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NSString method constrainedToSize?

In order not to get confused with the method NSString sizeWithFontthat returns CGSize, I am looking for a method that returns NSString, limited to a specific one CGSize. The reason I want to do this is because when drawing text with, Core TextI can get the addition of ellipses (...) at the end of the line. I know that the method NSString drawInRectdoes this for me, but I use Core Text, but kCTLineBreakByTruncatingTailcut off the end of each line, not the end of the line.

There is this method that I found that cuts a string to a certain width, and it is not so difficult to change to make it work a CGSize, but the algorithm is incredibly slow for long lines and is practically not applicable. (It took more than 10 seconds to truncate a long line). There should be a more “computer science” / mathematical algorithm, a way to do it faster. Anyone bold enough to try to implement a faster implementation?

Edit: I was able to do this using a binary algorithm:

-(NSString*)getStringByTruncatingToSize:(CGSize)size string:(NSString*)string withFont:(UIFont*)font
{
    int min = 0, max = string.length, mid;
    while (min < max) {
        mid = (min+max)/2;

        NSString *currentString = [string substringWithRange:NSMakeRange(min, mid - min)];
        CGSize currentSize = [currentString sizeWithFont:font constrainedToSize:CGSizeMake(size.width, MAXFLOAT)];

        if (currentSize.height < size.height){
            min = mid + 1;
        } else if (currentSize.height > size.height) {
            max = mid - 1;
        } else {
            break;
        }
    }

   NSMutableString *finalString = [[string substringWithRange:NSMakeRange(0, min)] mutableCopy];
   if(finalString.length < self.length)
         [finalString replaceCharactersInRange:NSMakeRange(finalString.length - 3, 3) withString:@"..."];

   return finalString;
}

The problem is that it sometimes cuts the string too short when it has room for spares. I think this is what the last condition comes to. How can I make sure it doesn't cut too much?

+3
1

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THIS IS THE STRING THAT YOU WANT TO TRUNCATE
                       ^

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THIS IS THE STRING THAT YOU WANT TO TRUNCATE
          ^            |

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THIS IS THE STRING THAT YOU WANT TO TRUNCATE
                       |         ^

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int binary_search(NSString *A, float max_width, int imin, int imax)
{
  // continue searching while [imin,imax] is not empty
  while (imax >= imin)
    {
      /* calculate the midpoint for roughly equal partition */
      int imid = (imin + imax) / 2;

      // determine which subarray to search
      float width = ComputeWidthOfString([A substringToIndex:imid]);
      if      (width < max_width)
        // change min index to search upper subarray
        imin = imid + 1;
      else if (width > max_width )
        // change max index to search lower subarray
        imax = imid - 1;
      else
        // exact match found at index imid
        return imid;
  }
  // Normally, this is the "not found" case, but we're just looking for
  // the best fit, so we return something here.
  return imin;
}

, , , imin imax, .

+6

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