Vaadin:如何将validation false设置为来自侦听器的表单

FormLayout formLayout = new FormLayout();
TextField usernameField = new TextField("Username");
TextField passwordField = new TextField("Password");

Binder<DataObject> binder = new Binder<>(DataObject.class);
binder.forField(usernameField)
    .asRequired("Username is required")
    .bind(DataObject::getUsername, DataObject::setUsername);
binder.forField(passwordField)
    .asRequired("Password is required")
    .bind(DataObject::getPassword, DataObject::setPassword);

formLayout.add(usernameField, passwordField);

Button submitButton = new Button("Submit");
submitButton.addClickListener(event -> {
    if (binder.validate().isOk()) {
        // 执行表单提交操作
    } else {
        // 当 validation 失败时，可以在这里设置相应的逻辑
    }
});