如何在kotlin中Parcelize一个MutableList

Question

我有一个应用程序，可以让用户在自定义视图上拖动和绘制方框。我想使用onSavedInstanceState(): Parcelable和onRestoreInstanceState(state: Parcelable)在方向更改期间保持这些框(框的列表(的状态。然而，我不知道如何存储MutableList，因为唯一可用的函数是putParcelableArrayList。请告诉我如何分割一个可变列表以在整个轮换中保持框？我知道医生说这是可能的，但我不知道怎么做。这是代码。

@Parcelize
class Box(private val start: PointF) : Parcelable {
// When a user touches BoxDrawingView, a new box will be created and added to the list of existing boxes.
var end: PointF = start
val left: Float
get() = start.x.coerceAtMost(end.x)
val right: Float
get() = start.x.coerceAtLeast(end.x)
val top: Float
get() = start.y.coerceAtMost(end.y)
val bottom: Float
get() = start.y.coerceAtLeast(end.y)
}

我的自定义视图

import android.content.Context
import android.graphics.Canvas
import android.graphics.Paint
import android.graphics.PointF
import android.os.Bundle
import android.os.Parcelable
import android.util.AttributeSet
import android.util.Log
import android.view.MotionEvent
import android.view.View
/** This Class is where we setup our custom View and write the Implementation for listening to touch events from the USER and draw boxes on the Screen.**/
private const val TAG = "BoxDrawingView"
private const val BOX_STATE = "box"
private const val VIEW_STATE = "view"
class BoxDrawingView(context: Context, attrs: AttributeSet? = null) :
View(context, attrs) {
private var currentBox: Box? = null
private var boxen = mutableListOf<Box>()  // list of boxes to be drawn out on the screen
private val boxPaint = Paint().apply {
color = 0x22ff0000
}
private val backGroundPaint = Paint().apply {
color = 0xfff8efe0.toInt()
}
init {
isSaveEnabled = true
}
override fun onSaveInstanceState(): Parcelable {
val bundle = Bundle()
bundle.putParcelableArrayList(BOX_STATE, boxen)  // type mismatch error because of mutableList passed to ArrayList
bundle.putParcelable(VIEW_STATE, super.onSaveInstanceState())
return bundle
}
override fun onRestoreInstanceState(state: Parcelable?) {
var viewState = state
if (viewState is Bundle) {
boxen = viewState.getParcelableArrayList<Box>(BOX_STATE)?.toMutableList() ?: mutableListOf()
viewState = viewState.getParcelable(VIEW_STATE)
}
super.onRestoreInstanceState(state)
}

override fun onDraw(canvas: Canvas) {
// Fill in the background
canvas.drawPaint(backGroundPaint)
boxen.forEach { box ->
canvas.drawRect(box.left, box.top, box.right, box.bottom, boxPaint)
}
}
override fun onTouchEvent(event: MotionEvent): Boolean {
val current = PointF(event.x, event.y)
var action = ""
when(event.action) {
MotionEvent.ACTION_DOWN -> {
action = "ACTION_DOWN"
// Reset drawing state
currentBox = Box(current).also {
boxen.add(it)
}
}
MotionEvent.ACTION_MOVE -> {
action = "ACTION_MOVE"
// update the currentBox.end as the user moves his/her finger around the screen
updateCurrentBox(current)
}
MotionEvent.ACTION_UP -> {
action = "ACTION_UP"
// tells the last report of the currentBox as the user's finger leaves the screen
updateCurrentBox(current)
currentBox = null
}
MotionEvent.ACTION_CANCEL -> {
action = "ACTION_CANCEL"
currentBox = null
}
}
// this is a log message for each of the 4 Event actions
Log.i(TAG, "$action at x=${current.x}, y=${current.y}")
return true
}

Answer 1

将boxen类型更改为arrayList((成功。事实证明，arrayList是一个隐藏的可变列表。此外，David wasser在评论中的回答也起到了作用。