cell的高度动态计算问题

菜鸟一个，谢谢指教。

    NSMutableAttributedString * attributedString1 = [[NSMutableAttributedString alloc] initWithString:item.content];
    NSMutableParagraphStyle * paragraphStyle1 = [[NSMutableParagraphStyle alloc] init];
    [paragraphStyle1 setLineSpacing:24];
    [attributedString1 addAttribute:NSParagraphStyleAttributeName value:paragraphStyle1 range:NSMakeRange(0, [item.content length])];
    [label setAttributedText:attributedString1];
    CGSize boundSize = CGSizeMake(IPHONE_WIDTH-32, CGFLOAT_MAX);
    NSDictionary *attribute = @{NSFontAttributeName: [UIFont systemFontOfSize:12], NSParagraphStyleAttributeName : paragraphStyle1};
    CGSize size = [item.content boundingRectWithSize:boundSize options: NSStringDrawingTruncatesLastVisibleLine | NSStringDrawingUsesLineFragmentOrigin | NSStringDrawingUsesFontLeading attributes:attribute context:nil].size;
    return size.height;

这是代码

根据这个方法来实现

- (CGRect)boundingRectWithSize:(CGSize)size options:(NSStringDrawingOptions)options attributes:(nullable NSDictionary *)attributes context:(nullable NSStringDrawingContext *)context NS_AVAILABLE(10_11, 7_0);

解释一下：
第一个参数size:这个是一个CGSize格式的，宽度是cell的宽 或者你定义的任何控件或者什么东西。。。高度取CGFLOAT_MAX表示无限大
第二个参数options是一个(NSStringDrawingOptions)类型的，是一个枚举值

typedef NS_OPTIONS(NSInteger, NSStringDrawingOptions) {
    NSStringDrawingUsesLineFragmentOrigin = 1 << 0, // The specified origin is the line fragment origin, not the base line origin
    NSStringDrawingUsesFontLeading = 1 << 1, // Uses the font leading for calculating line heights
    NSStringDrawingUsesDeviceMetrics = 1 << 3, // Uses image glyph bounds instead of typographic bounds
    NSStringDrawingTruncatesLastVisibleLine NS_ENUM_AVAILABLE(10_5, 6_0) = 1 << 5, // Truncates and adds the ellipsis character to the last visible line if the text doesn't fit into the bounds specified. Ignored if NSStringDrawingUsesLineFragmentOrigin is not also set.

} NS_ENUM_AVAILABLE(10_0, 6_0);

NSStringDrawingUsesLineFragmentOrigin：

The specified origin is the line fragment origin, not the base line origin
指定的orgin是line frgment orgin,不是base line origin.英文不好。。

NSStringDrawingUsesFontLeading：

使用字体间的行距来计算。行距=字体大小+间距

NSStringDrawingUsesDeviceMetrics：

我理解的就是计算的时候加上特殊字符比如/r/n/t这些东西

NSStringDrawingTruncatesLastVisibleLine：

[如果文本内容超出指定的矩形限制，文本将被截去并在最后一个字符后加上省略号。如果没有指定NSStringDrawingUsesLineFragmentOrigin选项，则该选项被忽略。]

attributes参数传入的是一个字典：参数格式如下
NSDictionary *

   NSMutableAttributedString * attributedString1 = [[NSMutableAttributedString alloc] initWithString:item.content];
    NSMutableParagraphStyle * paragraphStyle1 = [[NSMutableParagraphStyle alloc] init];
    [paragraphStyle1 setLineSpacing:24];
    [attributedString1 addAttribute:NSParagraphStyleAttributeName value:paragraphStyle1 range:NSMakeRange(0, [item.content length])];

这是创建了一个attributedString1的NSMutableAttributedString对象

NSMutableParagraphStyle * paragraphStyle1 = [[NSMutableParagraphStyle alloc] init];

创建一个装饰字体的对象 给他设置行间距

[paragraphStyle1 setLineSpacing:24];

[attributedString addAttribute:NSParagraphStyleAttributeName value:paragraphStyle range:NSMakeRange(0, [item.content length])];

设置添加的字体长度

今天我碰到的问题 上面那些都写了以后
要设置下面这句，网上大部分写的都是

NSDictionary *attribute = @{NSFontAttributeName: [UIFont systemFontOfSize:12]};

这一句加上了设置的paragraphStyle，这样最后得到的CGSize是所有字体按照目标的size算出来的，我需要拿到这个高度。。。。

 NSDictionary *attribute = @{NSFontAttributeName: [UIFont systemFontOfSize:12], NSParagraphStyleAttributeName : paragraphStyle};

文笔不好。。。写了半天。。。。