colorFromHex function

Color? colorFromHex(String inputString, { bool enableAlpha = true, })

Try to convert text input or any String to valid Color. The String must be provided in one of those formats:

• RGB
• #RGB
• RRGGBB
• #RRGGBB
• AARRGGBB
• #AARRGGBB

Where: A stands for Alpha, R for Red, G for Green, and B for blue color. It will only accept 3/6/8 long HEXs with an optional hash (#) at the beginning. Allowed characters are Latin A-F case insensitive and numbers 0-9. Optional enableAlpha can be provided (it's true by default). If it's set to false transparency information (alpha channel) will be removed.

/// // Valid 3 digit HEXs:
colorFromHex('abc') == Color(0xffaabbcc)
colorFromHex('ABc') == Color(0xffaabbcc)
colorFromHex('ABC') == Color(0xffaabbcc)
colorFromHex('#Abc') == Color(0xffaabbcc)
colorFromHex('#abc') == Color(0xffaabbcc)
colorFromHex('#ABC') == Color(0xffaabbcc)
// Valid 6 digit HEXs:
colorFromHex('aabbcc') == Color(0xffaabbcc)
colorFromHex('AABbcc') == Color(0xffaabbcc)
colorFromHex('AABBCC') == Color(0xffaabbcc)
colorFromHex('#AABbcc') == Color(0xffaabbcc)
colorFromHex('#aabbcc') == Color(0xffaabbcc)
colorFromHex('#AABBCC') == Color(0xffaabbcc)
// Valid 8 digit HEXs:
colorFromHex('ffaabbcc') == Color(0xffaabbcc)
colorFromHex('ffAABbcc') == Color(0xffaabbcc)
colorFromHex('ffAABBCC') == Color(0xffaabbcc)
colorFromHex('ffaabbcc', enableAlpha: true) == Color(0xffaabbcc)
colorFromHex('FFAAbbcc', enableAlpha: true) == Color(0xffaabbcc)
colorFromHex('ffAABBCC', enableAlpha: true) == Color(0xffaabbcc)
colorFromHex('FFaabbcc', enableAlpha: true) == Color(0xffaabbcc)
colorFromHex('#ffaabbcc') == Color(0xffaabbcc)
colorFromHex('#ffAABbcc') == Color(0xffaabbcc)
colorFromHex('#FFAABBCC') == Color(0xffaabbcc)
colorFromHex('#ffaabbcc', enableAlpha: true) == Color(0xffaabbcc)
colorFromHex('#FFAAbbcc', enableAlpha: true) == Color(0xffaabbcc)
colorFromHex('#ffAABBCC', enableAlpha: true) == Color(0xffaabbcc)
colorFromHex('#FFaabbcc', enableAlpha: true) == Color(0xffaabbcc)
// Invalid HEXs:
colorFromHex('bc') == null // length 2
colorFromHex('aabbc') == null // length 5
colorFromHex('#ffaabbccd') == null // length 9 (+#)
colorFromHex('aabbcx') == null // x character
colorFromHex('#aabbвв') == null // в non-latin character
colorFromHex('') == null // empty

Reference: https://en.wikipedia.org/wiki/Web_colors#Hex_triplet

Implementation

Color? colorFromHex(String inputString, {bool enableAlpha = true}) {
  // Registers validator for exactly 6 or 8 digits long HEX (with optional #).
  final RegExp hexValidator = RegExp(kCompleteValidHexPattern);
  // Validating input, if it does not match — it's not proper HEX.
  if (!hexValidator.hasMatch(inputString)) return null;
  // Remove optional hash if exists and convert HEX to UPPER CASE.
  String hexToParse = inputString.replaceFirst('#', '').toUpperCase();
  // It may allow HEXs with transparency information even if alpha is disabled,
  if (!enableAlpha && hexToParse.length == 8) {
    // but it will replace this info with 100% non-transparent value (FF).
    hexToParse = 'FF${hexToParse.substring(2)}';
  }
  // HEX may be provided in 3-digits format, let's just duplicate each letter.
  if (hexToParse.length == 3) {
    hexToParse = hexToParse.split('').expand((i) => [i * 2]).join();
  }
  // We will need 8 digits to parse the color, let's add missing digits.
  if (hexToParse.length == 6) hexToParse = 'FF$hexToParse';
  // HEX must be valid now, but as a precaution, it will just "try" to parse it.
  final intColorValue = int.tryParse(hexToParse, radix: 16);
  // If for some reason HEX is not valid — abort the operation, return nothing.
  if (intColorValue == null) return null;
  // Register output color for the last step.
  final color = Color(intColorValue);
  // Decide to return color with transparency information or not.
  return enableAlpha ? color : color.withAlpha(255);
}