems(1)}"
        app:layout_constraintStart_toStartOf="@+id/textView"
        android:layout_marginTop="20dp"
        app:layout_constraintTop_toBottomOf="@+id/textView" app:layout_constraintWidth_percent="0.7"
/>

createExpenseViewModel.getAllSourceItems(1)此方法返回LiveData< List< Source >>，因此我已经为这种情况编写了绑定适配器

createExpenseViewModel.getAllSourceItems(1) this method returns LiveData <List<Source>>, so i have written a binding adapter for that case

@BindingAdapter("app:sourceData")
fun setSourceData(spinner: Spinner, sourceList: List<Source>) {

    val categoryItems = ArrayList<String>()
    categoryItems.addAll(sourceList.map { it.sourceName })
    val spinnerAdapter =
        ArrayAdapter<String>(spinner.context, R.layout.simple_spinner_dropdown_item, categoryItems)
    spinner.adapter = spinnerAdapter


}

在构建应用程序时，出现以下错误， ****/ data binding error ****msg:Cannot find the proper callback class for app:sourceData. Tried java.util.List but it has 25 abstract methods, should have 1 abstract methods. file:/home/naveen/Desktop/project-expense/app/src/main/res/layout/activity_create_expense.xml loc:94:34 - 94:80 ****\ data binding error ** **

when building the app, i am getting the following error, ****/ data binding error ****msg:Cannot find the proper callback class for app:sourceData. Tried java.util.List but it has 25 abstract methods, should have 1 abstract methods. file:/home/naveen/Desktop/project-expense/app/src/main/res/layout/activity_create_expense.xml loc:94:34 - 94:80 ****\ data binding error ****

此错误实际上是什么意思，如何解决此错误?

what does this error actually mean,how to resolve this error?

我打算做的是获取实时数据返回的列表并将其转换为ArrayList类型，一旦实时数据返回列表，我就需要触发绑定适配器，但是如果我使用此应用程序:sourceData ="@ {createExpenseViewModel .getAllSourceItems(1)}"并设置绑定适配器，该适配器仅获取空列表

what i intend to do is get the list returned by live data and convert to type ArrayList , i need my binding adapter to be triggered once the livedata returns the list, but if i use this app:sourceData="@{createExpenseViewModel.getAllSourceItems(1)}" and set the binding adapter, the adapter get only null list

推荐答案

我遵循了@muetzenflo建议的核心思想，我在这样的视图模型上创建了一个属性

I have followed the core idea of what @muetzenflo suggested, i have created a property on view model like this

class MainViewModel @Inject constructor(

    val expenseSourceItems:LiveData<List<Source>> = getAllSourceItems(1)

        fun getAllSourceItems(sourceType:Int?): LiveData<List<Source>> {
        val res = sourceRepository.getAllSourceItems(sourceType)
        return res
    }

    // the methods below are omitted for brevity


}

然后我已经使用属性访问语法绑定到微调器

then i have bound to the spinner using property access syntax

<Spinner
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:id="@+id/expense_category"
        app:sourceData="@{createExpenseViewModel.expenseSourceItems}"
        app:layout_constraintStart_toStartOf="@+id/textView"
        android:layout_marginTop="20dp"
        app:layout_constraintTop_toBottomOf="@+id/textView" app:layout_constraintWidth_percent="0.7"
/>

，然后使用相同的绑定适配器

and then used the same binding adapter

@BindingAdapter("app:sourceData")
fun setSourceData(spinner: Spinner, sourceList: List<Source>) {

    val categoryItems = ArrayList<String>()
    categoryItems.addAll(sourceList.map { it.sourceName })
    val spinnerAdapter =
        ArrayAdapter<String>(spinner.context, R.layout.simple_spinner_dropdown_item, categoryItems)
    spinner.adapter = spinnerAdapter


}

对于实时数据，调用数据绑定内部的方法仅适用于诸如onclick之类的回调，并且需要将属性访问用于正常的数据绑定(如填充微调器).

for live data calling a method inside data binding only works for callbacks like onclick, and property access is needed to be used for normal data binding like populating a spinner.

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