Android SDK怎么从AVObject中获取AVFile的List啊

public void addImage(AVFile img) {
	addUnique("images", img);
}

public void setImages(List<AVFile> imgs) {
	addAll("images", imgs);
}

public List getImages() {
	return getList("images");
}

getImages获取到的是AVObject的List，没法转成AVFile；用AVFile.withAVObject也不行，求助啊