AutoValidatedTextInputEditText.java

public class AutoValidatedTextInputEditText extends TextInputEditText implements AutoValidatedUserInputComponent, TextViewHelper {

    List<TextValidator> validatorList = new ArrayList<>();
    boolean isValid = false;

    public AutoValidatedTextInputEditText(Context context) {
        super(context);
        SimpleCallback callback = payload -> validate();
        setOnFocusChangeListener(new OnFocusChangeListener(callback));
        addTextChangedListener(new OnTextChangeListener(callback));
    }

    public AutoValidatedTextInputEditText(Context context, TextValidator... validators) {
        super(context);
        SimpleCallback callback = payload -> validate();
        setOnFocusChangeListener(new OnFocusChangeListener(callback));
        addTextChangedListener(new OnTextChangeListener(callback));

        addValidators(validators);
    }

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

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

    /* Could not use streams to ensure backwards compatibility */
    private void validate() {
        String input = getTextAsString(this);
        for (TextValidator validator : validatorList) {
            String output = validator.validate(input);
            if (output != null) {
                setError(output);
                isValid = false;
                return;
            }
        }
        isValid = true;
    }

    public void addValidators(TextValidator... validators) {
        for (TextValidator validator : validators) {
            validatorList.add(validator);
        }
    }

    /* Implement the AutoValidatedUserInputComponent interface. 
       requestFocus() is already implemented on the View */
    public boolean hasValidInput() {
        validate();
        return isValid;
    }

    /* Simple View.OnFocusChangeListener that calls the provided callback whenever focus is lost */
    private class OnFocusChangeListener implements View.OnFocusChangeListener {
        SimpleCallback<Void> focusLostCallback;

        public OnFocusChangeListener(SimpleCallback<Void> focusLostCallback) {
            this.focusLostCallback = focusLostCallback;
        }

        @Override
        public void onFocusChange(View v, boolean hasFocus) {
            if (!v.hasFocus()) {
                focusLostCallback.call(null);
            }
        }
    }

    /* Simple TextWatcher that calls the provided callback whenever the text is changed. */
    private class OnTextChangeListener implements TextWatcher {
        SimpleCallback<Void> textChangedCallback;

        public OnTextChangeListener(SimpleCallback<Void> textChangedCallback) {
            this.textChangedCallback = textChangedCallback;
        }

        @Override
        public void beforeTextChanged(CharSequence s, int start, int count, int after) {}
        @Override
        public void onTextChanged(CharSequence s, int start, int before, int count) {
            textChangedCallback.call(null);
        }
        @Override
        public void afterTextChanged(Editable s){}
    }
}