Android Vertical Custom ViewGroup

Question

I have a simple problem. I'm extending ViewGroup, and I want to align buttons to the right side of the screen from top-to-bottom. Problem is, nothing shows up on my screen. I've confirmed it's not a problem with anything else, only my onLayout() overriden method. Could you help me out?

Code in question:

    final int count = getChildCount();
    int curWidth, curHeight, curLeft, curTop;

    //get the available size of child view
    int childLeft = this.getPaddingLeft();
    int childTop = this.getPaddingTop();
    int childRight = this.getMeasuredWidth() - this.getPaddingRight();
    int childBottom = this.getMeasuredHeight() - this.getPaddingBottom();
    int childWidth = childRight - childLeft;
    int childHeight = childBottom - childTop;

    curTop = childTop;
    for (int i = 0; i < count; i++) {
        View child = getChildAt(i);

        //Get the maximum size of the child
        child.measure(MeasureSpec.makeMeasureSpec(childWidth, MeasureSpec.AT_MOST),
                MeasureSpec.makeMeasureSpec(childHeight, MeasureSpec.AT_MOST));
        curWidth = child.getMeasuredWidth();
        curHeight = child.getMeasuredHeight();

        child.layout(getMeasuredWidth() - getPaddingRight() - curWidth,
                curTop, getMeasuredWidth() - getPaddingRight(), curTop - curHeight);
        curTop -= childHeight;
    }

I've added a few LOG statements to my code, and what I have is frankly infuriating.

07-11 14:46:46.321  32172-32172/milespeele.canvas D/Miles﹕ LEFT: 912
07-11 14:46:46.322  32172-32172/milespeele.canvas D/Miles﹕ TOP: 1008
07-11 14:46:46.322  32172-32172/milespeele.canvas D/Miles﹕ RIGHT: 1080
07-11 14:46:46.322  32172-32172/milespeele.canvas D/Miles﹕ BOTTOM: 1008

These are all valid coordinates (for one button) given the dimensions of my phone's creen, but no buttons are appearing.

Answer 1

I didn't scan this completely, but I see you have curTop - curHeight as last parameter in child.layout(). Should it be curTop + curHeight?

Answer 2

You are decrementing curTop. Coordinate values increase going down the screen, so you are actually layout out children off screen above the top of the ViewGroup. I think you want curTop + curHeight as the last argument of child.layout(), and i think the last line should be curTop += curHeight.

As an aside, you really should not be measuring children in onLayout(). That's what onMeasure() is for.

Answer 3

Solved. Thanks for those that answered.

It seemed the problem was I misunderstood android's coordinate system.

Working code: (where l & r are parameters of onLayout())

    final int count = getChildCount();

    int left = (int) (l + getMeasuredWidth() - buttonMargin - buttonWidth);
    int right = (int) (r - buttonMargin);

    int currentTop = (int) (t + buttonMargin);
    for (int i = 0; i < count; i++) {
        View child = getChildAt(i);
        child.layout(left, currentTop, right, currentTop + buttonHeight);
        currentTop += buttonHeight + buttonMargin;
    }