Symfony 3：仅在出现错误时自定义您的类输入字段

Question

Usually we can customize the attribute class of an input field from twig with

{{ form_widget(form.username,{'attr':{
       'class':'input',
       'placeholder':'Write your username'
    }}) }}

But how to add a class depending upon the fact that this field has an error?

For example I want my input tag to have an additional class "is-danger" if there is an error encountered during submission

Answer 1

I found a workaround by setting a variable before:

            {% if form_errors(form.username) is not empty %}
                    {% set class = "input is-danger" %}
                {% else %}
                    {% set class = "input" %}
                {% endif %}
                {{ form_widget(form.username,{'attr':{
                    'class':class,
                    'placeholder':'Write your username'
                }}) }}

It is a bit cumbersome to post all of that in the template though.