static View retrieveFromScrap(SparseArray<View> scrapViews, int position) {
		int size = scrapViews.size();
		if (size > 0) {
			// See if we still have a view for this position.
			for (int i = 0; i < size; i++) {
				int fromPosition = scrapViews.keyAt(i);
				View view = scrapViews.get(fromPosition);
				if (fromPosition == position) {
					scrapViews.remove(fromPosition);
					return view;
				}
			}
			int index = size - 1;
			View r = scrapViews.valueAt(index);
			scrapViews.remove(scrapViews.keyAt(index));
			return r;
		} else {
			return null;
		}
	}
Makes sure that the size of scrapViews does not exceed the size of
activeViews. (This can happen if an adapter does not recycle its views).
library/src/main/java/com/shizhefei/view/viewpager/RecycleBin.java