从注释中获取值失败

Question

这是注释定义：

@Target(AnnotationTarget.PROPERTY)
@Retention(AnnotationRetention.RUNTIME)
@MustBeDocumented
annotation class MyAnno(val desc: String, val comment: String) { }

以下是MyAnno使用的地方：

class MyAnnoUser {
    @MyAnno(desc = "name", comment = "name comment")
    lateinit var name: String

    @MyAnno(desc = "age", comment = "age comment")
    var age: Int = 0

    @MyAnno(desc =  "money", comment = "money comment")
    var money: Double = 0.0

    @MyAnno(desc =  "gender", comment = "gender comment")
    var gender: Boolean = false

    override fun toString(): String {
        return "(name: $name; age: $age; money: $money; gender: ${if (gender) "men" else "women"})"
    }
}

这是在MyAnno中读取值的代码：

class MyAnnoExpression(val obj: Any, val context: Context) {

    val numTypeSet = setOf("Int", "Double", "Byte")

    fun expression() {

        val clazz = obj::class

        clazz.declaredMemberProperties.forEach { prop ->
            val mutableProp = try {
                prop as KMutableProperty<*>
            } catch (e: Exception) {
                null
            } ?: return@forEach

            val desc = mutableProp.findAnnotation<MyAnno>()
            desc?.let {
                val propClassName = mutableProp.returnType.toString().removePrefix("kotlin.")
                when (propClassName) {
                    in numTypeSet -> mutableProp.setter.call(obj, (readProp(it, context) as kotlin.String).toNum(propClassName))
                    "String" -> mutableProp.setter.call(obj, (readProp(it, context) as kotlin.String))
                    "Boolean" -> mutableProp.setter.call(obj, (readProp(it, context) as kotlin.String).toBoolean())
                }
            }
        }
    }

    private fun readProp(value: MyAnno, context: Context): Any? {
        val prop = Properties()
        val input = context.assets.open("app.properties")
        prop.load(InputStreamReader(input, "utf-8"))
        return prop.get(value.desc)
    }
}

现在调试器向我展示了value函数中readProp(...)的以下信息：

@com.demo.basekotlin.MyAnno(comment=age comment, desc=age)

但是当我从desc阅读value时我得到了例外：

An exception occurs during Evaluate Expression Action : org.jetbrains.eval4j.VOID_VALUE cannot be cast to org.jetbrains.eval4j.AbstractValue

我的代码中找不到任何错误，是否需要另外的程序设置？

Answer 1

据我了解，您只想查看给定属性的注释值。

首先，让我们声明一个注释。

@Target(PROPERTY)
@Retention(AnnotationRetention.RUNTIME)
annotation class PropertyAnnotation(val desc: String)

容器：

class Container {

    @PropertyAnnotation("Name")
    var name: String? = null

    @PropertyAnnotation("Age")
    var age: Int = -1

    var notAnnotatedProperty: String = "not annotated"
}

最后，代码负责获取所有声明的属性，然后找到一个注释为PropertyAnnotation的属性，将其强制转换为它，并从中获取值。

fun main() {

    val container = Container()

    container::class.declaredMemberProperties.forEach { property ->
        (property.annotations.find {
            it is PropertyAnnotation
        } as? PropertyAnnotation)?.let {
            println("Property: `$property` is ${it.desc}")
        }
    }

}

输出：

Property: `var Container.age: kotlin.Int` is Age
Property: `var Container.name: kotlin.String?` is Name

善良的丑陋。但是，让我们使用更多的Kotlin pro-dev功能。

让我们为任何非null类型创建扩展函数，它返回给定类型的所有成员属性：

inline fun <reified T : Any> Any.getMemberProperty(): List<T> {
    return this::class.declaredMemberProperties.mapNotNull { prop ->
        (prop.annotations.find { ann -> ann is T }) as? T
    }
}

现在用法：

fun main() {

    val container = Container()

    container.getMemberProperty<PropertyAnnotation>().forEach {
        println(it.desc)
    }
}