function Simplest::buildForm

Overrides FormInterface::buildForm

File

modules/ajax_example/src/Form/Simplest.php, line 23

Class

Simplest

A relatively simple AJAX demonstration form.

Namespace

Code

public function buildForm(array $form, FormStateInterface $form_state) {
    $form['change_this'] = [
        '#title' => $this->t("Choose something and explain why"),
        '#type' => 'select',
        '#options' => [
            'one' => 'one',
            'two' => 'two',
            'three' => 'three',
        ],
        '#ajax' => [
            // #ajax has two required keys: callback and wrapper.
            // callback is a callable that will be called when this element changes.
'callback' => '::promptCallback',
            // wrapper is the HTML ID of the page element that will be replaced.
'wrapper' => 'replace-textfield-container',
        ],
    ];
    // The replace-textfield-container container will be replaced whenever
    // change_this is updated.
    $form['replace_textfield_container'] = [
        '#type' => 'container',
        '#attributes' => [
            'id' => 'replace-textfield-container',
        ],
    ];
    $form['replace_textfield_container']['replace_textfield'] = [
        '#type' => 'textfield',
        '#title' => $this->t("Why"),
    ];
    // An AJAX request calls the form builder function for every change.
    // We can change how we build the form based on $form_state.
    $value = $form_state->getValue('change_this');
    // The getValue() method returns NULL by default if the form element does
    // not exist. It won't exist yet if we're building it for the first time.
    if ($value !== NULL) {
        $form['replace_textfield_container']['replace_textfield']['#description'] = $this->t("Say why you chose '@value'", [
            '@value' => $value,
        ]);
    }
    return $form;
}