java Kotlin 中的 Enum.valueOf
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Enum.valueOf in Kotlin
提问by AndroidEx
Is there a way to make something like this work in Kotlin without the reflection?
有没有办法在没有反射的情况下在 Kotlin 中做这样的事情？
inline fun <reified T : kotlin.Enum<T>> safeValueOf(type: String?): T? {
return java.lang.Enum.valueOf(T::class.java, type)
}
The example below doesn't compile due to:
以下示例无法编译，原因如下：
Type parameter bound for T in
inline fun <reified T : kotlin.Enum<T>> safeValueOf(type: kotlin.String?): T?is not satisfied: inferred typeTestEnum?is not a subtype ofkotlin.Enum<TestEnum?>
inline fun <reified T : kotlin.Enum<T>> safeValueOf(type: kotlin.String?): T?不满足为 T in 绑定的类型参数：推断类型TestEnum?不是的子类型kotlin.Enum<TestEnum?>
enum class TestEnum
fun main() {
val value: TestEnum? = safeValueOf("test")
}
采纳答案by yole
Your function works if you specify the type parameter value explicitly:
如果您明确指定类型参数值，您的函数将起作用：
val value = safeValueOf<TestEnum>("test")
The original code is supposed to work as well, but doesn't work because of a bug in the type inference implementation: https://youtrack.jetbrains.com/issue/KT-11218
原始代码应该也能工作，但由于类型推断实现中的错误而无法工作：https: //youtrack.jetbrains.com/issue/KT-11218
回答by Peter
Since Kotlin 1.1, it's possible to access the constants in an enum class in a generic way, using the enumValues() and enumValueOf() functions:
从 Kotlin 1.1 开始，可以使用 enumValues() 和 enumValueOf() 函数以通用方式访问枚举类中的常量：
enum class RGB { RED, GREEN, BLUE }
inline fun <reified T : Enum<T>> printAllValues() {
print(enumValues<T>().joinToString { it.name })
}
printAllValues<RGB>() // prints RED, GREEN, BLUE
https://kotlinlang.org/docs/reference/enum-classes.html#working-with-enum-constants
https://kotlinlang.org/docs/reference/enum-classes.html#working-with-enum-constants
回答by Gibolt
Crash-safe Solution
碰撞安全解决方案
Create an extension and then call valueOf<MyEnum>("value"). If the type is invalid, you'll get null and have to handle it
创建一个分机，然后调用valueOf<MyEnum>("value"). 如果类型无效，您将获得 null 并且必须处理它
inline fun <reified T : Enum<T>> valueOf(type: String): T? {
return try {
java.lang.Enum.valueOf(T::class.java, type)
} catch (e: IllegalArgumentException) {
null
}
}
Alternatively, you can set a default value, calling valueOf<MyEnum>("value", MyEnum.FALLBACK), and avoiding a null response. You can extend your specific enum to have the default be automatic
或者，您可以设置默认值，调用valueOf<MyEnum>("value", MyEnum.FALLBACK)并避免空响应。您可以扩展您的特定枚举以将默认值设为自动
inline fun <reified T : Enum<T>> valueOf(type: String, default: T): T {
return try {
java.lang.Enum.valueOf(T::class.java, type)
} catch (e: IllegalArgumentException) {
default
}
}
Or if you want both, make the second:
或者，如果您想要两者，请制作第二个：
inline fun <reified T : Enum<T>> valueOf(type: String, default: T): T = valueOf<T>(type) ?: default
