Android EditText that automatically formats a UK sort code as the user types it in.

SortCodeView.java

import android.content.Context;
import android.support.v7.widget.AppCompatEditText;
import android.text.Editable;
import android.text.InputFilter;
import android.text.InputType;
import android.text.Spanned;
import android.text.TextWatcher;
import android.text.method.DigitsKeyListener;
import android.util.AttributeSet;

public class SortCodeView extends AppCompatEditText {

	{

		setHint(getContext().getString(R.string.sort_code));

		setInputType(InputType.TYPE_CLASS_NUMBER);

		setKeyListener(DigitsKeyListener.getInstance("0123456789-"));

		// this filter filters for characters that will destroy the pattern and either
		// accepts them or rejects them
		setFilters(new InputFilter[]{
			new InputFilter() {
				@Override
				public CharSequence filter(CharSequence source, int start, int end,
					Spanned destination, int destinationStart, int destinationEnd) {
					CharSequence result = null;
					if (end > start) {
						// adding
						String destinationString = destination.toString();
						String resultingTxt = destinationString.substring(0, destinationStart) +
							source.subSequence(start, end) +
							destinationString.substring(destinationEnd);
						if (!resultingTxt.matches("^(\\d{1,2})(-\\d{0,2}|-\\d{2}-\\d{0,2})?$")) {
							result = "";
						}
					}
					// return null to accept the input or empty to reject it
					return result;
				}
			}});

		addTextChangedListener(new TextWatcher() {
			boolean mAdding = false;
			boolean mRemovedDash = false;

			@Override
			public void beforeTextChanged(CharSequence s, int start, int count, int after) {
				if (count > after && s.length() > 0 && s.charAt(start) == '-') {
					mRemovedDash = true;
				}
			}

			@Override
			public void onTextChanged(CharSequence s, int start, int before, int count) {
				mAdding = count > before;
			}

			@Override
			public void afterTextChanged(Editable s) {
				if (mAdding) {
					// let's add a separator every two characters automatically
					String text = s.toString();
					String[] pieces = text.split("\\-");
					String lastPiece = pieces[pieces.length - 1];
					if (lastPiece.length() == 2 && s.charAt(s.length() - 1) != '-') {
						s.append('-');
					}
				} else if (mRemovedDash) {
					removeTextChangedListener(this);
					// remove the next number automatically after a dash is removed
					s.delete(s.length() - 1, s.length());
					mRemovedDash = false;
					addTextChangedListener(this);
				}
			}
		});

	}

	public SortCodeView(Context context) {
		super(context);
	}

	public SortCodeView(Context context, AttributeSet attrs) {
		super(context, attrs);
	}

	public SortCodeView(Context context, AttributeSet attrs, int defStyleAttr) {
		super(context, attrs, defStyleAttr);
	}

}