Frame by frame #2

SpinnerLoaderView.java

public class SpinnerLoaderView extends View {
  
    private static final long ANIMATION_DURATION = 1250L;

    private ValueAnimator mAnimator;
    private float mArcStart;
    private float mArcSize;
    
    // ...
  
    @Override
    protected void onAttachedToWindow() {
        super.onAttachedToWindow();
        mAnimator = ValueAnimator.ofFloat(0f, 1f);
        mAnimator.setRepeatMode(ValueAnimator.RESTART);
        mAnimator.setRepeatCount(ValueAnimator.INFINITE);
        mAnimator.setInterpolator(new LinearInterpolator());
        mAnimator.setDuration(ANIMATION_DURATION);
        mAnimator.addUpdateListener(new ValueAnimator.AnimatorUpdateListener() {
            @Override
            public void onAnimationUpdate(ValueAnimator valueAnimator) {
                final float progress = (float) valueAnimator.getAnimatedValue();
                mArcStart = calculateArcStart(progress);
                mArcSize = calculateArcSize(progress);
                invalidate();
            }
        });
        mAnimator.start();
    }

    @Override
    protected void onDetachedFromWindow() {
        super.onDetachedFromWindow();
        mAnimator.cancel();
        mAnimator.removeAllUpdateListeners();
        mAnimator = null;
    }
}