实现放射线效果

效果图

xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:elevation="0dp"
    android:gravity="center"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <View
        android:id="@+id/view"
        android:layout_width="200dp"
        android:layout_height="200dp" />

</LinearLayout>

code

findViewById<View>(R.id.view).background = RadiateLightsDrawable()

/**
 * 放射线
 */
private const val START_COLOR: Int = 0xffff0000.toInt()
private const val END_COLOR: Int = 0x00ff0000
class RadiateLightsDrawable : Drawable() {
    private val mPaint = Paint(Paint.ANTI_ALIAS_FLAG)
    private val mTempRect = RectF()
    private val mAreaCount = 16
    private val mSingleAreaAngle = 360f / mAreaCount
    private val mSweepAngle = mSingleAreaAngle / 2
    private val mStartAngle = -mSweepAngle / 2

    init {
        mPaint.style = Paint.Style.FILL
        mPaint.alpha = (255 * 0.5).toInt()
    }

    override fun draw(canvas: Canvas) {
        canvas.save()
        val centerX = canvas.width / 2f
        val centerY = canvas.height / 2f
        val radius = min(centerX, centerY)
        mTempRect.set(centerX - radius, centerY - radius, centerX + radius, centerY + radius)
        mPaint.shader = LinearGradient(centerX, centerY, centerX + radius, centerY, START_COLOR, END_COLOR, Shader.TileMode.CLAMP)
        for (i in (0 until mAreaCount)) {
            canvas.drawArc(mTempRect, mStartAngle, mSweepAngle, true, mPaint)
            canvas.rotate(mSingleAreaAngle, centerX, centerY)
        }
        canvas.restore()
    }

    override fun setAlpha(alpha: Int) {
    }

    override fun getOpacity(): Int {
        return PixelFormat.OPAQUE
    }

    override fun setColorFilter(colorFilter: ColorFilter?) {
    }
}