iOS中根据字体大小计算文本内容高度

方法如下，调用即可：

- (CGSize)sizeWithFont:(UIFont *)font width:(CGFloat)width content:(NSString *)content {

    NSDictionary *attrs = @{NSFontAttributeName : font};
    CGSize size = CGSizeMake(width, CGFLOAT_MAX);
    return [content boundingRectWithSize:size 
    options:NSStringDrawingUsesLineFragmentOrigin attributes:attrs context:nil].size;
}