Validatable Edit Text

ValidatableEditText.java

import android.content.Context;
import android.support.annotation.Nullable;
import android.text.Editable;
import android.text.TextWatcher;
import android.util.AttributeSet;
import android.util.Log;

import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;

public class ValidatableEditText extends android.support.v7.widget.AppCompatEditText {

	public static final String TAG = ValidatableEditText.class.getSimpleName();

	public interface OnValidateListener {
		void onValidated(boolean isValid, String input);
	}

	private static final String REGEX_NON_EMPTY = ".*\\S.*";

	private @Nullable OnValidateListener onValidateListener;
	private boolean isValid;
	private Pattern validationPattern;

	public ValidatableEditText(Context context, AttributeSet attrs, int defStyle) {
		super(context, attrs, defStyle);
		init();
	}

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

	private void init() {
		setValidationRegex(REGEX_NON_EMPTY);
		addTextChangedListener(new TextWatcher() {
			@Override
			public void beforeTextChanged(CharSequence s, int start, int count, int after) {
				//ignore
			}

			@Override
			public void onTextChanged(CharSequence s, int start, int before, int count) {
				//ignore
			}

			@Override
			public void afterTextChanged(Editable s) {
				revalidate(validationPattern.matcher(s).matches());
			}
		});
	}

	private void revalidate(boolean isValid) {
		if (this.isValid != isValid) {
			this.isValid = isValid;
			if (onValidateListener != null) {
				onValidateListener.onValidated(isValid, getText().toString());
			}
		}
	}

	public void setOnValidateListener(OnValidateListener onValidateListener) {
		this.onValidateListener = onValidateListener;
	}

	public void setValidationRegex(String validationRegex) {
		try {
			validationPattern = Pattern.compile(validationRegex);
			revalidate(validationPattern.matcher(getText()).matches());
		} catch (PatternSyntaxException e) {
			Log.e(TAG, e.getMessage());
		}
	}
}

Usage:

emailEditText.setOnValidateListener(new ValidatableEditText.OnValidateListener() {
	@Override
	public void onValidated(boolean isValid, String input) {
		continueButton.setEnabled(isValid);
	}
});
emailEditText.setValidationRegex("^\\s*?(.+)@(.+?)\\s*$"); //email validation regex