2D Array in Kotlin | 易学教程

问题

How do you make a 2D Int array in Kotlin? I'm trying to convert this code to Kotlin:

    int[][] states = new int[][] {
        new int[]{-android.R.attr.state_pressed}, // not pressed
        new int[] { android.R.attr.state_pressed}  // pressed
    };
    int[] colors = new int[] {
        foregroundColor,
        accentColor,
        accentColor
    };
    ColorStateList myList = new ColorStateList(states, colors);

Here is one attempt I tried, where the first 2D array didn't work, but I got the 1D array to work:

    //This doesn't work:
    var states: IntArray = intArrayOf(
        intArrayOf(-android.R.attr.state_pressed), // not pressed
        intArrayOf(android.R.attr.state_pressed)  // pressed
    );
    //This array works:
    var colors: IntArray = intArrayOf(
        foregroundColor,
        accentColor,
        accentColor
    );
    val myList: ColorStateList = ColorStateList(states, colors);

回答1:

You are trying to put your IntArrays inside another array to make it 2-dimensional. The type of that array cannot be intArray, which is why this fails. Wrap your initial arrays with arrayOf instead of intArrayOf.

val even: IntArray = intArrayOf(2, 4, 6)
val odd: IntArray = intArrayOf(1, 3, 5)

val lala: Array<IntArray> = arrayOf(even, odd)

回答2:

You may use this line of code for an Integer array.

val array = Array(row) { IntArray(column) }

This line of code is pretty simple and works like 1D array and also can be accessible like java 2D array.

回答3:

Short Answer:

// A 6x5 array of Int, all set to 0.
var m = Array(6) {Array(5) {0} }

Here is another example with more details on what is going on:

// a 6x5 Int array initialise all to 0
var m = Array(6, {i -> Array(5, {j -> 0})})

The first parameter is the size, the second lambda method is for initialisation.

回答4:

I have been using this one-liner when creating matrix

var matrix: Array<IntArray> = Array(height) { IntArray(width) }

回答5:

1. Nested arrayOf calls

You can nest calls of arrayOf, e.g., to create an Array of IntArray, do the following:

val first: Array<IntArray> = arrayOf(
    intArrayOf(2, 4, 6),
    intArrayOf(1, 3, 5)
)

Note that the IntArray itself only takes arguments of type Int as arguments, so you cannot have an IntArray<IntArray> which obviously does not make much sense anyway.

2. Use Array::constructor(size: Int, init: (Int) -> T) for repeated logic

If you want to create your inner arrays with some logical behaviour based on the index, you can make use of the Array constructor taking a size and an init block:

val second: Array<IntArray> = Array(3) {
    intArrayOf(it * 1, it * 2, it * 3, it * 4)
} 
//[[0, 0, 0, 0], [1, 2, 3, 4], [2, 4, 6, 8]]

回答6:

It seems that you are trying to create a ColorStateList in Kotlin. The code for that is a bit messy, i'll try to keep it readable:

val resolvedColor = Color.rgb(214, 0, 0)
val states = arrayOf(
    intArrayOf(-android.R.attr.state_pressed),
    intArrayOf(android.R.attr.state_pressed)
)

val csl = ColorStateList(
    states,
    intArrayOf(resolvedColor, Color.WHITE)
)

回答7:

Using an inline function and a Pair:

  inline fun<reified T> Pair<Int,Int>.createArray(initialValue:T) = Array(this.first){ Array(this.second){initialValue}}

  // Create m*n Array of Ints filled with 0
  val twoDimArray = Pair(10,20).createArray(0)

  // Create m*n Array of Doubles filled with 0.0
  val twoDimArray = Pair(10,20).createArray(0.0)

  // Create m*n Array of Strings filled with "Value"
  val twoDimArray = Pair(10,20).createArray("Value")

  ...

回答8:

You can use a simple 1D (linear) array for this purpose. For example, this is my class for a rectangle array of Double values:

/**
 * Rect array of Double values
 */
class DoubleRectArray(private val rows: Int, private val cols: Int) {
    private val innerArray: DoubleArray

    init {
        if(rows < 1) {
            throw IllegalArgumentException("Rows value is invalid. It must be greater than 0")
        }

        if(cols < 1) {
            throw IllegalArgumentException("Cols value is invalid. It must be greater than 0")
        }

        innerArray = DoubleArray(rows*cols)
    }

    /**
     *
     */
    fun get(row: Int, col: Int): Double {
        checkRowAndCol(row, col)
        return innerArray[row*cols + col]
    }

    /**
     *
     */
    fun set(row: Int, col: Int, value: Double) {
        checkRowAndCol(row, col)
        innerArray[row*cols + col] = value
    }

    /**
     *
     */
    private fun checkRowAndCol(row: Int, col: Int) {
        if(row !in 0 until rows) {
            throw ArrayIndexOutOfBoundsException("Row value is invalid. It must be in a 0..${rows-1} interval (inclusive)")
        }

        if(col !in 0 until cols) {
            throw ArrayIndexOutOfBoundsException("Col value is invalid. It must be in a 0..${cols-1} interval (inclusive)")
        }
    }
}

回答9:

You can create two one dimensional array and add them in new array.

val unChecked = intArrayOf(-android.R.attr.state_checked)
val checked = intArrayOf(android.R.attr.state_checked)
val states = arrayOf(unChecked, checked)

val thumbColors = intArrayOf(Color.WHITE, Color.parseColor("#55FFD4"))
val stateList = ColorStateList(states, thumbColors)

来源：https://stackoverflow.com/questions/34145495/2d-array-in-kotlin

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arrays

kotlin