左右滑动时动作

Question

I have trouble with coding a swipe listener that would start a function. But I don't want to use fragments.

Here's the code:

class Dock : AppCompatActivity(), GestureDetector.OnGestureListener
{
    override fun onCreate(savedInstanceState: Bundle?)
    {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.dock)
        hide_bars()
    }

    private val swipeThreshold = 100
    private val swipeVelocityThreshold = 100

    override fun onFling(downEvent: MotionEvent, moveEvent: MotionEvent, velocityX: Float, velocityY: Float): Boolean
    {
        var result = false
        val diffY = moveEvent.y - downEvent.y
        val diffX = moveEvent.x - downEvent.x
        if (Math.abs(diffX) > Math.abs(diffY))
        {
            // right or left swipe
            if (Math.abs(diffX) > swipeThreshold && Math.abs(velocityX) > swipeVelocityThreshold)
            {
                if (diffX > 0)
                {
                    swipeRight()
                } else
                {
                    swipeLeft()
                }
                result = true
            }
        } else
        {
            // up or down swipe
            if (Math.abs(diffY) > swipeThreshold && Math.abs(velocityY) > swipeVelocityThreshold)
            {
                if (diffY > 0)
                {
                    swipeDown()
                } else
                {
                    swipeUp()
                }
                result = true
            }
        }
        return result
    }

    private fun swipeUp()
    {
        Toast.makeText(this, "Swipe Top", Toast.LENGTH_LONG).show()
    }

    private fun swipeDown()
    {
        Toast.makeText(this, "Swipe Bottom", Toast.LENGTH_LONG).show()
    }

    private fun swipeLeft()
    {
        Toast.makeText(this, "Swipe Left", Toast.LENGTH_LONG).show()
    }

    private fun swipeRight()
    {
        Toast.makeText(this, "Swipe Right", Toast.LENGTH_LONG).show()
    }

I can start the app with no problem, however, when I swipe, nothing changes. No toasts, no activity started that would change the layout. That's why I'm here. Please help me.

"After swipe" functions are not comprised in the code, because they are not the problem (tested) and this post couldn't be created.

Answer 1

Activities don't receive touch input. Views do. You'd need to set the onTouchListener of some view within your app to implement this behavior. In addition, since your app will probably have subviews you can't just put it on the root view alone- you'll have to implement onInterceptTouchEvent as well to steal touch events from the child views when appropriate (please note doing this poorly may break some behavior of child views).