canvas.drawCircle sometimes working, sometimes not[android help]

canvas.drawCircle sometimes working, sometimes not

I bought the book Programming Android, and it's a little confusing and disappointing on how they have different code in their Github (https://github.com/bmeike/ProgrammingAndroid2Examples/tree/master/AndroidUIDemo) and their book. I'm stuck in an example that teaches how to draw a circle in a random point, with the color that is assigned to the button, like, when I click the RED button, it should draw a red circle in a view.

I did some extra code and somehow I managed to get it working. Here is my onDraw method:

@Override
protected void onDraw(Canvas canvas)
{
paint.setStyle(Style.STROKE);
paint.setColor(hasFocus() ? Color.BLUE : Color.GRAY);
canvas.drawRect(0, 0, getWidth() - 1, getHeight() - 1, paint);

    if (this.points == null) return;

    paint.setStyle(Style.FILL);

    for (Point p : points.getAllPoints())
    {
        paint.setColor(p.getColor());
        canvas.drawCircle(p.getX(), p.getY(), 
                  p.getDiameter(), paint);
    }
}

Sometimes it works, sometimes not, BUT when it works, it draws a thin, large oval shape.

p.getDiameter() is ALWAYS 6. Even if I put it to a fixed 6, the effect is the same.

Also, there is some strange thing happening: If I replace p.getY() and p.getX() by 50, it will never draw anything on the screen. 50 should not be out of the screen bounds.

Unfortunately I can't post a screenshot, my device is not rooted.

Here is some extra relevant code.

Setting the pointView size (the place where I draw points):

@Override
public void onWindowFocusChanged(boolean hasFocus)
{
    super.onWindowFocusChanged(hasFocus);

    pointView.setLayoutParams(new android.widget.LinearLayout.LayoutParams(root.getWidth(), root.getHeight()/2));
}

Add an OnCLickListener to the button, so when I click it, it should draw a circle.

button1.setOnClickListener(new OnClickListener() //I'll not put the Red button here, for the sake of brevity.
    {
        @Override
        public void onClick(View arg0)
        {
            makeDot(pointModel, pointView, Color.GREEN);
        }
    });

And the makeDot method:

private final Random rnd = new Random();
void makeDot(Points points, PointView pointView, int color)
{
    points.addPoint(
            rnd.nextFloat()*pointView.getWidth(),
            rnd.nextFloat()*pointView.getHeight(),
            color, POINT_DIAMETER /*always 6*/);

}

(I think POINT_DIAMETER should be POINT_RADIUS but it's OK for now.)

So, how can I get it to draw a round circle in a random position in the screen?

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