用Kotlin帮我写一个Android自定义View进度条，进度条颜色是渐变色，宽高可以自行设置

好的，以下是用 Kotlin 编写的 Android 自定义 View 进度条的代码：

class GradientProgressBar(context: Context, attrs: AttributeSet) : View(context, attrs) {

    private var progress = 0f
    private var maxProgress = 100f
    private var barHeight = 10.dpToPx()
    private var barCornerRadius = 5.dpToPx()
    private var barBackgroundColor = Color.GRAY
    private var barGradientColors = intArrayOf(Color.BLUE, Color.GREEN, Color.YELLOW, Color.RED)

    private val backgroundPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
        style = Paint.Style.FILL
        color = barBackgroundColor
    }

    private val gradientPaint = Paint(Paint.ANTI_ALIAS_FLAG).apply {
        style = Paint.Style.FILL
    }

    private val rectF = RectF()

    init {
        val typedArray = context.obtainStyledAttributes(attrs, R.styleable.GradientProgressBar)
        barHeight = typedArray.getDimensionPixelSize(R.styleable.GradientProgressBar_barHeight, barHeight)
        barCornerRadius = typedArray.getDimensionPixelSize(R.styleable.GradientProgressBar_barCornerRadius, barCornerRadius)
        barBackgroundColor = typedArray.getColor(R.styleable.GradientProgressBar_barBackgroundColor, barBackgroundColor)
        barGradientColors = typedArray.getColorArray(R.styleable.GradientProgressBar_barGradientColors) ?: barGradientColors
        typedArray.recycle()
    }

    override fun onMeasure(widthMeasureSpec: Int, heightMeasureSpec: Int) {
        val height = paddingTop + paddingBottom + barHeight
        val width = View.getDefaultSize(suggestedMinimumWidth, widthMeasureSpec)
        setMeasuredDimension(width, height)
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        rectF.set(paddingLeft.toFloat(), paddingTop.toFloat(), (width - paddingRight).toFloat(), (height - paddingBottom).toFloat())

        // Draw background
        canvas.drawRoundRect(rectF, barCornerRadius.toFloat(), barCornerRadius.toFloat(), backgroundPaint)

        // Draw gradient
        val gradient = LinearGradient(rectF.left, rectF.top, rectF.right, rectF.bottom, barGradientColors, null, Shader.TileMode.CLAMP)
        gradientPaint.shader = gradient
        val progressWidth = progress / maxProgress * rectF.width()
        canvas.drawRoundRect(rectF.left, rectF.top, rectF.left + progressWidth, rectF.bottom, barCornerRadius.toFloat(), barCornerRadius.toFloat(), gradientPaint)
    }

    fun setProgress(progress: Float) {
        this.progress = progress
        invalidate()
    }

    fun setMaxProgress(maxProgress: Float) {
        this.maxProgress = maxProgress
        invalidate()
    }

    private fun Int.dpToPx(): Int {
        return TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, this.toFloat(), resources.displayMetrics).toInt()
    }

    private fun TypedArray.getColorArray(@StyleableRes index: Int): IntArray? {
        val resourceId = getResourceId(index, 0)
        return if (resourceId != 0) {
            resources.getIntArray(resourceId).map { Color.parseColor("#$it") }.toIntArray()
        } else {
            null
        }
    }
}

在 XML 中使用时，可以这样：

<com.example.GradientProgressBar
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    app:barBackgroundColor="#CCCCCC"
    app:barGradientColors="@array/gradient_colors"
    app:barHeight="20dp"
    app:barCornerRadius="10dp"/>

其中，`app:barGradientColors` 是一个颜色数组，可以在 `res/values/arrays.xml` 中定义：

<array name="gradient_colors">
    <item>#FF0000</item>
    <item>#FFFF00</item>
    <item>#00FF00</item>
    <item>#0000FF</item>
</array>