private void pruneScrapViews() {
		final int maxViews = activeViews.length;
		final int viewTypeCount = this.viewTypeCount;
		final SparseArray<View>[] scrapViews = this.scrapViews;
		for (int i = 0; i < viewTypeCount; ++i) {
			final SparseArray<View> scrapPile = scrapViews[i];
			int size = scrapPile.size();
			final int extras = size - maxViews;
			size--;
			for (int j = 0; j < extras; j++) {
				scrapPile.remove(scrapPile.keyAt(size--));
			}
		}
	}
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