Skeleton for VisibilityTracker

VisibilityTracker.java

public class VisibilityTracker {
    private WeakHashMap<View, TrackingInfo> mTrackedViews = new WeakHashMap<>();
    private ViewTreeObserver.OnPreDrawListener mOnPreDrawListener;

    public interface VisibilityTrackerListener {
        void onVisibilityChanged(List<View> visibleViews, List<View> invisibleViews);
    }

    static class TrackingInfo {
        View mRootView;
        int mMinVisiblePercent;
    }

    public VisibilityTracker(Activity activity) {
        View rootView = activity.getWindow().getDecorView();
        ViewTreeObserver viewTreeObserver = rootView.getViewTreeObserver();

        if (viewTreeObserver.isAlive()) {
            mOnPreDrawListener = new ViewTreeObserver.OnPreDrawListener() {
                @Override
                public boolean onPreDraw() {
                    scheduleVisibilityCheck();
                    return true;
                }
            };
            viewTreeObserver.addOnPreDrawListener(mOnPreDrawListener);
        } else {
            Log.d(VisibilityTracker.class.getSimpleName(), "Visibility tracker root view is not alive");
        }
    }

    private void scheduleVisibilityCheck() {
        // TODO:
    }

}