用kotlin语言自定义个五角星view

以下是一个用Kotlin语言自定义的五角星View的示例：

import android.content.Context
import android.graphics.Canvas
import android.graphics.Paint
import android.util.AttributeSet
import android.view.View

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

    private val paint = Paint()
    private var starSize = 0f
    private var starColor = 0

    init {
        paint.isAntiAlias = true
        paint.style = Paint.Style.FILL
        val typedArray = context.obtainStyledAttributes(attrs, R.styleable.StarView)
        starSize = typedArray.getDimension(R.styleable.StarView_starSize, 0f)
        starColor = typedArray.getColor(R.styleable.StarView_starColor, 0)
        typedArray.recycle()
    }

    override fun onDraw(canvas: Canvas?) {
        super.onDraw(canvas)
        canvas?.let {
            val centerX = width / 2f
            val centerY = height / 2f
            val outerRadius = starSize / 2f
            val innerRadius = outerRadius / 2.63f
            val rotationAngle = Math.PI / 2
            val points = arrayOf(
                Pair(centerX, centerY - outerRadius),
                Pair(centerX + innerRadius * Math.cos(rotationAngle).toFloat(), centerY - innerRadius * Math.sin(rotationAngle).toFloat()),
                Pair(centerX + outerRadius * Math.cos(rotationAngle / 2).toFloat(), centerY - outerRadius * Math.sin(rotationAngle / 2).toFloat()),
                Pair(centerX + innerRadius * Math.cos(rotationAngle / 2 * 3).toFloat(), centerY - innerRadius * Math.sin(rotationAngle / 2 * 3).toFloat()),
                Pair(centerX + outerRadius * Math.cos(rotationAngle * 2).toFloat(), centerY - outerRadius * Math.sin(rotationAngle * 2).toFloat()),
                Pair(centerX, centerY + innerRadius),
                Pair(centerX - outerRadius * Math.cos(rotationAngle * 2).toFloat(), centerY - outerRadius * Math.sin(rotationAngle * 2).toFloat()),
                Pair(centerX - innerRadius * Math.cos(rotationAngle / 2 * 3).toFloat(), centerY - innerRadius * Math.sin(rotationAngle / 2 * 3).toFloat()),
                Pair(centerX - outerRadius * Math.cos(rotationAngle / 2).toFloat(), centerY - outerRadius * Math.sin(rotationAngle / 2).toFloat()),
                Pair(centerX - innerRadius * Math.cos(rotationAngle).toFloat(), centerY - innerRadius * Math.sin(rotationAngle).toFloat())
            )
            paint.color = starColor
            canvas.drawVertices(
                Canvas.VertexMode.TRIANGLE_FAN,
                points.size,
                points.flatMap { listOf(it.first, it.second) }.toFloatArray(),
                0,
                null,
                0,
                null,
                0,
                null,
                0,
                0,
                paint
            )
        }
    }

    fun setStarSize(starSize: Float) {
        this.starSize = starSize
        invalidate()
    }

    fun setStarColor(starColor: Int) {
        this.starColor = starColor
        invalidate()
    }
}

这个自定义View继承自Android中的View类，并覆盖了onDraw方法来绘制五角星。

在构造函数中初始化了一个Paint对象，并从属性集中读取了星星的大小和颜色。在onDraw方法中，我们首先计算了五角星的十个点的坐标，然后使用Canvas.drawVertices方法来绘制五角星。

最后，我们在自定义View中提供了两个setter方法，可以动态地改变星星的大小和颜色。