UIButton居中图片和文字

- (void)centerImageAndButton:(CGFloat)gap imageOnTop:(BOOL)imageOnTop {
    NSInteger sign = imageOnTop ? 1 : -1;

    CGSize imageSize = self.imageView.frame.size;
    self.titleEdgeInsets = UIEdgeInsetsMake((imageSize.height+gap)*sign, -imageSize.width, 0, 0);

    CGSize titleSize = self.titleLabel.bounds.size;
    self.imageEdgeInsets = UIEdgeInsetsMake(-(titleSize.height+gap)*sign, 0, 0, -titleSize.width);  
}