button中可能要用到的（留给本身的笔记）

_voteAgainstButton = [[XWVoteButton alloc] initWithFrame:CGRectMake(85, y, 65, 46)];
    UIImage *nAImage = [UIImage imageNamed:@"icon_against_enable.png"];
    UIImage *sAImage = [UIImage imageNamed:@"icon_against_active.png"];
    [_voteAgainstButton setFaceButtonImage:nAImage andSelectedImage:sAImage];

button中设置初始按钮和选中的按钮