Masonry.h

[_dropView mas_makeConstraints:^(MASConstraintMaker *make) {
            make.top.equalTo(rightBgView.mas_top);
            make.left.equalTo(rightBgView.mas_left);
            make.right.equalTo(rightBgView.mas_right);
            make.bottom.equalTo(rightBgView.mas_bottom);
}];