Get value from annotation failed - kotlin

Question

This is annotation definition:
#Target(AnnotationTarget.PROPERTY)
#Retention(AnnotationRetention.RUNTIME)
#MustBeDocumented
annotation class MyAnno(val desc: String, val comment: String) { }
And below is where the MyAnno used:
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"})"
}
}
Here's code to read the value in MyAnno:
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)
}
}
Now the Debugger shows me following info of value in readProp(...) function:
#com.demo.basekotlin.MyAnno(comment=age comment, desc=age)
But i got exception when read desc from value:
An exception occurs during Evaluate Expression Action : org.jetbrains.eval4j.VOID_VALUE cannot be cast to org.jetbrains.eval4j.AbstractValue
I can't find any thing wrong in my code, is there another program setting needed?

Answer 1

As I understand you just want to see annotation value for given property.
First, let's declare an annotation.
#Target(PROPERTY)
#Retention(AnnotationRetention.RUNTIME)
annotation class PropertyAnnotation(val desc: String)
Container:
class Container {
#PropertyAnnotation("Name")
var name: String? = null
#PropertyAnnotation("Age")
var age: Int = -1
var notAnnotatedProperty: String = "not annotated"
}
And finally, code responsible for get all declared properties, then find a properties annotated as PropertyAnnotation, cast it to it, and get value from it.
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}")
}
}
}
Output:
Property: `var Container.age: kotlin.Int` is Age
Property: `var Container.name: kotlin.String?` is Name
Kind ugly. But, let's use more Kotlin pro-dev-features.
Let's create extension function for any not-null type which returns all member property of given type:
inline fun <reified T : Any> Any.getMemberProperty(): List<T> {
return this::class.declaredMemberProperties.mapNotNull { prop ->
(prop.annotations.find { ann -> ann is T }) as? T
}
}
And now usage:
fun main() {
val container = Container()
container.getMemberProperty<PropertyAnnotation>().forEach {
println(it.desc)
}
}