如何在LiveData< I>中使用"I"作为已确定类型的参数.班级? [英] How to use 'I' as reified type parameter in a LiveData<I> class?

问题描述

在尝试将LiveData<I> class子类化时，我尝试使用泛型.根据这个答案，我已经尝试过:

I'm trying to use generics when subclassing a LiveData<I> class. According to this answer, I have tried this:

class ItemLiveData<I>(): LiveData<I>() {

    override fun onEvent(querySnapshot: QuerySnapshot?, e: FirebaseFirestoreException?) {
        if (e != null) return

        for (documentChange in querySnapshot!!.documentChanges) {
            when (documentChange.type) {
                DocumentChange.Type.ADDED -> setValue(getItem(documentChange)) //Add to LiveData
            }
        }
    
    private inline fun <reified I> getItem(doc: DocumentChange) = doc.document.toObject<I>(I::class.java)
}

我收到此错误:

Cannot use 'I' as reified type parameter. Use a class instead.

检查此打印屏幕

有人可以帮我吗?

推荐答案

该类的I类型无法进行验证，因此您无法为该函数创建重载的验证化I.我认为您可以通过使类成为构造函数参数来手动调整类类型.像这样:

The class's I type cannot be reified, and so you can't create an overloaded reified I for that function. I think you can manually reify the class type by making the class a constructor parameter. Like this:

class ItemLiveData<I>(private val type: Class<I>): LiveData<I>() {

    override fun onEvent(querySnapshot: QuerySnapshot?, e: FirebaseFirestoreException?) {
        if (e != null) return

        for (documentChange in querySnapshot!!.documentChanges) {
            when (documentChange.type) {
                DocumentChange.Type.ADDED -> setValue(getItem(documentChange)) //Add to LiveData
            }
        }
    
    private fun getItem(doc: DocumentChange) = doc.document.toObject<I>(type)
}

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