I am new to coding, so was using the google developer tutorial to create an app. I was doing this letter by letter so I am not sure why I have an unresolved reference for PlaceResponse. I have created a data class, which I have changed from var and val but unfortunately I must have missed something because the code below is still having issues placeresponse is being labelled as an unresolved reference
fun read(): List<Place> {
var itemType = object : TypeToken<List<PlacesResponse>>() {}.type
var reader = InputStreamReader(inputStream)
return gson.fromJson<List<PlaceResponse>>(reader, itemType).map {
it.toPlace()
}
}
}
private val places: List<Place> by lazy{
PlacesReader(this).read()
}
data class Place(
val name:String,
val LatLng:LatLng,
val address: String,
val rating: Float
Related
I'm learning myself some android programming (beginning level) and following a tutorial. I'm getting an error when I run/build the project. Expecting member declaration. I've checked the code for typos and syntax errors. I've googled this, but I'm just not sure what it means or what to look for to fix it.
Are other classes used in the project automatically seen by the MainActivity class?
Code in part:
MainActivity.kt:
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
class MainActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
}
val friendlyDestroyer = Destroyer("Invincible")
val friendlyCarrier = Carrier("Indomitable")
val enemyDestroyer = Destroyer("Grey Death")
val enemyCarrier = Carrier("Big Grey Death")
val friendlyShipyard = ShipYard()
friendlyDestroyer.takeDamage(enemyDestroyer.shootShell())
friendlyDestroyer.takeDamage(enemyCarrier.launchAerialAttack())
// Fight back
enemyCarrier.takeDamage(friendlyCarrier.launchAerialAttack())
enemyCarrier.takeDamage(friendlyDestroyer.shootShell())
...
Any line that has an instance to a class with a function call shows the red squiggly line and the error.
In the line: friendlyDestroyer.takeDamage(enemyDestroyer.shootShell()), it shows the expecting member declaration error at just about every part of the line.
This happens on every instance of a class making a call to a class.
I'm not seeing any errors for the other classes/files.
Destroyer.kt:
package com.johndcowan.basicclasses
class Destroyer(name: String) {
// what is the name of the ship
var name: String = ""
private set
// what type of ship is it
// alwys a destroyer
val type = "Destroyer"
// how much the ship can take before sinking
private var hullIntegrity = 200
// how many shots left in the arsenal
var ammo = 1
// cannot be directly set externally
private set
// no external access whatsoever
private var shotPower = 60
// has the ship been sunk
private var sunk = false
// this code runs as the instance is being initialized
init {
// so we can use the name parameter
this.name = "$type $name"
}
fun takeDamage(damageTaken: Int) {
if (!sunk) {
hullIntegrity -= damageTaken
println("$name hull integrity = $hullIntegrity")
if (hullIntegrity <= 0){
println("Destroyer $name has been sunk")
sunk = true
}
} else {
// Already sunk
println("Error Ship does not exist")
}
}
fun shootShell():Int {
// let the calling code know how much damage to do
return if (ammo > 0) {
ammo--
shotPower
}else{
0
}
}
...
What am I missing or not seeing?
Thanks for any tips.
Snapshot of my firebase realtime database
I want to extract the entire data under the "Orders" node, please tell me how should I model my data class for android in Kotlin?
I tried with this type of modeling,
After getting the reference of (Orders/uid/)
Order.kt
data class Order(
val items:ArrayList<Myitems>=ArrayList(),
val timeStamp:Long=0,
val totalCost:Int=0
)
MyItems.kt
data class MyItems(
val Item:ArrayList<Menu>=ArrayList()
)
Menu.kt
data class Menu(
val menCategory:String="",
val menName:String="",
val menImage:String="",
val menId:String="",
val menQuantity:Int=0,
val menCost:Int=0
)
After a lot of thinking and research online. I was finally able to model my classes and call add value event listener to it. Here it goes:
Order.kt
data class Order(
val items: ArrayList<HashMap<String, Any>> = ArrayList(),
val timeStamp: Long = 0,
val totalCost: Int = 0
)
OItem.kt
data class OItem(
val menCategory: String = "",
val menId: String = "",
val menImage: String = "",
val menName: String = "",
val menPrice: Int = 0,
var menQuantity: Int = 0
)
MainActivity.kt
val uid = FirebaseAuth.getInstance().uid
val ref = FirebaseDatabase.getInstance().getReference("Orders/$uid")
ref.addListenerForSingleValueEvent(object : ValueEventListener {
override fun onCancelled(error: DatabaseError) {
//
}
override fun onDataChange(p0: DataSnapshot) {
p0.children.forEach {
val order = it.getValue(Order::class.java)
ordList.add(order!!)
}
Log.d("hf", ordList.toString())
}
})
I migrated from paging 2 to paging 3. I tried to implement ItemKeyedDataSource of Paging 2 to Paging library 3. But the problem I was facing is, the same value(currentJodId) was passed as the nextkey in two sequential Pages loaded. And After that app crashes. but if I add "keyReuseSupported = true" in DataSource, app does not crash. But it started calling same item id as the nextkey.
JobSliderRestApi.kt
#GET("job/list/slides")
fun getDetailOfSelectedJob(
#Query("current_job") currentJodId: Int?,
#Query("limit") jobLimit: Int?,
#Query("search_in") fetchType: String?
): Single<Response<JobViewResponse>>
JobViewResponse.kt
data class JobViewResponse(
#SerializedName("data") val data: ArrayList<JobDetail>?
) : BaseResponse()
JobDetail.kt
data class JobDetail(
#SerializedName("job_id") val jobId: Int,
#SerializedName("tuition_type") val jobType: String?,
#SerializedName("class_image") val jobImage: String,
#SerializedName("salary") val salary: String,
#SerializedName("no_of_student") val noOfStudent: Int,
#SerializedName("student_gender") val studentGender: String,
#SerializedName("tutor_gender") val preferredTutor: String,
#SerializedName("days_per_week") val daysPerWeek: String?,
#SerializedName("other_req") val otherReq: String?,
#SerializedName("latitude") val latitude: Double?,
#SerializedName("longitude") val longitude: Double?,
#SerializedName("area") val area: String,
#SerializedName("tutoring_time") val tutoringTime: String?,
#SerializedName("posted_date") val postedDate: String?,
#SerializedName("subjects") val subjects: String,
#SerializedName("title") val title: String
)
JodSliderDataSource.kt
class JodSliderDataSource #Inject constructor(
private val jobSliderRestApi: JobSliderRestApi
): RxPagingSource<Int, JobDetail>() {
// override val keyReuseSupported = true
#ExperimentalPagingApi
override fun getRefreshKey(state: PagingState<Int, JobDetail>): Int? {
return state.anchorPosition?.let {
state.closestItemToPosition(it)?.jobId
}
}
override fun loadSingle(params: LoadParams<Int>): Single<LoadResult<Int, JobDetail>> {
return jobSliderRestApi.getDetailOfSelectedJob(42673, 2, "next").toSingle()
.subscribeOn(Schedulers.io())
.map { jobResponse -> toLoadResult(jobResponse.data) }
.onErrorReturn { LoadResult.Error(it) }
}
private fun toLoadResult(data: ArrayList<JobDetail>): LoadResult<Int, JobDetail> {
return LoadResult.Page(data = data, prevKey = null, nextKey = data.lastOrNull()?.jobId)
}
}
I was getting the same error and this is what worked for me. In the JodSliderDataSource class, toLoadResult method, set the nextKey parameter value by getting the page number from the response data and adding one.
private fun toLoadResult(
data: ArrayList<JobDetail>
): LoadResult<Int, JobDetail> {
return LoadResult.Page(
data = data,
prevKey = null,
nextKey = data.lastOrNull()?.jobId + 1 // Add one to the page number here.
)
}
I have read the artical. https://proandroiddev.com/android-camerax-tap-to-focus-pinch-to-zoom-zoom-slider-eb88f3aa6fc6
I add Code A to the office camerx sample. https://github.com/android/camera-samples/tree/master/CameraXBasic
The sample code use camerax "1.0.0-alpha06"
I get the error Unresolved reference for zoomRatio, you can see Image 1, how can I fix it?
Code A
private fun setUpPinchToZoom() {
val cameraControl = CameraX.getCameraControl(lensFacing)
val cameraInfo = CameraX.getCameraInfo(lensFacing)
val listener = object : ScaleGestureDetector.SimpleOnScaleGestureListener() {
override fun onScale(detector: ScaleGestureDetector): Boolean {
val currentZoomRatio: Float = cameraInfo.zoomRatio.value ?: 0F
val delta = detector.scaleFactor
cameraControl.setZoomRatio(currentZoomRatio * delta)
return true
}
}
val scaleGestureDetector = ScaleGestureDetector(context, listener)
viewFinder.setOnTouchListener { _, event ->
scaleGestureDetector.onTouchEvent(event)
return#setOnTouchListener true
}
}
Image 1
Zoom controls have been added on version 1.0.0-alpha07. You need to update your code to use at least camera-Core version 1.0.0-alpha07: https://developer.android.com/jetpack/androidx/releases/camera
I have Parent-Search-Child system as below:
class Room
class Building {
fun find(by: By) = Room()
}
sealed class By {
abstract fun search(): Room
class ById(id: String) : By() {
override fun search(): Room = Room() // epic search method
}
class ByName(name: String) : By() {
override fun search(): Room = Room() // epic search method
}
class Byurpose(purpose: String) : By() {
override fun search(): Room = Room() // epic search method
}
companion object {
fun id(id: String) = ById(id)
fun name(name: String) = ByName(name)
fun purpose(purpose: String) = Byurpose(purpose)
}
}
Which can be used as follows:
val building = Building()
val room = building.find(By.name("Toilet"))
However, I am not very satisfied with the current syntax, which could be much less verbose in Kotlin. In addition, building.find can appear thousands times in the code. I could implement it differently, but actually I don't own Room, Building or By classes, so I can't. Thus this was my approach:
I implemented context class that stores Building reference, and use it internally as source for search methods:
class BuildingContext(private val building: Building) {
fun String.findById() = building.find(By.id(this))
fun String.findByName() = building.find(By.name(this))
fun String.findByPurpose() = building.find(By.purpose(this))
}
It can be used as below:
with(BuildingContext(building)) {
val room2 = "Toilet".findByName()
}
After that I noticed that I only use one search method in 99% cases, so (for sake of even shorter syntax!) I implemented following classes:
object AlwaysSearchById {
fun String.find(building: Building) = building.find(By.id(this))
}
object AlwaysSearchByName {
fun String.find(building: Building) = building.find(By.name(this))
}
object AlwaysSearchByPurpose {
fun String.find(building: Building) = building.find(By.purpose(this))
}
Which can be used this way:
with(AlwaysSearchByName) {
val room3 = "Toilet".find(building)
}
Unfortunately, building reference appears again. The ideal syntax would be "Toilet".find(). I could fix it re-implementing Always~ classes as follows:
class AlwaysSearchByNameV2(private val building: Building) {
fun String.find() = building.find(By.name(this))
}
And it would be used as below:
with(AlwaysSearchByNameV2(building)) {
val room = "Toilet".find()
}
But it some cases, I would like to access BuildingContext methods as well, so So I have to write:
with(BuildingContext(building)) {
with(AlwaysSearchByNameV2(building)) {
val toilet = "Toilet".find()
val randomRoom = "123".findById()
}
}
The question is - How I reduce multiple with clauses in this case?
In the example above there are only 2 with clauses, but it's only basic example. In real world there could be dozens of them, and writing with(with(with(with(with... would surely be a pain.
On the side note this doesn't work:
with(BuildingContext(building), AlwaysSearchByNameV2(building)) {
val toilet = "Toilet".find()
val randomRoom = "123".findById()
}
nor this
with(*arrayOf(BuildingContext(building), BuildingContext(building))) {
val toilet = "Toilet".find()
val randomRoom = "123".findById()
}
You can write custom scoping functions instead of relying on with all the time. For example you can add an extension function that will run a block of code in scope of AlwaysSearchByNameV2 object:
inline fun BuildingContext.byName(f : AlwaysSearchByNameV2.() -> Unit) = AlwaysSearchByNameV2(building).apply(f)
And use it:
with(BuildingContext(building)) { // this: BuildingContext
byName { // this: AlwaysSearchByNameV2
val toilet = "Toilet".find()
val randomRoom = "123".findById() // can still refer to BuildingContext
}
// back to this: BuildingContext
}