传递 lambda 而不是接口 [英] Passing lambda instead of interface
问题描述
我创建了一个界面:
interface ProgressListener {
fun transferred(bytesUploaded: Long)
}
但只能用作匿名类,不能用作 lambda
but can use it only as an anonymous class, not lambda
dataManager.createAndSubmitSendIt(title, message,
object : ProgressListener {
override fun transferred(bytesUploaded: Long) {
System.out.println(bytesUploaded.toString())
}
})
我认为应该可以用 lambda 替换它:
I think it should be a possibility to replace it by lambda:
dataManager.createAndSubmitSendIt(title, message, {System.out.println(it.toString())})
但我收到错误:Type mismatch;必需 - ProgressListener, found - () ->单位?
我做错了什么?
推荐答案
正如@zsmb13 所说,SAM 转换仅支持 Java 接口.
As @zsmb13 said, SAM conversions are only supported for Java interfaces.
你可以创建一个扩展函数来让它工作:
You could create an extension function to make it work though:
// Assuming the type of dataManager is DataManager.
fun DataManager.createAndSubmitSendIt(title: String,
message: String,
progressListener: (Long) -> Unit) {
createAndSubmitSendIt(title, message,
object : ProgressListener {
override fun transferred(bytesUploaded: Long) {
progressListener(bytesUploaded)
}
})
}
Kotlin 1.4 将带来函数接口,为 Kotlin 中定义的接口启用 SAM 转换.这意味着如果您使用 fun
关键字定义接口,则可以使用 lambda 调用您的函数.像这样:
Kotlin 1.4 will bring function interfaces that enables SAM conversions for interfaces defined in Kotlin. This means that you can call your function with a lambda if you define your interface with the fun
keyword. Like this:
fun interface ProgressListener {
fun transferred(bytesUploaded: Long)
}
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