android format edittext to display spaces after every 4 characters

Question

Android - I want to get a number input from the user into an EditText - it needs to be separated by spaces - every 4 characters. Example: 123456781234 -> 1234 5678 1234

Answer 1

I have created a class that encapsulates the given behavior.

/**
 * Custom [TextWatcher] class that appends a given [separator] for every [interval].
 */
abstract class SeparatorTextWatcher(
    private val separator: Char,
    private val interval: Int
) : TextWatcher {

    private var dirty = false
    private var isDelete = false

    override fun afterTextChanged(editable: Editable?) {
        if (dirty) return

        dirty = true
        val text = editable.toString().handleSeparator()
        onAfterTextChanged(text)
        dirty = false
    }

    override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
        // Empty
    }

    override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
        isDelete = before != 0
    }

    private fun String.handleSeparator(): String {
        val stringBuilder = StringBuilder(this)

        if (length > 0 && length.rem(interval + 1) == 0) {
            if (isDelete) {
                stringBuilder.deleteCharAt(length - 1)
            } else {
                stringBuilder.insert(length - 1, separator)
            }
        }

        return stringBuilder.toString()
    }

    /**
     * Subclasses must implement this method to get the formatted text.
     */
    abstract fun onAfterTextChanged(text: String)
}

Here's a snippet on how to use it:

editText.addTextChangedListener(object : SeparatorTextWatcher(' ', 4) {
            override fun onAfterTextChanged(text: String) {
                editText.run {
                    setText(text)
                    setSelection(text.length)
                }
            }
        })