动态计算我文本的CGSize

// 计算文本的size
-(CGSize)sizeWithText:(NSString *)text maxSize:(CGSize)maxSize fontSize:(CGFloat)fontSize
{
    CGSize textSize = [text boundingRectWithSize:maxSize options:NSStringDrawingUsesLineFragmentOrigin attributes:@{NSFontAttributeName:[UIFont systemFontOfSize:fontSize]} context:nil].size;
    
    return textSize;
}