如何包裹List< Int>与科特林 [英] How to parcel List<Int> with kotlin

问题描述

我想通过Bundle将数据类(包含int列表作为属性)传递给其他活动，因此我需要将Parcelable实现添加到我的数据类中. 关于如何打包此属性的任何想法吗?

I want to pass a data class (that contains list of int as a property) to other activity through Bundle and therefore i need to add Parcelable implementation to my data class. any idea about how to parcel this property?

data class Test(val id: Long, val files: List<Int>?) : Parcelable {

constructor(parcel: Parcel) : this(
        parcel.readLong(),
        TODO("files"))

override fun writeToParcel(parcel: Parcel, flags: Int) {
    parcel.writeLong(id)
}

override fun describeContents(): Int {
    return 0
}

companion object CREATOR : Parcelable.Creator<Test> {
    override fun createFromParcel(parcel: Parcel): Test {
        return Test(parcel)
    }

    override fun newArray(size: Int): Array<Test?> {
        return arrayOfNulls(size)
    }
}

推荐答案

您可以将整数列表写为int[]:

You can write a list of integers as int[]:

parcel.writeIntArray(files.toIntArray())

确保回读时使用相同的数据结构:

Make sure you use the same data structure when reading back:

files = parcel.createIntArray().toList()

您可以通过跳过数组表示法来使用扩展功能来提高效率:

You could make it more efficient using extension functions by skipping the array representation:

parcel.writeIntList(files)
files = parcel.createIntList()

fun Parcel.writeIntList(input:List<Int>) {
    writeInt(input.size) // Save number of elements.
    input.forEach(this::writeInt) // Save each element.
}

fun Parcel.createIntList() : List<Int> {
    val size = readInt()
    val output = ArrayList<Int>(size)
    for (i in 0 until size) {
        output.add(readInt())
    }
    return output
}

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