GestureListener.onFling kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter e1 - Android

Question

I am manage onSwipeRight and onSwipeLeft on recyclerView like bellow:

override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
   super.onViewCreated(view, savedInstanceState)
        val swipeController = SwipeController(this)
        val itemTouchhelper = ItemTouchHelper(swipeController)
        itemTouchhelper.attachToRecyclerView(recycler_view)

        recycler_view.setOnTouchListener(object : OnSwipeTouchListener(activity!!) {
            override fun onSwipeLeft() {
                val intent = Intent(activity, MainActivity::class.java)
                intent.putExtra("ONE", 1)
                intent.flags = Intent.FLAG_ACTIVITY_CLEAR_TOP
                startActivity(intent)
                activity!!.finish()
            }

            override fun onSwipeRight() {
        })
}

And my OnSwipeTouchListener.kt:

open class OnSwipeTouchListener(context: Context) : View.OnTouchListener {
    var context: Context? = context

    private val gestureDetector = GestureDetector(context, GestureListener())

    fun onTouch(event: MotionEvent): Boolean {
        return gestureDetector.onTouchEvent(event)
    }

    private inner class GestureListener : GestureDetector.SimpleOnGestureListener() {

        private val SWIPE_THRESHOLD = 100
        private val SWIPE_VELOCITY_THRESHOLD = 100

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

        override fun onSingleTapConfirmed(e: MotionEvent): Boolean {
            onTouch(e)
            return true
        }


        override fun onFling(e1: MotionEvent, e2: MotionEvent, velocityX: Float, velocityY: Float): Boolean {
            val result = false
            try {
                val diffY = e2.y - e1.y
                val diffX = e2.x - e1.x
                if (Math.abs(diffX) > Math.abs(diffY)) {
                    if (Math.abs(diffX) > SWIPE_THRESHOLD && Math.abs(velocityX) > SWIPE_VELOCITY_THRESHOLD) {
                        if (diffX > 0) {
                            onSwipeRight()
                        } else {
                            onSwipeLeft()
                        }
                    }
                } else {
                    // onTouch(e);
                }
            } catch (exception: Exception) {
                exception.printStackTrace()
            }

            return result
        }
    }

    @SuppressLint("ClickableViewAccessibility")
    override fun onTouch(v: View, event: MotionEvent): Boolean {
        return gestureDetector.onTouchEvent(event)
    }

    open fun onSwipeRight() {}

    open fun onSwipeLeft() {}
}

And SwipeController.kt:

internal class SwipeController(private val swipeControllerInter: SwipeControllerInter) : ItemTouchHelper.Callback() {
    private var swipeBack = false

    interface SwipeControllerInter {
        fun left()

        fun right()
    }

    override fun getMovementFlags(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder): Int {
        return makeMovementFlags(0, LEFT or RIGHT)
    }

    override fun onMove(recyclerView: RecyclerView, viewHolder: RecyclerView.ViewHolder, target: RecyclerView.ViewHolder): Boolean {
        return false
    }

    override fun onSwiped(viewHolder: RecyclerView.ViewHolder, direction: Int) {

    }

    override fun convertToAbsoluteDirection(flags: Int, layoutDirection: Int): Int {
        if (swipeBack) {
            swipeBack = false
            return 0
        }
        return super.convertToAbsoluteDirection(flags, layoutDirection)
    }

    override fun onChildDraw(c: Canvas,
                             recyclerView: RecyclerView,
                             viewHolder: RecyclerView.ViewHolder,
                             dX: Float, dY: Float,
                             actionState: Int, isCurrentlyActive: Boolean) {

        if (actionState == ACTION_STATE_SWIPE) {
            if (dX > 0) {
                // then swiping right.
                swipeControllerInter.right()
            } else if (dX < 0) {
                // then swiping left.
                swipeControllerInter.left()
            }
            // If dX == 0 then at at start position.
        } else {
            super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive)
        }

        if (actionState == ACTION_STATE_SWIPE) {
            setTouchListener(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive)
        }
        super.onChildDraw(c, recyclerView, viewHolder, dX, dY, actionState, isCurrentlyActive)
    }

    @SuppressLint("ClickableViewAccessibility")
    private fun setTouchListener(c: Canvas,
                                 recyclerView: RecyclerView,
                                 viewHolder: RecyclerView.ViewHolder,
                                 dX: Float, dY: Float,
                                 actionState: Int, isCurrentlyActive: Boolean) {

        recyclerView.setOnTouchListener { v, event ->
            swipeBack = event.action == MotionEvent.ACTION_CANCEL || event.action == MotionEvent.ACTION_UP
            false
        }
    }

}

But when I see my fireBase I see bellow crash:

Fatal Exception: java.lang.IllegalArgumentException
Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter e1
xx.xx.xx.tools.OnSwipeTouchListener$GestureListener.onFling (OnSwipeTouchListener.kt)

Answer 1

By default all variables and parameters in Kotlin are nonnull. Parameter of the method should be with "?".

 override fun onFling(
            e1: MotionEvent?,
            e2: MotionEvent?,
            velocityX: Float,
            velocityY: Float
        ): Boolean { ...