iOS获取Label高度的几种方法与对比

// return 'best' size to fit given size. does not actually resize view. Default is return existing view size
- (CGSize)sizeThatFits:(CGSize)size;

UILabel *testLabel = [[UILabel alloc] init];
testLabel.font = [UIFont systemFontOfSize:30];
testLabel.text = @"Today is a fine day";
CGSize size = [testLabel sizeThatFits:CGSizeMake(200, 30)];
NSLog(@"size = %@", NSStringFromCGSize(size));

// calls sizeThatFits: with current view bounds and changes bounds size.
- (void)sizeToFit;

UILabel *testLabel = [[UILabel alloc] init];
testLabel.font = [UIFont systemFontOfSize:30];
testLabel.text = @"Today is a fine day";
[testLabel sizeToFit];
NSLog(@"size = %@", NSStringFromCGSize(testLabel.frame.size));

- (CGSize)sizeWithAttributes:(nullable NSDictionary<NSString *, id> *)attrs NS_AVAILABLE(10_0, 7_0);

NSString *text = @"Today is a fine day";
UIFont *font = [UIFont systemFontOfSize:30];
CGSize size = [text sizeWithAttributes:@{
           NSFontAttributeName : font
           }];
NSLog(@"size = %@", NSStringFromCGSize(size));

// NOTE: All of the following methods will default to drawing on a baseline, limiting drawing to a single line.
// To correctly draw and size multi-line text, pass NSStringDrawingUsesLineFragmentOrigin in the options parameter.
- (CGRect)boundingRectWithSize:(CGSize)size options:(NSStringDrawingOptions)options attributes:(nullable NSDictionary<NSString *, id> *)attributes context:(nullable NSStringDrawingContext *)context NS_AVAILABLE(10_11, 7_0);

typedef NS_OPTIONS(NSInteger, NSStringDrawingOptions) {
 // The specified origin is the line fragment origin, not the base line origin
 // 整个文本将以每行组成的矩形为单位计算整个文本的尺寸
 NSStringDrawingUsesLineFragmentOrigin = 1 << 0, 

 // Uses the font leading for calculating line heights
 // 使用字体的行间距来计算文本占用的范围，即每一行的底部到下一行的底部的距离计算
 NSStringDrawingUsesFontLeading = 1 << 1, 

 // Uses image glyph bounds instead of typographic bounds
 // 将文字以图像符号计算文本占用范围，而不是排版的边界
 NSStringDrawingUsesDeviceMetrics = 1 << 3,

 // 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.
 // 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 NSStringDrawingUsesLineFragmentOrigin 没有设置，则该选项不生效
 NSStringDrawingTruncatesLastVisibleLine NS_ENUM_AVAILABLE(10_5, 6_0) = 1 << 5, 
} NS_ENUM_AVAILABLE(10_0, 6_0);

NSString *text = @"Today is a fine day";
UIFont *font = [UIFont systemFontOfSize:30];
CGRect suggestedRect = [text boundingRectWithSize:CGSizeMake(800, MAXFLOAT)
            options:NSStringDrawingUsesFontLeading
           attributes:@{ NSFontAttributeName : font }
            context:nil];
NSLog(@"size = %@", NSStringFromCGSize(suggestedRect.size));