/** 开始上拉加载更多，会触发delegate的onBGARefreshLayoutBeginRefreshing方法 */
public void beginLoadingMore() {
if (!mIsLoadingMore
&& mLoadMoreFooterView != null
&& mDelegate != null
&& mDelegate.onBGARefreshLayoutBeginLoadingMore(this)) {
mIsLoadingMore = true;
if (mIsShowLoadingMoreView) {
showLoadingMoreView();
}
}
}
