title: NSMutableAttributedString strike-through with animation
body: <pre><code>- (void)setStrokeLabel:(BOOL)strokeLabel
  {
      _strokeLabel = strokeLabel;
  
      if (_strokeLabel) {
          _timer = [NSTimer scheduledTimerWithTimeInterval:0.4 target:self selector:@selector(setStrokeThrough) userInfo:nil repeats:NO];
      } else {
          [self cancelStrokeThrough];
      }
  }
  
  - (void)setStrokeThrough
  {
      NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:self.attributedText];
  
      for (NSUInteger i = 1; i &lt;= [attributedString length]; i++) {
          [attributedString addAttribute:NSStrikethroughStyleAttributeName
                                   value:[NSNumber numberWithInt:1]
                                   range:NSMakeRange(0, i)];
          self.attributedText = attributedString;
      }
  }
  
  - (void)cancelStrokeThrough
  {
      NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] initWithAttributedString:self.attributedText];
      [attributedString removeAttribute:NSStrikethroughStyleAttributeName
                                  range:NSMakeRange(0, [attributedString length])];
      self.attributedText = attributedString;
  
  }
  </code></pre>
  
  <p>I want to animate <code>strike-through</code>, like todo done animation.
  As I set timer for it, the timer only handle how to show the stoke through letter by letter?? </p>