custom annotation for validation

validation using custom annotation

class MainActivity : AppCompatActivity(), ConstraintValidatorContext {

    lateinit var edt: EditText
    lateinit var btn: Button

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        edt = findViewById(R.id.edt)
        btn = findViewById(R.id.btn)

        btn.setOnClickListener {
            val eighteenOrOlderValidator = EighteenOrOlderValidator()
            val eighteenOrOlder = EighteenOrOlder()
            if (eighteenOrOlderValidator.isValid(edt.text.toString(), this)) {
                Toast.makeText(this, "hurray", Toast.LENGTH_SHORT).show()
            } else {
                Toast.makeText(this, eighteenOrOlder.message, Toast.LENGTH_SHORT).show()
            }
        }
    }

    override fun disableDefaultConstraintViolation() {

    }

    override fun getDefaultConstraintMessageTemplate(): String {
        return ""
    }

    override fun buildConstraintViolationWithTemplate(messageTemplate: String?): ConstraintValidatorContext.ConstraintViolationBuilder? {
        return null
    }
}

@Target(AnnotationTarget.FIELD)
@Retention(AnnotationRetention.RUNTIME)
@Constraint(validatedBy = [EighteenOrOlderValidator::class])
annotation class EighteenOrOlder(
    val message: String = "validation message here",
    val group: Array<KClass<*>> = [],
    val payload: Array<KClass<out Payload>> = []
)

class EighteenOrOlderValidator : ConstraintValidator<EighteenOrOlder, String> {
    override fun isValid(value: String?, context: ConstraintValidatorContext?): Boolean {
        return value?.length!! >= 5
    }

    override fun initialize(constraintAnnotation: EighteenOrOlder?) {

    }

}