Create custom Annotation using Kotlin — tutorial


  1. BkThread — the annotation declaration
  2. AnnotationUtility.kt — The helper class that checks for the thread and generates a warning.
  3. ClassA.kt — the class which have the annotated methods
  4. MainActivity .kt — calls the method in UI thread which generates a warning and then calls from a background thread shows no warning.


package com.example.testcustomannotation@Target(AnnotationTarget.FUNCTION)
annotation class BkThread{


package com.example.testcustomannotationimport android.os.Looper
import android.util.Log
import java.lang.Exception
import java.lang.reflect.Method
class AnnotationUtility { companion object{fun checkThreadWarnings(method: Method?){
if (method != null) {
try {
val bkThreadAnnotation =
val annotation = method.getAnnotation(bkThreadAnnotation)

if (annotation != null && Looper.myLooper() == Looper.getMainLooper()) {
Log.d("WARNING"," should be called from a background thread.")
}catch (e: Exception){
Log.d("Exception", e.toString())


package com.example.testcustomannotationclass ClassA { // A class in your own framework.    @BkThread
fun operation1() {
// do something


package com.example.testcustomannotationimport
import android.os.Bundle
import org.jetbrains.anko.doAsync
class MainActivity : AppCompatActivity() { override fun onCreate(savedInstanceState: Bundle?) {
val obj = ClassA()
obj.operation1() // Will generate Warning.
doAsync {
obj.operation1() // called righly, no warning
implementation 'org.jetbrains.anko:anko-common:0.9'


2020-04-03 20:44:21.194 6342-6342/com.example.testcustomannotation D/WARNING: operation1 should be called from a background thread.




works @Twin Health

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Ankur Srivastava

Ankur Srivastava

works @Twin Health

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