如何使用BootstrapValidator验证DropdownList的元素

<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/css/bootstrap.min.css">
<link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap-validator@0.11.9/dist/css/bootstrapValidator.min.css">
<script src="https://code.jquery.com/jquery-3.6.0.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/js/bootstrap.bundle.min.js"></script>
<script src="https://cdn.jsdelivr.net/npm/bootstrap-validator@0.11.9/dist/js/bootstrapValidator.min.js"></script>

<form id="myForm">
  <div class="form-group">
    <label for="dropdown">DropdownList</label>
    <select class="form-control" id="dropdown" name="dropdown">
      <option value="">请选择</option>
      <option value="option1">选项1</option>
      <option value="option2">选项2</option>
      <option value="option3">选项3</option>
    </select>
  </div>
  <button type="submit" class="btn btn-primary">提交</button>
</form>

$(document).ready(function() {
  $('#myForm').bootstrapValidator({
    fields: {
      dropdown: {
        validators: {
          notEmpty: {
            message: '请选择一个选项'
          }
        }
      }
    }
  });
});

$(document).ready(function() {
  $('#myForm').bootstrapValidator({
    // 验证规则...
  });
});

$(document).ready(function() {
  $('#myForm').bootstrapValidator({
    // 验证规则...
  }).on('success.form.bv', function(e) {
    // 阻止表单默认提交
    e.preventDefault();
    
    // 执行其他操作，如AJAX提交表单数据
    // ...
  });
});