public class UserNameStep extends Step<String> {

    private EditText userNameView;

    public UserNameStep(String stepTitle) {
        super(stepTitle);
    }

    @Override
    protected View createStepContentLayout() {
        // Here we generate the view that will be used by the library as the content of the step.
        // In this case we do it programmatically, but we could also do it by inflating an XML layout.
        userNameView = new EditText(getContext());
        userNameView.setSingleLine(true);
        userNameView.setHint("Your Name");
        ...
        userNameView.addTextChangedListener(new TextWatcher() {
            ...
            @Override
            public void onTextChanged(CharSequence s, int start, int before, int count) {
                // Whenever the user updates the user name text, we update the state of the step.
                // The step will be marked as completed only if its data is valid, which will be
                // checked automatically by the form with a call to isStepDataValid().
                markAsCompletedOrUncompleted(true);
            }
        });

        return userNameView;
    }
    
    @Override
    protected IsDataValid isStepDataValid(String stepData) {
        // The step's data (i.e., the user name) will be considered valid only if it is longer than 
        // three characters. In case it is not, we will display an error message for feedback.
        // In an optional step, you should implement this method to always return a valid value.
        boolean isNameValid = stepData.length() >= 3;
        String errorMessage = !isNameValid ? "3 characters minimum" : "";

        return new IsDataValid(isNameValid, errorMessage);
    }

    @Override
    public String getStepData() {
        // We get the step's data from the value that the user has typed in the EditText view.
        Editable userName = userNameView.getText();
        return userName != null ? userName.toString() : "";
    }

    @Override
    public String getStepDataAsHumanReadableString() {
        // Because the step's data is already a human-readable string, we don't need to convert it.
        // However, we return "(Empty)" if the text is empty to avoid not having any text to display.
        // This string will be displayed in the subtitle of the step whenever the step gets closed.
        String userName = getStepData();        
        return !userName.isEmpty() ? userName : "(Empty)";
    }

    @Override
    protected void onStepOpened(boolean animated) {
        // This will be called automatically whenever the step gets opened.
    }

    @Override
    protected void onStepClosed(boolean animated) {
        // This will be called automatically whenever the step gets closed.
    }
    
    @Override
    protected void onStepMarkedAsCompleted(boolean animated) {
        // This will be called automatically whenever the step is marked as completed.
    }

    @Override
    protected void onStepMarkedAsUncompleted(boolean animated) {
        // This will be called automatically whenever the step is marked as uncompleted.
    }

    @Override
    protected void restoreStepData(String stepData) {
        // To restore the step after a configuration change, we restore the text of its EditText view.
        userNameView.setText(stepData);
    }
}

public class CreateUserAccountActivity extends Activity implements StepperFormListener {

    private UserNameStep userNameStep;
    private UserEmailStep userEmailStep;
    private UserAgeStep userAgeStep;
    
    private VerticalStepperFormView verticalStepperForm;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.new_user_form_activity);

        // Create the steps.
        userNameStep = new UserNameStep("User Name");
        userEmailStep = new UserEmailStep("User Email");
        userAgeStep = new UserAgeStep("User Age");

        // Find the form view, set it up and initialize it.
        verticalStepperForm = findViewById(R.id.stepper_form);
        verticalStepperForm
            .setup(this, userNameStep, userEmailStep, userAgeStep)
            .init();
    }

    @Override
    public void onCompletedForm() {
        // This method will be called when the user clicks on the last confirmation button of the 
        // form in an attempt to save or send the data.
    }

    @Override
    public void onCancelledForm() {
        // This method will be called when the user clicks on the cancel button of the form.
    }

    @Override
    public void onStepAdded(int index, Step<?> addedStep) {
        // This will be called when a step is added dynamically through the form method addStep().
    }

    @Override
    public void onStepRemoved(int index) {
        // This will be called when a step is removed dynamically through the form method removeStep().
    }
}

verticalStepperForm
    .setup(this, userNameStep, userEmailStep, userAgeStep)
    .allowNonLinearNavigation(true)
    .displayBottomNavigation(false)
    .lastStepNextButtonText("Create User")
    ...
    .init();