Hi guys, I have a question on the sample SpaceXNew...

# multiplatform

[Hee Fan]

Hi guys, I have a question on the sample SpaceXNews App that KMM doc provides. The tutorial link is here Create a multiplatform app using Ktor and SQLDelight, source code is on github,

I got a crash on iOS App when I try to test on SwiftUI. The crash happens on RocketLaunchRow_Previews when I try to make a mockRocketLaunch.
It seems the mockRocketLaunch can not be initialised. From the crash log, I think it might be native memory model issue, however, I could not get useful information to find out the root cause. Could anyone provide more information on the crash? Thanks.

// Crash Log 
1   libsystem_pthread.dylib       	       0x1af25a1e8 pthread_kill + 256
2   libsystem_c.dylib             	       0x180129e28 abort + 124
3   shared                        	       0x106ad9924 konan::abort() + 12
4   shared                        	       0x106ae791c (anonymous namespace)::terminateWithUnhandledException(ObjHeader*)::$_1::operator()() const + 20
5   shared                        	       0x106ae77e0 void (anonymous namespace)::$_0::operator()<(anonymous namespace)::terminateWithUnhandledException(ObjHeader*)::$_1>((anonymous namespace)::terminateWithUnhandledException(ObjHeader*)::$_1) + 80
6   shared                        	       0x106ae75a0 (anonymous namespace)::terminateWithUnhandledException(ObjHeader*) + 56
7   shared                        	       0x106ae7530 (anonymous namespace)::processUnhandledException(ObjHeader*) + 100
8   shared                        	       0x106ae93d4 kotlin::ProcessUnhandledException(ObjHeader*) + 60
9   shared                        	       0x106aeccb4 Kotlin_ObjCExport_trapOnUndeclaredException + 36
10  shared                        	       0x106a96e9c objc2kotlin.1298 + 424 (/<compiler-generated>:1)
11  RocketLaunchRow.1.preview-thunk.dylib	       0x114f2f268 @nonobjc SharedRocketLaunch.init(flightNumber:missionName:launchDateUTC:details:launchSuccess:links:) + 220
12  RocketLaunchRow.1.preview-thunk.dylib	       0x114f2dd58 SharedRocketLaunch.__allocating_init(flightNumber:missionName:launchDateUTC:details:launchSuccess:links:) + 120
13  RocketLaunchRow.1.preview-thunk.dylib	       0x114f2da74 static RocketLaunchRow_Previews.__preview__previews.getter + 940 (RocketLaunchRow.swift:53)
14  iosApp                        	       0x1049817c8 protocol witness for static PreviewProvider.previews.getter in conformance RocketLaunchRow_Previews + 12
15

Source Code

// iosApp/iosApp/RocketLaunchRow.swift
import SwiftUI
import shared

struct RocketLaunchRow: View {
    var rocketLaunch: RocketLaunch
    
    var body: some View {
        HStack {
            VStack(alignment: .leading, spacing: 10.0) {
                Text("hello world")
            }
            Spacer()
        }
    }
}


extension RocketLaunchRow {
    private var launchText: String {
        if let isSuccess = rocketLaunch.launchSuccess {
            return isSuccess.boolValue ? "Successful" : "Unsuccessful"
        } else {
            return "No data"
        }
    }

    private var launchColor: Color {
        if let isSuccess = rocketLaunch.launchSuccess {
            return isSuccess.boolValue ? Color.green : Color.red
        } else {
            return Color.gray
        }
    }
}


struct RocketLaunchRow_Previews: PreviewProvider {
    static var previews: some View {
        let links = Links(patch: nil, article: "article")

        let mockRocketLaunch = RocketLaunch(flightNumber: 1,
                                            missionName: "Mars",
                                            launchDateUTC: "UTC+8",
                                            details: "Details",
                                            launchSuccess: true,
                                            links: links)



    }
}

[Kevin S]

What does RocketLaunch looks like? Is it a data class or more complex?

[Hee Fan]

Hi @Kevin S, it’s defined here,

shared/src/commonMain/kotlin/com/jetbrains/handson/kmm/shared/entity/Entity.kt

package com.jetbrains.handson.kmm.shared.entity

import kotlinx.datetime.TimeZone
import kotlinx.datetime.toInstant
import kotlinx.datetime.toLocalDateTime
import kotlinx.serialization.SerialName
import kotlinx.serialization.Serializable

@Serializable
data class RocketLaunch(
    @SerialName("flight_number")
    val flightNumber: Int,
    @SerialName("name")
    val missionName: String,
    @SerialName("date_utc")
    val launchDateUTC: String,
    @SerialName("details")
    val details: String?,
    @SerialName("success")
    val launchSuccess: Boolean?,
    @SerialName("links")
    val links: Links
) {
    var launchYear = launchDateUTC.toInstant().toLocalDateTime(TimeZone.UTC).year
}

@Serializable
data class Links(
    @SerialName("patch")
    val patch: Patch?,
    @SerialName("article")
    val article: String?
)

@Serializable
data class Patch(
    @SerialName("small")
    val small: String?,
    @SerialName("large")
    val large: String?
)

[Kevin S]

The issue is with launchYear, since that variable is generated when the class is created, it’s using the kotlinx datetime package when running the preview, which is not allowed. You could instead replace it with a getter, such as:

val launchYear:Int
        get() = launchDateUTC.toInstant().toLocalDateTime(TimeZone.UTC).year

That should work since it’s not using the kotlinx library until it needs to. It should work as long as you don’t reference that variable from the preview code.

[Hee Fan]

That’s beautiful answer. Thanks so much.