Bootstrap内联表单不适用于简单表单

Question

我无法显示我的simple_form内联：

<div class="row">
  <div class="col-md-12">
    <%= simple_form_for '', :html => { :class => 'form-inline' }, url: vehicleTrack_path, :method => :get do |f| %>
        <%= f.input :search, collection: @all_vehicles, :label_method => :objectno, :label => 'Vehiculo' %>
        <%= f.button :submit, value: "Buscar",:name => nil%>
    <% end %>
   </div>
</div>

显示器：

但是，如果我只是尝试使用Bootstrap演示代码，它可以正常工作：

<form class="form-inline">
  <input type="text" class="input-small" placeholder="Email">
  <input type="password" class="input-small" placeholder="Password">
  <label class="checkbox">
    <input type="checkbox"> Remember me
  </label>
  <button type="submit" class="btn">Sign in</button>
</form>

显示器：