Android 为什么我的LocalDate.parse不能使用从gson插入的值？

我有一门课：

data class Day(val date: String, val events: List<Event>){
    val localDateTimeDate: LocalDate by lazy {
        LocalDate.parse(date)
    }
}

如果有一天我尝试读取

。localDateTimeDate

，我会得到一个nullpointer异常：

2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object kotlin.Lazy.getValue()' on a null object reference
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at nl.joozd.joozdter.data.Day.getLocalDateTimeDate(Unknown Source:25)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at nl.joozd.joozdter.ui.PdfParserActivity$onCreate$$inlined$let$lambda$1.invoke(PdfParserActivity.kt:140)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at nl.joozd.joozdter.ui.PdfParserActivity$onCreate$$inlined$let$lambda$1.invoke(PdfParserActivity.kt:28)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at org.jetbrains.anko.AsyncKt$doAsync$1.invoke(Async.kt:143)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at org.jetbrains.anko.AsyncKt$doAsync$1.invoke(Unknown Source:0)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at org.jetbrains.anko.AsyncKt$sam$java_util_concurrent_Callable$0.call(Unknown Source:2)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:266)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.lang.Thread.run(Thread.java:764)

---

如果一个类没有无参数构造函数，Gson会在不调用构造函数的情况下创建一个对象，因此存储

lazy

delegate的字段不会初始化，并且在访问委托给它的属性时会得到一个NullPointerException

---

有关可能的解决方案，请参见此问题：

谢谢！这会让我重新开始：）我用

val-gsonDaysList=（Gson（）.fromJson（jsonData，listType））

替换为

val-gsonDaysList=（Gson（）.fromJson（jsonData，listType））

val-daysList=gsonDaysList.map{Day（it.date，it.events）}

，但是基本上把gson转储到一个类中，然后我用它来填充另一个类。也许不是最优雅的方式，但它很有效。

2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err: java.lang.NullPointerException: Attempt to invoke interface method 'java.lang.Object kotlin.Lazy.getValue()' on a null object reference
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at nl.joozd.joozdter.data.Day.getLocalDateTimeDate(Unknown Source:25)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at nl.joozd.joozdter.ui.PdfParserActivity$onCreate$$inlined$let$lambda$1.invoke(PdfParserActivity.kt:140)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at nl.joozd.joozdter.ui.PdfParserActivity$onCreate$$inlined$let$lambda$1.invoke(PdfParserActivity.kt:28)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at org.jetbrains.anko.AsyncKt$doAsync$1.invoke(Async.kt:143)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at org.jetbrains.anko.AsyncKt$doAsync$1.invoke(Unknown Source:0)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at org.jetbrains.anko.AsyncKt$sam$java_util_concurrent_Callable$0.call(Unknown Source:2)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.FutureTask.run(FutureTask.java:266)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:301)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1167)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:641)
2019-08-13 00:06:13.075 21870-21942/nl.joozd.joozdter W/System.err:     at java.lang.Thread.run(Thread.java:764)