Format credit card in edit text in android

Question

How to make EditText accept input in format:

4digit 4digit 4digit 4digit 

I tried Custom format edit text input android to acc

Answer 1

This is my implementation base on Igor Tyulkanov's idea, it has a small improvement that fix the cursor position problem

class CardNumbersInputWatcher(private val editText: EditText) : TextWatcher {
  companion object {
    private const val TOTAL_SYMBOLS = 19
    private const val DIVIDER_DISTANCE = 4
    private const val DIVIDER = ' '
  }

  override fun afterTextChanged(s: Editable) {
    if (!isInputCorrect(s, TOTAL_SYMBOLS, DIVIDER_DISTANCE, DIVIDER)) {
      val beforeCurPos = editText.selectionStart
      val beforeLength = s.length
      s.replace(0, s.length, buildCorrectString(s, TOTAL_SYMBOLS, DIVIDER_DISTANCE, DIVIDER))
      if (beforeLength > TOTAL_SYMBOLS && beforeCurPos <= s.length && editText.selectionStart < beforeCurPos) {
        editText.setSelection(beforeCurPos)
      }
    }
  }

  override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) = Unit
  override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) = Unit
}

private fun isInputCorrect(s: Editable, totalSymbols: Int, dividerDistance: Int, divider: Char): Boolean {
  if (s.length > totalSymbols) {
    return false
  }
  return s.withIndex().all { (index, c) ->
    if (index != 0 && ((index + 1) % (dividerDistance + 1) == 0)) {
      // it should be divider
      c == divider
    } else {
      c.isDigit()
    }
  }
}

private fun buildCorrectString(s: Editable, totalSymbols: Int, dividerDistance: Int, divider: Char): String {
  return buildString {
    for (c in s) {
      if (length >= totalSymbols) break
      if (!c.isDigit()) continue
      if (length > 0 && ((length + 1) % (dividerDistance + 1)) == 0) append(divider)
      append(c)
    }
  }
}