I have my own converter from Strings to List
object TypeConverter {
fun stringToListLong(text: String): List<Long> {
val listLong = mutableListOf<Long>()
val listString = text.split(",").map { it.trim() }
listString.forEach {
listLong.add(it.toLong())
}
return listLong
}
}
Then when I try to use it like below it shows the error(Unresolved reference: add)
val someString = "something"
var ids = TypeConverter.stringToListLong(someString)
ids.add(some long value)
Why?
You're returning a List<>, so ids is a List<>, therefore it does not have mutation operations. Make stringToListLong return MutableList<Long>.
Related
I have a top level kotlin object with various constants declared in it. How can I iterate and reflect on those properties/fields?
object Foobar {
val MEANINGFUL_CONSTANT = SomeClass(...)
#JvmStatic
val getConstants: List<SomeClass>
get() {
val props = Foobar::class.staticProperties
return props.mapNotNull { property ->
val p = property.get()
if (p is SomeClass) {
p
} else {
null
}
}
}
}
No matter what I put in for Foobar::class.staticProperties, I get an empty list back. How do I properly reflect on Foobar?
According to the doc of staticProperties
Only properties representing static fields of Java classes are considered static.
That is why staticProperties on Foobar isn't returning anything.
You can use memberProperties and have a condition to match the KType of SomeClass as below. Maybe that helps.
val getConstants: List<Any>
get() {
val props = Foobar::class.memberProperties
val someClassType = SomeClass::class.createType()
return props.mapNotNull { property ->
if (property.returnType == someClassType) {
property.getter.call(this)
} else {
null
}
}
}
Hey I am working in kotlin. I am working on tree data structure. I added the value in list and now I want to find that value and modified their property. But I am getting the error.
VariantNode, StrengthNode, ProductVariant
StrengthNode.kt
class StrengthNode : VariantNode() {
var pricePerUnit: String? = null
var defaultValue = AtomicBoolean(false)
}
ActivityViewModel.kt
class ActivityViewModel : ViewModel() {
var baseNode: VariantNode = VariantNode()
private val defaultValueId = "12643423243324"
init {
createGraph()
}
private fun createGraph() {
val tempHashMap: MutableMap<String, VariantNode> = mutableMapOf()
val sortedList = getSortedList()
sortedList.forEach { productVariant ->
productVariant.strength?.let { strength ->
if (tempHashMap.containsKey("strength_${strength.value}")) {
baseNode.children.contains(VariantNode(strength.value)) // getting error
return#let
}
val tempNode = StrengthNode().apply {
value = strength
pricePerUnit = productVariant.pricePerUnit?.value
if (productVariant.id == defaultValueId) {
defaultValue.compareAndSet(false, true)
}
}
baseNode.children.add(tempNode)
tempHashMap["strength_${strength.value}"] = tempNode
}
productVariant.quantity?.let { quantity ->
if (tempHashMap.containsKey("strength_${productVariant.strength?.value}_quantity_${quantity.value}")) {
return#let
}
val tempNode = QuantityNode().apply {
value = quantity
}
val parent =
tempHashMap["strength_${productVariant.strength?.value}"] ?: baseNode
parent.children.add(tempNode)
tempHashMap["strength_${productVariant.strength?.value}_quantity_${quantity.value}"] =
tempNode
}
productVariant.subscription?.let { subscription ->
val tempNode = SubscriptionNode().apply {
value = subscription
}
val parent =
tempHashMap["strength_${productVariant.strength?.value}_quantity_${productVariant.quantity?.value}"]
?: baseNode
parent.children.add(tempNode)
}
}
baseNode
}
}
I am getting error on this.
I want to find that node value and modified other property.
Your class VariantNode only has a single no-arg constructor, but you're trying to call it with arguments, hence the error
Too many arguments for public constructor VariantNode() defined in com.example.optionsview.VariantNode
Either you have to provide a constructor, that matches your call, e.g.
open class VariantNode(var value: ProductValue?) {
var children: MutableList<VariantNode> = arrayListOf()
}
or you need to adjust your code to use the no-arg constructor instead.
val node = VariantNode()
node.value = strength.value
baseNode.children.contains(node)
Note however, that your call to contains most likely will not work, because you do not provide a custom implementation for equals. This is provided by default, when using a data class.
If you just want to validate whether baseNode.children has any element, where value has the expected value, you can use any instead, e.g.:
baseNode.children.any { it.value == strength.value }
I am learning Kotlin and writing code to check my understanding. I'm trying to use a toString override to print the values of a hashMap that is a property of a class. I can't get it to work. Instead I get output like "kotlin.Unit() -> kotlin.Unit". Also, I don't understand why the values of the hashMap ARE printing out before the toString output. I don't know where that output is coming from. Please help me. Thanks. Below is my code and the output I'm getting.
Code:
package ch07.ExpandoObject
import java.beans.PropertyChangeListener
import java.beans.PropertyChangeSupport
import kotlin.properties.Delegates
import kotlin.reflect.KProperty
class Person(
val name: String = "",
age: Int? = null,
var isMarried: Boolean? = null ,_attributes: kotlin.collections.HashMap<String,String>? = hashMapOf<String, String>()
)
:PropertyChangeAware()
{
var _attributes : kotlin.collections.HashMap<String,String>? = hashMapOf<String, String>()
fun setAttribute(attrName: String, value: String) {
_attributes!!.set(attrName, value)
_attributes!!.set("name", this.name)
}
override fun toString() = "Person(name=\"${name?:""}\", age=${age?:99999}, isMarried=$isMarried) " +
"${_attributes?.get("name")} " + "$name " +
this._attributes!!.forEach { (attrName, value) -> println("$attrName = $value") } +
{
for ((attrName, value) in this._attributes!!) {
println("attribute $attrName = ${this._attributes!![attrName]}")
}
}
val _age = ObservableProperty(propName = "age", propValue = age, changeSupport = changeSupport)
private val observer = {
prop: KProperty<*>, oldValue: Int, newValue: Int ->
changeSupport.firePropertyChange(prop.name, oldValue, newValue)
}
var age: Int by Delegates.observable(initialValue = age?:99999,onChange = observer)
}
class ObservableProperty(val propName: String,
var propValue: Int?, val changeSupport: PropertyChangeSupport
) {
fun getValue(): Int? = propValue
fun setValue( newValue: Int) {
val oldValue = propValue
propValue = newValue
changeSupport.firePropertyChange(propName, oldValue, newValue)
}
}
open class PropertyChangeAware {
val changeSupport = PropertyChangeSupport(this)
fun addPropertyChangeListener(listener: PropertyChangeListener) {
changeSupport.addPropertyChangeListener(listener)
}
fun removePropertyChangeListener(listener: PropertyChangeListener) {
changeSupport.removePropertyChangeListener(listener)
}
}
fun main(args: Array<String>) {
val p = Person("Bob", 89, isMarried = false)
val data = mapOf("lastname" to "Jones", "company" to "JetBrains")
for ((attrName, value) in data)
p.setAttribute(attrName, value)
println(p)
}
Here is the current output:
name = Bob
company = JetBrains
lastname = Jones
Person(name="Bob", age=89, isMarried=false) Bob Bob kotlin.Unit() -> kotlin.Unit
Thanks, again, for any help.
You should not use print() or println() functions inside toString() because they output their arguments to the standard output immediately instead of appending them to the string returned to the caller.
Let's examine the output kotlin.Unit() -> kotlin.Unit you're getting. It consists of two parts:
kotlin.Unit is the string representation of attributes!!.forEach { ... } expression. forEach function returns without value, and in Kotlin it's expressed by returning the Unit object value. Its string representation is appended to the string you're returning.
the second part, () -> kotlin.Unit, is also the string representation of the lambda function expression { for((attrName, value) in ...) }. This function takes no parameters, and returns without value, which means that its type is () -> Unit. Note that in Kotlin the block { ... } declares a local lambda function. If you instead want to run the code inside of that block, use the run function: run { ... }
The goal of toString function is to build the string representation of an object. And for that you can use buildString function:
override fun toString() = buildString {
append("Person(name=\"${name?:""}\", age=${age?:99999}, isMarried=$isMarried) ")
append("${_attributes?.get("name")} ").append("$name ")
this._attributes!!.forEach { (attrName, value) -> append("$attrName = $value") }
for ((attrName, value) in this._attributes!!) {
append("attribute $attrName = ${this._attributes!![attrName]}")
}
}
This function creates a StringBuilder and passes it as a receiver to its functional argument, where you call append or appendln on that receiver. Then buildString converts that string builder to a string and returns it.
I am new to kotlin. I wonder if this is possible
I wish to create a function that will change the value of the properties of the object and return the object itself. The main benefit is that I can chain this setter.
class Person {
var name:String? = null
var age:Int? = null
fun setter(propName:String, value:Any): Person{
return this.apply {
try {
// the line below caused error
this[propName] = value
} catch(e:Exception){
println(e.printStackTrace())
}
}
}
}
//usage
var person = Person(null,null)
person
.setter(name, "Baby")
.setter(age, 20)
But I get error "unknown references"
This question is marked as duplicate, however the possible duplicate question specifically want to change the property of "name", but I wish to change anyProperty that is pass from the function to object. Can't seem to connect the dot between two questions. #Moira Kindly provide answer that explain it. thankyou
Why not just simplify your answer to
fun setter(propName: String, value: Any): Person {
val property = this::class.memberProperties.find { it.name == propName }
when (property) {
is KMutableProperty<*> ->
property.setter.call(this, value)
null ->
// no such property
else ->
// immutable property
}
}
Java reflection isn't needed, its only effect is to stop non-trivial properties from being supported.
Also, if you call it operator fun set instead of fun setter, the
this[propName] = value
syntax can be used to call it.
After googling around, I think I can provide an answer, but relying on java instead of kotlin purely. It will be great if someone can provide a better answer in kotlin.
class Person(
var name: String,
val age: Int
){
fun setter(propName: String, value: Any): Person{
var isFieldExistAndNotFinal = false
try{
val field = this.javaClass.getDeclaredField(propName)
val isFieldFinal = (field.getModifiers() and java.lang.reflect.Modifier.FINAL == java.lang.reflect.Modifier.FINAL)
if(!isFieldFinal) {
// not final
isFieldExistAndNotFinal = true
}
// final variable cannot be changed
else throw ( Exception("field '$propName' is constant, in ${this.toString()}"))
} catch (e: Exception) {
// object does not have property
println("$e in ${this.toString()}")
}
if(isFieldExistAndNotFinal){
val property = this::class.memberProperties.find { it.name == propName }
if (property is KMutableProperty<*>) {
property.setter.call(this, value)
}
}
return this;
}
}
usage like this
person
.setter(propName = "age", value = 30.00)
.setter(propName = "asdf", value = "asdf")
.setter(propName = "name", value = "A Vidy")
You have error because when you do this[propName] = value you are trying to use this as a list, but it is not a list, it is a Person and it doesn't overload the [] operator.
What you can do is to add a check for the property that is setted:
class Person {
privavar name:String? = null
var age:Int? = null
fun setter(propName:String, value:Any): Person{
return this.apply {
if (propName == "name" && value is String?) {
it.name = value as String?
} else if (propName == "age" && value is Int?) {
it.age = value as Int?
} else {
// handle unknown property or value has incorrect type
}
}
}
}
Another more dynamic solution without reflection:
class Person {
private var fields: Map<String, Any?> = HashMap()
fun setter(propName:String, value:Any): Person{
return this.apply {
it.fields[propName] = value;
}
}
fun getName() = fields["name"]
}
If you want to get rid of the getters as well then you need to use reflection.
I'm wondering if it's possible in Kotlin to deserialize (restore property values) of a declared object, without having to manually assign the properties or resorting to reflection. The following snippet further explains:
object Foo: Serializable {
var propOne: String = ""
// ...
fun persist() {
serialize(this)
// no problem with serialization
}
fun restore(bytes: ByteArray) {
val fooObj: Foo = deserialize(bytes) as Foo
// It seems Kotlin allows us to use singleton as type!
// obvioulsly either of the following is wrong:
// this = fooObj
// Foo = fooObj
// ... is there a way to 'recover' the singleton (object) other than
// manual assignment of properties (or reflection) ???
}
}
There is no way to reassign the global reference to a singleton with a new instance. At most you can write out the properties during serialization, and then on deserialization directly read the properties and mutate the state in the original object. It will require custom code for you to assign the properties into the object either by direct assignment or reflection. It would be better if you make your own singleton mechanism that holds an instance that you can swap out to be another instance that you deserialize.
have faced with the same issue, and want to share with you my solution:
import com.fasterxml.jackson.databind.DeserializationFeature
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.databind.SerializationFeature
import java.io.File
import java.lang.reflect.Modifier
typealias ObjMap = HashMap<String, Any?>
fun <T : Any> T.getInstance() : Any? {
val target = if(this is Class<*>) this else javaClass
return target.getDeclaredField("INSTANCE")?.get(null)
}
class ObjectHelper {
companion object {
val mapper = ObjectMapper().apply {
enable(SerializationFeature.INDENT_OUTPUT)
configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
}
fun objectToMap(obj: Any): ObjMap {
var res = ObjMap()
val instance = obj.getInstance()
val o = instance ?: obj
o.javaClass.declaredFields.forEach {
if(it.name != "INSTANCE") {
it.isAccessible = true
val value = if(Modifier.isStatic(it.modifiers)) it.get(null) else it.get(o)
res[it.name] = value
}
}
o.javaClass.classes.forEach {
res[it.simpleName] = objectToMap(it)
}
return res
}
fun saveObject(path: String, obj: Any) {
mapper.writeValue(File(path), objectToMap(obj))
}
fun loadObject(path: String, obj: Any) {
val json = mapper.readValue<HashMap<*,*>>(File(path), HashMap::class.java) as ObjMap
loadObject(obj, json)
}
fun loadObject(obj: Any, props: ObjMap) {
val objectParam = mapper.writeValueAsString(props)
mapper.readValue(objectParam, obj::class.java)
obj.javaClass.classes.forEach {
val instance = it.getInstance()
val map = props[it.simpleName]
if(map != null && instance != null) {
loadObject(instance, map as ObjMap)
}
}
}
}
}
Usage example:
object TestObj {
var f1: String = "f1"
var f2: String = "f2"
object TestObj_2 {
var f1: String = "f1_1"
var f2: String = "f2_2"
}
}
TestObj.f1 = "aaa"
saveObject("out.json", TestObj)
TestObj.f1 = "bbb"
loadObject("out.json", TestObj)
println(TestObj.f1)
Result will be "aaa".