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    override fun onTouchEvent(event: MotionEvent): Boolean {
        return if (gestureDetector.onTouchEvent(event))
            true
        else
            super.onTouchEvent(event)
    }

    override fun onDown(event: MotionEvent): Boolean {
        return true
    }

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package geva.oren.rotaryknobdemo

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import kotlinx.android.synthetic.main.activity_main.*

class MainActivity : AppCompatActivity(), RotaryKnobView.RotaryKnobListener {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)

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    <geva.oren.rotaryknobdemo.RotaryKnobView
        android:id="@+id/knob"
        class="geva.oren.rotaryknobdemo.RotaryKnobView"
        android:layout_width="@dimen/knob_width"
        android:layout_height="@dimen/knob_height"
        android:layout_marginBottom="312dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"

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    private fun setKnobPosition(angle: Float) {
        val matrix = Matrix()
        knobImageView.scaleType = ScaleType.MATRIX
        matrix.postRotate(angle, width.toFloat() / 2, height.toFloat() / 2)
        knobImageView.imageMatrix = matrix
    }

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    private fun calculateAngle(x: Float, y: Float): Float {
        val px = (x / width.toFloat()) - 0.5
        val py = ( 1 - y / height.toFloat()) - 0.5
        var angle = -(Math.toDegrees(atan2(py, px)))
            .toFloat() + 90
        if (angle > 180) angle -= 360
        return angle
    }

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    interface RotaryKnobListener {
        fun onRotate(value: Int)
    }

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    init {
        this.maxValue = maxValue + 1

        LayoutInflater.from(context)
            .inflate(R.layout.rotary_knob_view, this, true)

        context.theme.obtainStyledAttributes(
            attrs,
            R.styleable.RotaryKnobView,
            0,

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class RotaryKnobView @JvmOverloads constructor(
    context: Context, attrs: AttributeSet? = null, defStyleAttr: Int = 0
) : RelativeLayout(context, attrs, defStyleAttr), GestureDetector.OnGestureListener {
    private val gestureDetector: GestureDetectorCompat
    private var maxValue = 99
    private var minValue = 0
    var listener: RotaryKnobListener? = null
    var value = 50
    private var knobDrawable: Drawable? = null
    private var divider = 300f / (maxValue - minValue)

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    override fun onScroll(e1: MotionEvent, e2: MotionEvent, distanceX: Float, distanceY: Float)
            : Boolean {

        val rotationDegrees = calculateAngle(e2.x, e2.y)
        // use only -150 to 150 range (knob min/max points
        if (rotationDegrees >= -150 && rotationDegrees <= 150) {
            setKnobPosition(rotationDegrees)

            // Calculate rotary value
            // The range is the 300 degrees between -150 and 150, so we'll add 150 to adjust the

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    override fun onScroll(e1: MotionEvent, e2: MotionEvent, distanceX: Float, distanceY: Float)
            : Boolean {
        return true
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        return if (gestureDetector.onTouchEvent(event))
            true
        else
            super.onTouchEvent(event)