SpoilerText-FormatText.kt

private fun updateTextView(plainText: String, ranges: MutableList<Pair<Int, Int>>) {
    val spannableString = SpannableString(plainText)

    ranges.forEach { range ->
        // Make the range
        spannableString.setSpan(object : ClickableSpan() {
            override fun onClick(widget: View) {
                // Remove clicked range from the list
                ranges.remove(Pair(range.first, range.second))

                updateTextView(plainText, ranges)
            }
        }, range.first, range.second, Spanned.SPAN_EXCLUSIVE_EXCLUSIVE)

        // Set the background to black to give it the hidden effect
        spannableString.setSpan(
            BackgroundColorSpan(Color.BLACK),
            range.first,
            range.second,
            Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
        )

        // The foreground color (text color) should match the background
        spannableString.setSpan(
            ForegroundColorSpan(Color.BLACK),
            range.first,
            range.second,
            Spanned.SPAN_EXCLUSIVE_EXCLUSIVE
        )
    }

    textView.text = spannableString
}