Wrapper for TextWatcher

TextWatcherListener.kt

open class TextWatcherListener(
    private val editText: EditText,
    private val listener: EditText.(String, String, String, String) -> Unit
) : TextWatcher {

    private var before: String = ""
    private var old: String = ""
    private var new: String = ""
    private var after: String = ""
    private var isIgnore = false

    override fun beforeTextChanged(sequence: CharSequence, start: Int, count: Int, after: Int) {
        this.before = sequence.subSequence(0, start).toString()
        this.old = sequence.subSequence(start, start + count).toString()
        this.after = sequence.subSequence(start + count, sequence.length).toString()
    }

    override fun onTextChanged(sequence: CharSequence, start: Int, before: Int, count: Int) {
        this.new = sequence.subSequence(start, start + count).toString()
    }

    override fun afterTextChanged(sequence: Editable) {
        if (isIgnore) {
            return
        }
        isIgnore = true
        listener(editText, before, old, new, after)
        isIgnore = false
    }

    companion object {
        fun EditText.addTextChangedListener(listener: EditText.(String, String, String, String) -> Unit) {
            addTextChangedListener(TextWatcherListener(this, listener))
        }
    }
}

Usage.kt

editText.addTextChangedListener { before, old, new, after ->
    //this <- given EditText
    //safe update EditText
    val oldString = before + old + after
    val newString = before + new + after
}