generics - 使用泛型类型设计类和接口(interface)

Question

我有以下接口(interface)映射和接受作为参数的InsectTypesEntity并返回 InsectDataModel 的对象另一个返回 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，它会是这样的:

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(interface)的通用版本来实现这一点，但是，我得到了很多相关的错误:

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(interface)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()
    }
}

使用泛型使其正常工作的最佳方法是什么？

非常感谢您的任何建议，

==== 更新输入/输出差异的修改界面:

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);

Answer 1

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>
}

那么你的代码就可以工作了