Kotlin Annotation：获取接口内部带注释的属性

Question

Overview

I'm trying to build my first annotation processor and it's going pretty well. I am creating a code generating processor that basically generates SharedPreferences for a defined interface. My current annotations are SharedPrefs and Default . @SharedPrefs informs the processor that the file is an interface and needs a generated prefs file. @Default is what I annotated some properties in the interface as in order to let the processor know what to set the default value to. There can be multiple files defined as @SharedPrefs .

Implementation

I currently use the following code to get a list of files annotated with @SharedPrefs and the @Default s:

roundEnv.getElementsAnnotatedWith(SharedPrefs::class.java)?.forEach { element ->
  ...
  roundEnv.getElementsAnnotatedWith(Default::class.java)?.forEach {
    ...
  }
}

@SharedPrefs :

@Retention(AnnotationRetention.SOURCE)
@Target(AnnotationTarget.CLASS)
annotation class SharedPrefs(val showTraces: Boolean = false)

@Default :

@Retention(AnnotationRetention.SOURCE)
@Target(AnnotationTarget.PROPERTY)
annotation class Default(val defaultValue: String = "[null]")

In Use:

@SharedPrefs
interface InstanceSettings {
    var wifiPassword: String
    @Default("20")
    var count: Int
}

Problem

As is, the inner forEach is returning all properties from all files annotated with @Default . The code generation works fine, but this doesn't seem like the best way forward. Is there a way to get just the properties w/in the current @SharedPrefs class that I'm processing? For instance, something like:

roundEnv.getElementsAnnotatedWith(SharedPrefs::class.java)?.forEach { element ->
  ...
  element.methodToGetAnnotatedProperties(Default::class.java)?.forEach {
    ...
  }
}

* EDIT *

I found that, for methods that I annotate

@SomeAnnotation
fun someMethod()

I can loop through the element.enclosingElements and find if it has an annotation using enclosingElement.getAnnotation(<SomeAnnotation::class.java>) . Unfortunately, and correct me if I'm wrong here, I can't annotate interface variables with an annotation with AnnotationTarget.FIELD since they don't have a backing field since it's an interface and they're not implemented. Therefore, I'm using AnnotationTarget.PROPERTY . When looping through the enclosing elements, all of the variables show up as getters and setters. For the example above for InstanceSettings , I get getWifiPassword , setWifiPassword , getCount and setCount . I do not get an element for just wifiPassword or count . Calling getAnnotation(Default::class.java) will always return null on these since they are generated.

Also, any other resources on annotation processing that anyone knows of would be a great addition in the comments. Thanks!

Answer 1

Similar question in java was asked here

Here is how you can create an extension function which will do job for you!

roundEnv.getElementsAnnotatedWith(SharedPrefs::class.java)?.forEach { element ->
    ...
    roundEnv.findNestedElements(SharedPrefs::class, Default::class)?.forEach {
        ...
    }
}

fun <T> RoundEnvironment.findNestedElements(parent: KClass<*>, child: KClass<T>): List<Element>? {
    val childs = this.getElementsAnnotatedWith(child.java)
    val list = ArrayList<Element>()
    for (element in childs)
    {
        if (element.getEnclosingElement().getAnnotation(parent.java) != null)
        {
            list.add(element)
        }
    }
    return if(list.isEmpty()) null else list
}

Answer 2

So I think I've found the solution:

For the example of InterfaceSettings :

@SharedPrefs
interface InstanceSettings {
    var wifiPassword: String
    @Default("20")
    var count: Int
}

The simplified generated Java code is :

public interface InstanceSettings {
   @NotNull
   String getWifiPassword();

   void setWifiPassword(@NotNull String var1);

   int getCount();

   void setCount(int var1);

   public static final class DefaultImpls {
      public static void count$annotations() {
      }
   }
}

The element returned when calling roundEnv.getElementsAnnotatedWith(Default::class.java) is count$annotations . So when I call getEnclosingElement() , DefaultImpls is returned. If I call getEnclosingElement() again , InstanceSettings is returned. I actually call getSimpleName() on that result and compare it with the className from the item annotated with @SharedPrefs to see if it is a child:

roundEnv.getElementsAnnotatedWith(SharedPrefs::class.java)?.forEach { element ->
  val className = element.simpleName.toString()
  val defaults = roundEnv.getElementsAnnotatedWith(Default::class.java)?.filter {
    // it.enclosingElement -> DefaultImpls
    // DefaultImpls.enclosingElement -> com.mypackage.InstanceSettings
    it.enclosingElement.enclosingElement.simpleName == className
  }
}