Custom viewgroup is not showing its child custom views

Question

The draggablepointviews in pathview arent showing up. I did addView in PathView but the pointviews are still not being rendered. Am I missing something? I thought addView was enough and would make the childs render.

PathView.kt

class PathView(context: Context) : ViewGroup(context)
{
    private val pointA = DraggablePointView(context)
    private val pointB = DraggablePointView(context)

    private val paint = Paint().apply {
        strokeWidth = 15f
        color = Color.WHITE
    }

    init
    {
        pointA.x = 50f
        pointA.y = 50f
        pointB.x = 330f
        pointB.y = 330f
        addView(pointA, 100, 100)
        addView(pointB, 100, 100)
        setWillNotDraw(false)
    }

    override fun onDraw(canvas: Canvas?)
    {
        if (canvas == null)
            return

        // Draw a line between pointA and pointB
        canvas.drawLine(pointA.x, pointA.y, pointB.x, pointB.y, paint)
    }

    override fun onLayout(changed: Boolean, l: Int, t: Int, r: Int, b: Int)
    {
    }
}

DraggablePointView.kt

class DraggablePointView(context: Context) : ImageView(context)
{
    init
    {
        setImageResource(R.drawable.point)
        setWillNotDraw(false)
    }

    override fun onDragEvent(event: DragEvent?): Boolean
    {
        println("DRAG EVENT")
        if (event == null)
            return false
        x = event.x
        y = event.y
        return true
    }
}

Then:

val pathView = PathView(context)
frameLayout.addView(pathView)

Answer 1

1) Draw the line

To force a view to draw, call invalidate() .

void invalidate()

Invalidate the whole view. If the view is visible, onDraw(android.graphics.Canvas) will be called at some point in the future.

void invalidate (int l, int t, int r, int b)

Mark the area defined by the rect (l, t, r, b) as needing to be drawn. The coordinates of the dirty rect are relative to the view. If the view is visible, onDraw(android.graphics.Canvas) will be called at some point in the future.

2) Draw the points

Since you extend ViewGroup you're responsible for measuring and laying out the child views.

Perhaps you should extend AbsoluteLayout instead, which already has the measurement and layout logic programmed. Then you can set the coordinates like so:

val lp = layoutParams as AbsoluteLayout.LayoutParams
lp.x = event.x
lp.y = event.y
requestLayout()

Or perhaps you should extend View and draw the points in the same fashion as the line. That should be most efficient. You don't need child views to draw, you need just canvas.

• Override onTouchEvent to listen for and react to touch.
• Draw the drawable to canvas by calling setBounds (tell it where to draw) and draw .