android - 为什么即使初始化了Lateinit属性，我仍会得到kotlin.UninitializedPropertyAccessException(可能)

Question

好的，所以我在如下小部件中声明了lateinit var job。

class TempHumidDisplayWidget : AppWidgetProvider(), CoroutineScope {
    private lateinit var job: Job
    override val coroutineContext: CoroutineContext
        get() = Dispatchers.Main + job
    ...

在onEnabled函数中，我对其进行了初始化:

override fun onEnabled(context: Context) {
    job = Job()
    Log.i("com.github.animeshz", "On enabled")
    ...

在onUpdate函数中，我将使用启动函数，该函数调用coroutineContext的get函数来调度使用作业变量的协程。

override fun onUpdate(
    context: Context,
    appWidgetManager: AppWidgetManager,
    appWidgetIds: IntArray
) {
    // There may be multiple widgets active, so update all of them
    for (appWidgetId in appWidgetIds) {
        launch { updateAppWidget(context, appWidgetManager, appWidgetId) }
    }
}

在logcat内部，出现以下错误:

4425-4425/? I/com.github.animeshz: On enabled
...
2020-05-01 11:06:06.639 4425-4425/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.github.animeshz.shivamwidget, PID: 4425
    java.lang.RuntimeException: Unable to start receiver com.github.animeshz.shivamwidget.TempHumidDisplayWidget: kotlin.UninitializedPropertyAccessException: lateinit property job has not been initialized
        at android.app.ActivityThread.handleReceiver(ActivityThread.java:3183)
        at android.app.ActivityThread.-wrap18(ActivityThread.java)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1636)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:154)
        at android.app.ActivityThread.main(ActivityThread.java:6334)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
     Caused by: kotlin.UninitializedPropertyAccessException: lateinit property job has not been initialized
        at com.github.animeshz.shivamwidget.TempHumidDisplayWidget.getCoroutineContext(TempHumidDisplayWidget.kt:26)
        at kotlinx.coroutines.CoroutineContextKt.newCoroutineContext(CoroutineContext.kt:33)
        at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch(Builders.common.kt:50)
        at kotlinx.coroutines.BuildersKt.launch(Unknown Source)
        at kotlinx.coroutines.BuildersKt__Builders_commonKt.launch$default(Builders.common.kt:47)
        at kotlinx.coroutines.BuildersKt.launch$default(Unknown Source)
        at com.github.animeshz.shivamwidget.TempHumidDisplayWidget.onUpdate(TempHumidDisplayWidget.kt:38)
        at android.appwidget.AppWidgetProvider.onReceive(AppWidgetProvider.java:66)
        at android.app.ActivityThread.handleReceiver(ActivityThread.java:3171)
        at android.app.ActivityThread.-wrap18(ActivityThread.java) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1636) 
        at android.os.Handler.dispatchMessage(Handler.java:102) 
        at android.os.Looper.loop(Looper.java:154) 
        at android.app.ActivityThread.main(ActivityThread.java:6334) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 

It is clear that onEnabled is called before the onUpdate method but the job variable is not initialized somehow, I don't know how to fix or debug it further

在onEnabled函数中实际上未初始化的在onEnabled中初始化的作业变量怎么可能呢？这是错误还是什么？

任何帮助将不胜感激，在此先感谢!

Answer 1

这只是在吐口水，因为我不知道Android中小部件的详细信息，但是这样的方法可能有效:

class TempHumidDisplayWidget : AppWidgetProvider() {
    companion object {
        val jobs = mutableMapOf<Context, Job>()

        fun getScope(context: Context): CoroutineScope {
            val job = jobs[context] ?: throw IllegalStateException("Context $context not enabled currently")
            return object : CoroutineScope { 
                override val coroutineContext: CoroutineContext = Dispatchers.Main + job
                ...
            }
        }
    }

    override fun onEnabled(context: Context) {
        jobs[context] = Job()
        ...
    }

    override fun onDisabled(context: Context) {
        jobs.remove(context)?.cancel()
        ...
    }

    override fun onUpdate(
        context: Context,
        appWidgetManager: AppWidgetManager,
        appWidgetIds: IntArray
    ) {
        val scope = getScope(context)
        for (appWidgetId in appWidgetIds) {
            scope.launch { updateAppWidget(context, appWidgetManager, appWidgetId) }
        }
    }
}

通常，“静态地”保留对 Context的引用是一个坏主意，但这可能是正确的，因为在 onDisabled中已将其删除。或改为使用 WeakHashMap 。