上面的截图和你的实现就像你在谈论两件不同的事情。
您只需要一个带有CheckboxColumn的网格视图

<?php

use yii\bootstrap\ActiveForm;
use yii\grid\GridView;
use yii\helpers\Html;

$form = ActiveForm::begin([
    'action' => ['index'],
    'method' => 'get',
    'id' => 'user_form',
    'options' => ['class' => 'lfp-listing']
]);
echo Html::submitButton('Send Reminder', ['class' => 'btn is-primary', 'name' => 'action', 'value' => 'send_reminder']);

echo GridView::widget([
    'dataProvider' => $dataprovider,
    'columns' => [
        'id',
        'name',
        'email',
        [
            'class' => 'yii\grid\CheckboxColumn',
            'checkboxOptions' =>
            function ($model) {
                return ['value' => $model->id, 'class' => '', 'id' => 'checkbox'];
            }
        ],
    ]
]);
ActiveForm::end();

考虑到您的Action是actionIndex（）

public function actionIndex()
    {
        if (isset($_REQUEST['action']) && isset($_REQUEST['selection']) && 'send_reminder' == $_REQUEST['action'] ) {
            foreach ($_REQUEST['selection'] as $userIds) {
                //write down the email code here....
            }
}