Context
Using a declarative approach in Kotlin, need to copy a single name property from List of User objects to a List of UserDetail objects based on matching id properties as shown below:
val users = Arrays.asList(
User(1, "a"),
User(2, "b")
)
val details = Arrays.asList(
UserDetail(1),
UserDetail(2)
)
val detailsWithName = copyNameToUser(users, details)
Models are:
class User {
var id = -1;
var name = "" // given for all Users
constructor(id: Int, name: String)
// ...
}
class UserDetail {
var id = -1;
var name = "" // blank for all UserDetails
constructor(id: Int)
// ...
}
Problem
Tried to use a declarative approach via forEach iterable function:
fun copyNameToDetails(users: List<User>, details: List<UserDetail>): List<UserDetail> {
details.forEach(d ->
users.forEach(u ->
if (d.id == u.id) {
d.name = u.name
}
)
)
return details
}
This can be achieved in Java as shown below:
private static List<UserDetail> copyNameToDetails(List<User> users, List<UserDetail> details) {
for (UserDetail d: details) {
for (User u : users) {
if (d.id == u.id) {
d.name = u.name;
}
}
}
return details;
}
Question
How can this be done in Kotlin using a declarative approach?
You make too many iterations over both lists (users.size * details.size) so creating a hashmap can fix it a bit:
fun copyNameToUsers(users: List<User>, details: List<UserDetail>): List<UserDetail> {
val usersById = users.associate { it.id to it }
details.forEach { d ->
usersById[d.id]?.let { d.name = it.name }
}
return details
}
An other approach with non mutable values :
data class User(val id: Int = -1, val name: String = "")
data class UserDetail(val id: Int = -1, val name: String = "")
private fun List<UserDetail>.copyNameToUser(users: List<User>): List<UserDetail> = map { userDetail ->
users.firstOrNull { userDetail.id == it.id }?.let { userDetail.copy(name = it.name) } ?: userDetail
}
Related
I want to implement search functionality among lists of banks in my app.
So somehow I need to use stringResId() but you can't call it without composable func(). Also by using Resources.getSystem().getString() is giving me resources not found exception.
This is my viewModel code
class BankViewModel: ViewModel() {
private val _bankAccount = MutableStateFlow(BankAccount())
val bankAccount: StateFlow<BankAccount> = _bankAccount.asStateFlow()
var bankList = mutableStateOf(Banks)
private var cachedBankList = listOf<Bank>()
private var isSearchStarting = true
var isSearching = mutableStateOf(false)
fun updateBankSearch(searchName: String) {
_bankAccount.update { bankAccount ->
bankAccount.copy(bankName = searchName)
}
}
fun searchBankName(query: String) {
val listToSearch = if(isSearchStarting) {
bankList.value
}else {
cachedBankList
}
viewModelScope.launch {
if (query.isEmpty()) {
bankList.value = cachedBankList
isSearching.value = false
isSearchStarting = true
return#launch
}
val results = listToSearch.filter {
Resources.getSystem().getString(it.bankName).contains(query.trim(), ignoreCase = true)
}
if (isSearchStarting) {
cachedBankList = bankList.value
isSearchStarting = false
}
bankList.value = results
isSearching.value = true
}
}
}
This is my Bank
data class Bank (
#StringRes val bankName: Int,
#DrawableRes val bankLogo: Int = R.drawable.bank_image_2
)
So my question is how can I get a string by using id so that I can compare it with the query??
You need to use the Application Context to retrieve resources like these.
If you're not using any DI framework, or you don't want to use custom ViewModelProvider.Factory, extend AndroidViewModel (which holds a reference to Application) instead of regular ViewModel.
Ideally ViewModels shouldn't contain any Android-specific objects, and you would use some custom StringProvider, or something similar, but that's not a topic of your question.
I'm trying to do a quite simple task: assign properties to an object and return that same object after retrieving the infos with a REST call.
In my runBlocking block I use the apply function to change the properties of my object, but after trying different ways to assign them, instantiate the object itself, modifying constructing logic of the object, I still get an object with the default values.
Here's my Info object:
class DrivingLicenceInfo {
var type : String = ""
var nationality : String = ""
var number : String = ""
var releaseDate : String = ""
var expiryDate : String = ""
}
Here's the method which gives me problems:
private fun getDerivingLicenceInfoAndWaitForCompletion(): DrivingLicenceInfo {
return runBlocking {
val response = retrieveDrivingLicenceInfoAsync().await()
if (response.isSuccessful) {
var info = DrivingLicenceInfo()
response.body()?.let {
info.apply {
it.data.let { data ->
val type = data.guy
val drivingLicenseNationality = data.drivingLicenseNationality
val drivingLicenseNumber = data.drivingLicenseNumber
val drivingReleaseDate = data.drivingReleaseDate
val drivingExpiryDate = data.drivingExpiryDate
this.type = type
this.nationality = drivingLicenseNationality
this.number = drivingLicenseNumber
this.releaseDate = drivingReleaseDate
this.expiryDate = drivingExpiryDate
}
}
info
Log.i("driving.info.call", info.type)
}
}
DrivingLicenceInfo()
}
}
And here's where I use it, in my Main, and where I get an info object with empty strings as properties
private void getDrivingLicenceData() {
DrivingLicenceInfoService service = new DrivingLicenceInfoServiceImpl(context);
DrivingLicenceInfo info = service.getDrivingLicenceInfo();
Log.i("driving.info.main",info.getType());
profileViewModel.licenceNumber.postValue(info.getNumber());
profileViewModel.licenceExpiryDate.postValue(info.getExpiryDate());
}
The log in the runBlocking correctly shows the property, the log in my Main doesn't even show up.
Using the debugger I am able to see that info has empty strings as value.
Could somebody help me to figure out what I'm doing wrong?
Thank you
Beside #JeelVankhede giving you the main reason for your problem, I suggest some minor code improvements as well. I personally feel this is ways less verbose and better readable
private fun getDrivingLicenceInfoAndWaitForCompletion(): DrivingLicenceInfo {
return runBlocking {
val response = retrieveDrivingLicenceInfoAsync().await()
var info = DrivingLicenceInfo()
return if (response.isSuccessful) {
response.body()?.let {
info.apply {
type = it.data.guy
nationality = it.data.drivingLicenseNationality
number = it.data.drivingLicenseNumber
releaseDate = it.data.drivingReleaseDate
expiryDate = it.data.drivingExpiryDate
}
Log.i("driving.info.call", info.type)
info
} ?: info
} else { info }
}
}
Since #JeelVankhede already told you the main reason of your problem and I also have some suggestions apart from the one given by #WarrenFaith.
If DrivingLicenceInfo is a model class you can declare it as data class like
data class DrivingLicenceInfo (
val type : String = "",
val nationality : String = "",
val number : String = "",
val releaseDate : String = "",
val expiryDate : String = ""
)
you can read more about data class here.
And then you can write your function as
private fun getDerivingLicenceInfoAndWaitForCompletion(): DrivingLicenceInfo {
val info = runBlocking {
val response = retrieveDrivingLicenceInfoAsync().await()
if (response.isSuccessful) {
response.body()?.let {
it.data.let { data ->
DrivingLicenceInfo(
type = data.guy,
nationality = data.drivingLicenseNationality,
number = data.drivingLicenseNumber,
releaseDate = data.drivingReleaseDate,
expiryDate = data.drivingExpiryDate
)
}
} ?: DrivingLicenceInfo()
} else {
DrivingLicenceInfo()
}
}
Log.i("driving.info.call", info.type)
return info
}
I have trouble with the management with one-to-many relations between Kotlin objects using Realm. I don't understand how to do some insert or update.
Here my two objects with one-to-many relation between exam and career.
open class Career : RealmObject() {
#PrimaryKey
var id: Long = 1
var status: String = CareerStatus.ACTIVE.value
var careerName: String? = null
var exams: RealmList<Exam>? = null
}
open class Exam : RealmObject() {
#PrimaryKey
var id: Long = 1
var teachers: String? = null
var lode: Boolean? = null
var score: String = ""
var exam: String = ""
var examDescription: String? = null
var date: Date = Date()
var cfu: Long = Long.MIN_VALUE
#LinkingObjects("exams")
val career: RealmResults<Career>? = null
}
Here the two class Manager the manage the read/write on Realm
class CareerManager : DatabaseManager() {
fun findActiveCareer(): Career? {
return realm.where(Career::class.java).equalTo("status", CareerStatus.ACTIVE.value).findFirst()
}
fun insertExamInCareer(exam: Exam) {
realm.executeTransaction {
var activeCareer: Career = findActiveCareer()
?: throw Resources.NotFoundException("No active career found")
activeCareer.exams?.add(exam)
realm.copyToRealmOrUpdate(exam)
}
}
fun closeActiveCareer() {
realm.executeTransaction {
val activeCareer: Career = findActiveCareer()
?: throw Resources.NotFoundException("No active career found")
activeCareer.status = CareerStatus.TERMINATED.value
}
}
}
class ExamManager : DatabaseManager() {
fun findAll(): List<Exam> {
val findAll = realm.where(Exam::class.java).findAll()
return realm.copyFromRealm(findAll).toList()
}
fun findAllActive(): List<Exam> {
val findAll = realm.where(Exam::class.java).equalTo("career.status", CareerStatus.ACTIVE.value).findAll()
return realm.copyFromRealm(findAll).toList()
}
fun insert(exam: Exam): Long {
realm.beginTransaction()
var newId: Long = 1
if (realm.where(Exam::class.java).max("id") != null) {
newId = realm.where(Exam::class.java).max("id") as Long + 2
}
val examToSave = realm.createObject(Exam::class.java, newId)
examToSave.exam = exam.exam
examToSave.examDescription = exam.examDescription
examToSave.date = exam.date
examToSave.teachers = exam.teachers
examToSave.score = exam.score
examToSave.lode = exam.lode
examToSave.cfu = exam.cfu
realm.commitTransaction()
CareerManager().updateCareerExam(findAll())
return newId
}
}
In my application I need to insert some exams in my career that is actually in ACTIVE state. For the insert I use CareerManager().insertExamInCareer(exam) this call (before I try to use ExamManager().insert(exam) but doesn't work).
Another use case is when I need to close a career and add the exam to another career. I do this in this manner
CareerManager().closeActiveCareer()
CareerManager().createCareer()
CareerManager().insertExamInCareer(exam)
The exam in the two career are the same, but they had to be different and in Exam there must have been two records, not one
Good day, i'm stuck figuring out how to get a single object from a list, i did google but all the topics show how to return a List with sorted objects or something similar.
I have a User Class
class User() {
var email: String = ""
var firstname: String = ""
var lastname: String = ""
var password: String = ""
var image: String = ""
var userId: String = ""
constructor(email:String,
firstname: String,
lastname: String,
password: String,
image: String, userId : String) : this() {
this.email = email
this.firstname = firstname
this.lastname = lastname
this.password = password
this.image = image
this.userId = userId
}
}
In java i would write something like
User getUserById(String id) {
User user = null;
for(int i = 0; i < myList.size;i++;) {
if(id == myList.get(i).getUserId())
user = myList.get(i)
}
return user;
}
How can i achieve the same result in kotlin?
You can do this with find, which gives you the first element of a list that matches a given predicate (or null, if none matched):
val user: User? = myList.find { it.userId == id }
Or if you really do need the last element that matches the predicate, as your Java example code does, you can use last:
val user: User? = myList.last { it.userId == id }
Simplify
val user: User = myList.single { it.userId == id }
or if may list not have your filter
val user: User? = myList.singleOrNull{ it.userId == id }
If you don't want to deal with null objects, try this:
val index = myList.indexOfFirst { it.userId == id } // -1 if not found
if (index >= 0) {
val user = myList[index]
// do something with user
}
You can use this extension function also which return pair Pair(Boolean,T)
e.g
val id=2
val item= myList.customContains{it-> it.userId ==id}
if(item.first){
item.second //your object
// your code here
}else{
// if item no present
}
fun <E> List<E>.customContains(function: (currentItem: E) -> Boolean): Pair<Boolean, E?> {
for (current in 0 until this.size) {
if (function(this[current])) {
return Pair(true, this[current])
}
}
return Pair(false, null)
}
I have the following methods on my code:
fun saveArticles(data: JSONArray) {
var active = String()
for (i in 0..data.length().minus(1)) // create string
val articles = Select.from(Article::class.java).list()
val iterator = articles.iterator()
while (iterator.hasNext()) {
val article = iterator.next() as Article
if (!active.contains(Regex(article.id.toString()))) article.delete()
}
}
fun saveDossiers(data: JSONArray) {
var active = String()
for (i in 0..data.length().minus(1)) // create string
val dossiers = Select.from(Dossier::class.java).list()
val iterator = dossiers.iterator()
while (iterator.hasNext()) {
val dossier = iterator.next() as Dossier
if (!active.contains(Regex(dossier.id.toString()))) dossier.delete()
}
}
fun saveVideos(data: JSONArray) {
var active = String()
for (i in 0..data.length().minus(1)) // create string
val videos = Select.from(Video::class.java).list()
val iterator = videos.iterator()
while (iterator.hasNext()) {
val video = iterator.next() as Video
if (!active.contains(Regex(video.id.toString()))) video.delete()
}
}
As you can see, all the methods do exactly the same thing. The only difference is the Class type of the object I'm working at the moment. Can I somehow create a single method with a parameter of Class type, and depending of the type change the class I need to work? Something like this:
fun saveVideos(data: JSONArray, type: Class) {
var active = String()
for (i in 0..data.length().minus(1)) // create string
val list = Select.from(type).list()
val iterator = list.iterator()
while (iterator.hasNext()) {
val item = iterator.next() as type
if (!active.contains(Regex((item as type).id.toString()))) item.delete()
}
}
You need to extract an interface and use a reified generic.
interface Blabla {
fun delete()
val id: Int
}
inline fun <reified T : Blabla>saveVideos(data: JSONArray) {
var active = String()
for (i in 0..data.length().minus(1)) // create string
val list = Select.from(T::class.java).list()
val iterator = list.iterator()
while (iterator.hasNext()) {
val item = iterator.next() as T
if (Regex(item.id.toString()) !in active) item.delete()
}
}
This should work.
Also, I highly recommend you to use the Kotlin collection library, like this.
inline fun <reified T : Blabla>saveVideos(data: JSONArray) {
val active = ""
for (i in 0 until data.length()) {} // create string
val list = Select.from(T::class.java).list()
list
.map { it as T }
.filter { Regex(it.id.toString()) !in active }
.forEach { it.delete() }
}
And you can even replace forEach { it.delete() } with forEach(T::delete)