private Dictionary<char, int> DoFindControlChars(NSString str) { var chars = new Dictionary<char, int>(); int len = (int) str.length(); NSRange range = new NSRange(0, len); while (true) { NSRange temp = str.rangeOfCharacterFromSet_options_range( NSCharacterSet.controlCharacterSet(), Enums.NSLiteralSearch, range); if (temp.length == 0) break; char ch = str.characterAtIndex((uint) temp.location); if (ch != '\r' && ch != '\n' && ch != '\t' && ch != Constants.BOM[0]) { if (chars.ContainsKey(ch)) chars[ch] = chars[ch] + 1; else chars[ch] = 1; } range = new NSRange(temp.location + 1, len - (temp.location + 1)); } return chars; }