单选字段的HTML显示“请填写此字段”消息

Question

我有一个表单，有几个输入，一些文本，一些单选/下拉字段。所有字段都是必填字段。对于文本输入，我得到了一条很好的消息，说“填写这个字段”，但是对于Radio和Dropdown字段，消息没有显示。如何显示单选和下拉字段的错误消息？下面是我的代码：

<form action="" method="post" class="form" role="form">
  <div class="form-group required"><label class="form-control-label" for="name">Name:</label>
    <input class="form-control" id="name" name="name" required="" type="text" value="">
  </div>
  <!-- ^ this works  -->

  <div class="form-group required"><label class="form-control-label" for="gender">Gender</label>
    <div class="form-check">
        <input class="form-check-input" id="preference-0" name="preference" type="radio" value="male">
        <label class="form-check-label" for="preference-0">Male</label>
    </div>
    <div class="form-check">
        <input class="form-check-input" id="preference-1" name="preference" type="radio" value="female">
        <label class="form-check-label" for="preference-1">Female</label>
    </div>
    <div class="form-check">
        <input class="form-check-input" id="preference-2" name="preference" type="radio" value="other">
        <label class="form-check-label" for="preference-2">Other</label>
    </div>
  </div>
  <!-- ^ this does not work -->

  <div class="form-group required"><label class="form-control-label" for="choice">
    Please choose "A" or "B"</label>
      <select class="form-control" id="which_day" name="which_day" required="">
        <option value="a">A</option>
        <option value="b">B</option><
      </select>
  </div>
  <!-- ^ neither does this... -->
  
  <input class="btn btn-primary btn-md" id="submit" name="submit" type="submit" value="Next">
</form>

Answer 1

我现在弄明白了，至少你需要把"required“放在其中一个单选按钮/下拉框中，如下所示：

    <div class="form-check">
        <input class="form-check-input" id="preference-0" name="preference" type="radio" value="male" required>
        <label class="form-check-label" for="preference-0">Male</label>
    </div>

对于选择的字段，here是一个答案，它展示了如何做到这一点。