Question

我的接口定义如下：

interface OnItemClickDelegate<T: Entity> {
    fun onItemClick(entity: T?)
}

现在，我在另一个类中匿名定义了接口：

var itemClickDelegate = object : OnItemClickDelegate<Derived> {
        override fun onItemClick(entity: Derived?) {
            doSomethingWith(entity)
        }
    }

这可以很好地编译，但是当我切换到：

var itemClickDelegate = OnItemClickDelegate<Derived> { entity -> doSomethingWith(entity) }

我收到一个编译器错误，提示：

Interface OnItemClickDelegate does not have constructors

如何用简短的注释写我的声明？

Answer 1

可悲的是，对于Kotlin接口，Kotlin不支持该语法，仅支持Java（无论是否使用泛型）。

您可以执行以下操作：


[
 {
    "mca_sub1":1.1,
    "mca_sub2":2.8,
            "bca_sub1":1.1,
            "bca_sub2":2.8  
 },
 {
    "mca_sub1":1.15,
    "mca_sub2":1.18,
            "bca_sub1":1.15,
            "bca_sub2":1.18 
 },
 {
    "mca_sub1":1.2,
    "mca_sub2":1.9,
            "bca_sub1":1.2,
            "bca_sub2":1.9  
 }
]

这样，您可以像这样实例化侦听器：


interface OnItemClickDelegate<T : Entity> {
    fun onItemClick(entity: T?)

    companion object {
        inline operator fun <T : Entity> invoke(crossinline op: (entity: T?) -> Unit) =
            object : OnItemClickDelegate<T> {
                override fun onItemClick(entity: T?) = op(entity)
            }
    }
}

Answer 2

从 Kotlin 1.4 开始，只需在接口声明前添加 fun 即可，如下所示：

fun interface OnItemClickDelegate<T : Entity> {
    fun onItemClick(entity: T?)
}

https://kotlinlang.org/docs/whatsnew14.html#sam-conversions-for-kotlin-interfaces

SAM与泛型转换

2 个答案: