Android and ArrayLIst Size returns 0

Question

Strange problem I'm having here. I add to an arraylist when the user clicks on the view. I get the position and add it to an ArrayList of coordinates. I then draw a circle on the canvas where the coordinates says to do so. The Size check in onDraw always returns 0.

private static ArrayList<Coordinate> coords = new ArrayList<Coordinate>();

OnTouchEvent

...
case MotionEvent.ACTION_POINTER_UP: {
    mLastTouchX = event.getX();
    mLastTouchY = event.getY();
    this.coords.add(new Coordinate(mLastTouchX, mLastTouchY));
    break;
...

OnDraw

protected void onDraw(Canvas canvas) {

    super.onDraw(canvas);
    for(int i = 0; i < this.coords.size(); i++) {
        canvas.drawCircle(coords.get(i).x, coords.get(i).y, 30.0f, mPaint);
    }
}

@veer See the comments on my post, his issue appears to be that onDraw is only called once at init, so it never updates with the new coordinates — Alex Coleman
– Alex Coleman, Commented Aug 24, 2012 at 5:29

Alex Coleman · Accepted Answer · 2012-08-24 05:20:40Z

1

How are you expecting to get a static field with this ? But assuming that's just some typo, try adding some logging:

case MotionEvent.ACTION_POINTER_UP: {
    mLastTouchX = event.getX();
    mLastTouchY = event.getY();
    this.coords.add(new Coordinate(mLastTouchX, mLastTouchY));
    System.out.println("Added a coordinate; new size: " + coords.size());//to see if we are adding it
    break;

And in your onDraw:

System.out.println(coords);//Just to see what all is in it
for(int i = 0; i < this.coords.size(); i++) {
    canvas.drawCircle(coords.get(i).x, coords.get(i).y, 30.0f, mPaint);
}

answered Aug 24, 2012 at 5:20

Alex Coleman

7,3361 gold badge24 silver badges31 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

obataku Over a year ago

You can access static methods via an instance.

lostdev Over a year ago

Seems like onDraw isn't being called continuously ... when printing coords, I get an empty list. This print occurs one time.

Alex Coleman Over a year ago

Ah, yes, was thinking it was flipped. On a different note that, you should probably use the class's name, not this (ex. ClassName.coords, not this.coords)

Alex Coleman Over a year ago

@lostdev Are their any other methods that you can override that have to do with painting? I'm not familiar with the android API, but it appears that's the issue (that it's only called once to init)

lostdev Over a year ago

My understanding of the Android onDraw() is that its called cyclically. This doesn't seem to be the case. It maybe helpful to know the Class extends View.

|

Collectives™ on Stack Overflow

Android and ArrayLIst Size returns 0

1 Answer 1

8 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

8 Comments

Your Answer

Sign up or log in

Post as a guest

Related