getChildDrawingOrder called/used erratically?

Question

I am creating an isometric map with simple tiles, and I’ve extended RelativeLayout to create a layout that holds these tiles. Really, just using a R

Answer 1

Here is a simple example that shows how to override getChildDrawingOrder

1. as a way to adjust which of the children gets drawn in which order (with the last on being on top)
2. have the order change from a tap/click event

The RelativeLayout class:

public class AlternatingChildDrawingOrderRelativeLayout extends RelativeLayout {

    // the childDrawingOrder modifier
    private int childDrawingOrderModifier = 0;

    public AlternatingChildDrawingOrderRelativeLayout(Context context) {
        super(context);
        init(context);
    }

    void init(Context context) {
        setClickable(true);
        setChildrenDrawingOrderEnabled(true);
        setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                // increment to adjust the child drawing order
                childDrawingOrderModifier++;
                // call invalidate to redraw with new order modifier
                ViewCompat.postInvalidateOnAnimation(v);
            }
        });
    }

    @Override
    protected int getChildDrawingOrder(int childCount, int i) {
        // increment i with the modifier, then afford for out of bounds using modulus of the child count
        int returnValue = (i + childDrawingOrderModifier) % childCount;
        Log.v(VIEW_LOG_TAG, "getChildDrawingOrder returnValue=" + returnValue + " i=" + i);
        return returnValue;
    }

    public AlternatingChildDrawingOrderRelativeLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public AlternatingChildDrawingOrderRelativeLayout(Context context,
                                                      AttributeSet attrs,
                                                      int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    @RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)
    public AlternatingChildDrawingOrderRelativeLayout(Context context,
                                                      AttributeSet attrs,
                                                      int defStyleAttr,
                                                      int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
        init(context);
    }

}

The xml layout

What it looks like

Pictured on the left is the starting drawing order, which is the default based on the xml layout:

Red = index 0
Green = index 1
Blue = index 2  

So from first to last (or think bottom to top) that is: Red, Green, Blue. Here is the log dump of getChildDrawingOrder being called

V/View: getChildDrawingOrder returnValue=0 i=0
V/View: getChildDrawingOrder returnValue=1 i=1
V/View: getChildDrawingOrder returnValue=2 i=2

In the middle, after our first tap, the order changes to Green, Blue, Red

V/View: getChildDrawingOrder returnValue=1 i=0
V/View: getChildDrawingOrder returnValue=2 i=1
V/View: getChildDrawingOrder returnValue=0 i=2

And, on the right side shows us what it looks like after our second tap since the order change to: Blue, Red, Green.

V/View: getChildDrawingOrder returnValue=2 i=0
V/View: getChildDrawingOrder returnValue=0 i=1
V/View: getChildDrawingOrder returnValue=1 i=2

Any tap after this pretty much loops it back to the original order where blue was last to be drawn due to the modulus calculation

HTHs!