提交按钮在禁用ng后不会消失

我已经建立了一个集成了Angular的表单。在这个表单中，我希望最后的提交按钮只在表单有效时显示。有许多字段，但唯一必需的字段是用户的名称、电子邮件地址和复选框。当必需的字段无效时，表单会识别出来，但是我无法让提交按钮消失(然后重新出现)。

以下代码供参考:

index . html:

<form name="captions" ng-controller="CaptionCtrl>
    <div class="current-page">
      <div class="pages">
        <div class="page active" id="page1">
          <img src="images/blank_image.jpg">
          <div class="page-form">
            <span>&#8220;</span>
            <input type="text" ng-model="user.caption1" size="130"
                           placeholder="Enter your caption here.">
            <span>&#8221;</span>
            <br>
            <button class="page-form-submit" ng-click="pageShift(2)">NEXT</button>              </div>
        </div>
        <div class="page" id="page2">
          <img src="images/blank_image.jpg">
          <div class="page-form">
            <span>&#8220;</span>
            <input type="text" ng-model="user.caption2" size="130"
                           placeholder="Enter your caption here.">
            <span>&#8221;</span>
            <br>
            <button class="page-form-submit" ng-click="pageShift(3)">NEXT</button>
          </div>
        </div>
        <div class="page" id="page3">
          <img src="images/blank_image.jpg">
          <div class="page-form">
            <span>&#8220;</span>
            <input type="text" ng-model="user.caption3" size="130"
                           placeholder="Enter your caption here.">
            <span>&#8221;</span>
            <br>
            <button class="page-form-submit" ng-click="pageShift(4)">NEXT</button>
          </div>
        </div>
        <div class="page" id="page4">
          <img src="images/blank_image.jpg">
          <div class="page-form-submit-page">
            <h4>TO ENTER YOUR CAPTION IN THE CONTEST, TELL US YOUR NAME AND CONTACT METHOD.</h4>
            <input type="text" ng-model="user.name" size="70" placeholder="Name" required>
            <input type="email" ng-model="user.email" size="70" placeholder="E-mail Address" required>
            <br>
            <input type="checkbox" required>I have read and accept the Terms & Conditions
            <br>
            <input class="page-form-submit-page-submit" ng-disabled="captions | validateFields" ng-click="captionSubmit(user)" type="submit" value="SUBMIT">
          </div>
        </div>
        <div class="page" id="page5">
          <img src="images/blank_image.jpg">
          <div class="page-form-thankyou">
            <span><strong>THANK YOU</strong></span>
          </div>
          <div class="chapter-two-story-link"><span class="yellow">CLICK TO TELL US YOUR STORY</span></div>
        </div>
      </div>
    </div>
  </form>

如果你注意到底部，我有一个ng禁用设置"captions | validateFields"。我也试过用一个简单的真理陈述，所以这不是我设置的过滤器。

编辑:有了反馈，我已经得到了我最初想用ng-show做的事情。然而，ng-disabled实际上更适合我想要的。我添加了相关的css

style.css

.page-form-submit-page-submit {
display: block;
padding: 5px 15px;
border: none;
border-radius: 2px;
margin: 40px 400px 20px auto;
text-align: center;
background-color: #001F45;
color: #FFD200;
}
.page-form-submit-page-submit:active {
    background-color: #0250B0;
}

谁能解释一下如何让提交按钮显示后，所有字段都有效?