UITextView的NSKernAttributeName始终为0

Question

我在iOS 6上的UITextView的attributedText属性上，在特定范围内，将NSKernAttributeName设置为不同的浮点值。每次使用attributedText的enumerateAttribute选项块方法检索值时，Kerning都设置为0。代码如下。

检索

        NSAttributedString *currentText = _textView.attributedText;
        [currentText enumerateAttribute:NSKernAttributeName inRange:NSMakeRange(0, currentText.length) options:NSAttributedStringEnumerationLongestEffectiveRangeNotRequired usingBlock:^(id value, NSRange range, BOOL *stop){
              float value = [(NSNumber *)value floatValue];
              //Do something with value, but logs show value is always 0 
        }];

存储

      NSMutableAttributedString *updatedText = self.textView.attributedText.mutableCopy; 
     _kernValue += 0.1f;
     NSDictionary *attributes = @{
                                 NSForegroundColorAttributeName: UIColor.linkColor,
                                 NSFontAttributeName: [UIFont systemFontOfSize:14.0],
                                 NSKernAttributeName: [NSNumber numberWithFloat:_kernValue]
                                 };
     NSMutableAttributedString *replacementString = [[NSMutableAttributedString alloc] initWithString:[NSString stringWithFormat:@"%@ ", myString] attributes:attributes];
     [updatedText replaceCharactersInRange:myRange withAttributedString:replacementString];
    self.textView.attributedText = updatedText;

Answer 1

来自NSAttributedString标头：

UIKIT_EXTERN NSString *const NSKernAttributeName NS_AVAILABLE_IOS(6_0);                //

NSNumber包含浮点值，以点为单位；修改默认紧排的数量。0表示紧排已禁用。（注意：iOS不支持nil和0以外的值）