So I am trying to save a list of string pairs into my database but having some issues with the TypeConverter, I tried following guides ans other SO posts but can't figure out whats wrong...
My Entity:
#Entity
data class Credential(
#PrimaryKey()
val id: String,
#ColumnInfo(name = "name")
val name: String,
#ColumnInfo(name = "url")
val url: String?,
#TypeConverters(ListPairTypeConverter::class)
#ColumnInfo(name = "fields")
val fields: List<Pair<String, String>>
)
My Type Converter:
class ListPairTypeConverter {
#TypeConverter
fun storedStringToPairList(value: String): List<Pair<String, String>> {
return value.split("~!!!!!~").map {
val vals = it.split("!~~~~~!")
Pair(vals[0], vals[1])
}
}
#TypeConverter
fun pairListToStoredString(pl: List<Pair<String, String>>): String {
return pl.joinToString(separator = "~!!!!!~") { it.first + "!~~~~~!" + it.second }
}
}
My Error:
error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.
private final java.util.List<kotlin.Pair<java.lang.String, java.lang.String>> fields = null;
^
You are adding type converter at wrong place. instead of
#TypeConverters(ListPairTypeConverter::class)
#ColumnInfo(name = "fields")
val fields: List<Pair<String, String>>
You need to add at here
#Database(entities = [User::class], version = 1)
#TypeConverters(ListPairTypeConverter::class)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDao(): UserDao
}
So I have a sample app that is currently using Retrofit to fetch data and display it in a recyclerview with its custom adapter. I want to pass the data to the a more details page when I click on a character name on my recyclerView. I found some tutorials and decided to use the Parcelize annotation like this:
#Parcelize data class Character (
val charID: Long,
val name: String,
val birthday: String,
val occupation: List<String>,
val img: String,
val status: String,
val nickname: String,
val appearance: List<Long>,
val portrayed: String,
val category: String,
val betterCallSaulAppearance: List<Long> ) : Parcelable
My adapter looks like this:
override fun onBindViewHolder(holder: ViewHolder, position: Int) {
val character = characters[position]
holder.characterNameText.text = character.name
holder.characterNameText.setOnClickListener {
holder.passData(character)
}
}
override fun getItemCount() = characters.size
class ViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView) {
val characterNameText = itemView.findViewById<TextView>(R.id.character_name)
fun passData(character : Character) {
val intent = Intent(itemView.context, CharacterDetails::class.java)
intent.putExtra(CHARACTER, character)
itemView.context.startActivity(intent)
}
}
And in the CharacterDetails Activity it looks like this:
companion object {
const val CHARACTER = "character"
}
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_character_details)
val bundle = intent.extras
val character = bundle!!.getParcelable<Character>(CHARACTER)
val characterName = findViewById<TextView>(R.id.character_details_name)
Yet I get a
java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
at com.example.myapplication.models.Character.writeToParcel(Unknown Source:85)
I'm still new to this so I really need your help.Thanks!
Obviously, the error caused by the list reference of the data class is null. You can modify the code like this.
#Parcelize data class Character (
val charID: Long,
val name: String,
val birthday: String,
val occupation: List<String>?,
val img: String,
val status: String,
val nickname: String,
val appearance: List<Long>?,
val portrayed: String,
val category: String,
val betterCallSaulAppearance: List<Long>? ) : Parcelable
I have a mutableLIst:
var books = mutableListOf<Book>()
model "Book" is:
data class Book(val title: String, val id: Int)
My code is:
button2.setOnClickListener{
val delFragment = DelFragment()
val booksforDel = Bundle()
booksforDel.putStringArrayList("books", books as ArrayList<String>)
delFragment.setArguments(booksforDel)
val manager = supportFragmentManager
delFragment.show(manager,"Delete Book")
}
in Fragment I try to get data:
val booksForDelete = getArguments()?.getStringArrayList("books")!!
And get Error:
java.lang.ArrayStoreException: source[0] of type com.example.http_example.model.Book cannot be stored in destination array of type java.lang.String[]
How send a data from mutableList "books" to Bundle in DialogFragment?
You can implement Parcelable interface:
data class Book(val title: String, val id: Int) : Parcelable {
constructor(source: Parcel) : this(
source.readString()!!,
source.readInt()
)
override fun describeContents() = 0
override fun writeToParcel(dest: Parcel, flags: Int) = with(dest) {
writeString(title)
writeInt(id)
}
companion object {
#JvmField
val CREATOR: Parcelable.Creator<Book> = object : Parcelable.Creator<Book> {
override fun createFromParcel(source: Parcel): Book = Book(source)
override fun newArray(size: Int): Array<Book?> = arrayOfNulls(size)
}
}
}
And use it like the following:
var books = mutableListOf<Book>()
val booksforDel = Bundle()
booksforDel.putParcelableArray("books", books.toTypedArray())
Ann to retrieve books in a Fragment:
val booksForDelete = arguments?.getParcelableArray("books")
I want to add a delegated property to my Composition class, as follows
#Entity
data class Composition(
val author: String="",
val background: String?,
val description: String="",
val downloadURL: String="",
val duration: String="",
val headPortrait: String?,
#PrimaryKey val id: String,
val isLike: Boolean,
val likeAmount: String="",
val playingAmount: Int=0,
val replyAmount: String?,
val showStyle: String?,
val title: String?,
val userId: String?,
val commentAmount: String?,
val cover: String=""
){
val showDuration by lazy{
val minutes = duration.toInt() /60
val seconds =duration.toInt()%60
"$minutes:$seconds"
}
}
But there gona be a compile error because delegated property can not be saved in database. So i want to
add an
Ignore annotation to this field. What a pity that Androidstuio will throws a complain "This annotation is not applicable to target 'member property with delegate" . Who has ideas for this problem?
As user IR42 points out in his comment, you can use #delegate:Ignore.
I am using Kotlin 1.30. I have the following entity classes that will be populated from the API. And some of the properties could be null from the API so I have declared them using the safe null type.
However, I will map this entity class to my domain model class. And just wondering what is the best way to handle the null types?
I have 2 ideas on how to do this when I map the classes.
declare all the equivalent properties as safe null types
use the elivs operator to return either a empty string or a emptylist
In the following snippet I am using the elvis operator. Just wondering what is the best practice for this?
class LoginResponseDomainMapperImp : LoginResponseDomainMapper {
override fun map(entity: LoginResponseEntity): LoginResponse {
return LoginResponse(
entity.token ?: "",
mapUsers(entity.user),
mapEnterprises(entity.enterprises ?: emptyList()),
mapVendors(entity.vendors ?: emptyList()))
}
private fun mapUsers(userEntity: UserEntity?): User {
return User(
userEntity?.id,
userEntity?.email,
userEntity?.firstName,
userEntity?.lastName,
userEntity?.phone,
userEntity?.address,
userEntity?.dob,
userEntity?.customer,
userEntity?.enterpriseIds ?: emptyList(),
userEntity?.vendorIds ?: emptyList())
}
private fun mapEnterprises(enterprisesEntity: List<EnterprisesEntity>): List<Enterprises> {
val enterpriseList = mutableListOf<Enterprises>()
enterprisesEntity.forEach {
val enterprise = Enterprises(
it.id,
it.enterpriseName,
it.typeLabel,
it.country,
it.imageId,
it.managers,
it.members,
it.stripe,
it.locations)
enterpriseList.add(enterprise)
}
return enterpriseList.toList()
}
private fun mapVendors(vendorsEntity: List<VendorsEntity>): List<Vendors> {
val vendorList = mutableListOf<Vendors>()
vendorsEntity.forEach {
val vendor = Vendors(
it.id,
it.vendorName,
it.typeLabel,
it.userRole,
it.latitude,
it.longitude,
it.partner,
it.country,
it.imageId,
it.stripe)
vendorList.add(vendor)
}
return vendorList.toList()
}
}
Entity class that will populate from the API, so any of these could be null
data class LoginResponseEntity(
#SerializedName("token") val token: String?,
#SerializedName("user") val user: UserEntity?,
#SerializedName("enterprises") val enterprises: List<EnterprisesEntity>?,
#SerializedName("vendors") val vendors: List<VendorsEntity>?)
data class UserEntity(
#SerializedName("id") val id: String?,
#SerializedName("email") val email: String?,
#SerializedName("first_name") val firstName: String?,
#SerializedName("last_name") val lastName: String?,
#SerializedName("phone") val phone: String?,
#SerializedName("address") val address: String?,
#SerializedName("dob") val dob: String?,
#SerializedName("customer") val customer: String?,
#SerializedName("enterprise_ids") val enterpriseIds: List<String>?,
#SerializedName("vendor_ids") val vendorIds: List<String>?)
data class EnterprisesEntity(
#SerializedName("id") val id: String?,
#SerializedName("enterprise_name") val enterpriseName: String?,
#SerializedName("type_label") val typeLabel: String?,
#SerializedName("referral_code") val referralCode: String?,
#SerializedName("country") val country: String?,
#SerializedName("image_id") val imageId: String?,
#SerializedName("managers") val managers: List<String>?,
#SerializedName("members") val members: List<String>?,
#SerializedName("stripe") val stripe: Boolean,
#SerializedName("locations") val locations: List<String>?)
data class VendorsEntity(
#SerializedName("id") val id: String?,
#SerializedName("vendor_name") val vendorName: String?,
#SerializedName("type_label") val typeLabel: String?,
#SerializedName("user_role") val userRole: String?,
#SerializedName("latitude") val latitude: Float,
#SerializedName("longitude") val longitude: Float,
#SerializedName("partner") val partner: Boolean,
#SerializedName("country") val country: String?,
#SerializedName("image_id") val imageId: String?,
#SerializedName("stripe") val stripe: Boolean)
Data model class in the domain, Its it better to declare them all safe null types?
data class LoginResponse(
val token: String,
val user: User?,
val enterprises: List<Enterprises>,
val vendors: List<Vendors>)
data class User(
val id: String?,
val email: String?,
val firstName: String?,
val lastName: String?,
val phone: String?,
val address: String?,
val dob: String?,
val customer: String?,
val enterpriseIds: List<String>,
val vendorIds: List<String>)
data class Enterprises(
val id: String,
val enterpriseName: String,
val typeLabel: String,
val country: String,
val imageId: String,
val managers: List<String>,
val members: List<String>,
val stripe: Boolean,
val locations: List<String>)
data class Vendors(
val id: String,
val vendorName: String,
val typeLabel: String?,
val userRole: String,
val latitude: Float,
val longitude: Float,
val partner: Boolean,
val country: String?,
val imageId: String,
val stripe: Boolean)
First of all there are no safe null types in Kotlin. A variable is either nullable or not.
If the API delivers null values, either by absence or by setting them explicitely null, your data classes should reflect that in the way that those variables are nullable (question mark ? right after the data type).
The moment you map those data classes to your entities (domain model) you should handle the null case properly. Since it is a valid case, that the API serves null values, which you expect, you should handle that case by assigning a default value.
Using the elvis operator is just a way to deal with nullable types elegantely, but if you use it, remains your choice.
If you declare all the properties as nullable that's not much better than Java, even when you access them with the null safety operator. If your JSON properties have null value, that means that in your business logic they don't always have a value, and is your responsibility to handle that, by fallback to a default value (i.e. emptyList() or ""), or maybe something more complicated like redirecting to a sign in screen.