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generics - 使用泛型类型设计类和接口

问题描述

我有以下接口映射并接受作为参数 aInsectTypesEntity并返回 a 的对象和返回 a 的InsectDataModel另一个对象List<InsectDataModel>

我正在尝试使用泛型来做到这一点，因为我想练习这个。

interface InsectInteractorMapper<T> {
    fun map(insectTypesEntity: T): T
    fun map(cursor: Cursor): List<T>
}

如果没有泛型，它将是这样的：

interface InsectInteractorMapper<InsectTypesEntity> {
    fun map(insectTypesEntity: InsectTypesEntity): InsectDataModel
    fun map(cursor: Cursor): List<InsectDataModel>
}

我试图让我的类使用接口的通用版本实现这一点，但是，我得到了许多相关的错误：

1) Return type is 'insectDataModel' which is not a subtype of overridden
public abstract fun map(insectTypesEntity: InsectTypesEntity): InsectTypeEntity defined in InsectInteractorMapper

2) Return type is 'List<InsectDataModel>' which is not a subtype of overridden
public abstract fun map(cursor: Cursor): List<InsectTypesEntity> defined in InsectInteractorMapper

实现接口的类

class InsectInteractorMapperImp: InsectInteractorMapper<InsectTypesEntity> {
    override fun map(insectTypesEntity: InsectTypesEntity): InsectDataModel {

        return InsectDataModel(
                insectTypesEntity.friendlyName,
                insectTypesEntity.scientificName,
                insectTypesEntity.classification,
                insectTypesEntity.imageAsset,
                insectTypesEntity.dangerLevel)
    }

    override fun map(cursor: Cursor): List<InsectDataModel> {
        val insectDataModelList: MutableList<InsectDataModel> = mutableListOf()

        cursor.moveToFirst()
        while(cursor.moveToNext()) {
            InsectDataModel().let {
                it.friendlyName = cursor.getString(cursor.getColumnIndexOrThrow(InsectContract.COLUMN_FRIENDLY_NAME))
                it.scientificName = cursor.getString(cursor.getColumnIndexOrThrow(InsectContract.COLUMN_SCIENTIFIC_NAME))
                it.dangerLevel = cursor.getInt(cursor.getColumnIndexOrThrow(InsectContract.COLUMN_DANGER_LEVEL))

                insectDataModelList.add(it)
            }
        }

        cursor.close()
        return insectDataModelList.toList()
    }
}

使用泛型正常工作的最佳方法是什么？

非常感谢您的任何建议，

==== UPDATE 修改了输入/输出差异的接口：

interface InsectInteractorMapper<in E, out M> {
    fun map(insectTypesEntity: E): M
    fun map(cursor: Cursor): List<M>
}

但是，当我尝试使用界面时收到警告：

unchecked assignment java.util.List to java.util.List<InsectDataModel> Reason insectDataModelMapper has raw type so result of map will be erased

当我这样使用它时：

insectInteractorMapper = new InsectInteractorMapperImp();
insectDataModelList = insectInteractorMapper.map(cursor);

标签： genericsinterfacekotlin

解决方案

既然你想要一个in类型和一个out类型，你需要像这样声明它们：

interface InsectInteractorMapper<in T1, out T2> {
    fun map(insectTypesEntity: T1): T2
    fun map(cursor: Cursor): List<T2>
}

然后你的代码就可以工作了

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