jquerymobile对话框中缺少标题栏

我在手机中显示以下对话框

但当它出现时，标题栏不会显示。 当我检查代码时，我在类中看不到任何“.ui头”

这里是对话框的div

  <div id="pagepassword" data-role="dialog" data-title="Change password">
      <div class="ui-content" data-role="content"  role="main">

             <form id="formpassword" action="" method="post" onsubmit="" data-ajax="false">

                <div data-role="fieldcontain" class="ui-field-contain ui-body ui-br">
                  <label for="password" class="ui-input-text">Old password/label>
                  <input type="password" name="o_password" id="o_password" value="" class="ui-input-text ui-body-c ui-corner-all ui-shadow-inset" autocomplete="off" class="required">
                </div>

                <div data-role="fieldcontain" class="ui-field-contain ui-body ui-br">
                  <label for="password" class="ui-input-text">New password</label>
                  <input type="password" name="n_password" id="n_password" value="" class="ui-input-text ui-body-c ui-corner-all ui-shadow-inset" autocomplete="off" class="required">
                </div>

                <div data-role="fieldcontain" class="ui-field-contain ui-body ui-br">
                  <label for="password" class="ui-input-text">Confirm new password</label>
                  <input type="password" name="c_password" id="c_password" value="" class="ui-input-text ui-body-c ui-corner-all ui-shadow-inset" autocomplete="off" class="required">
                </div>


                <fieldset class="ui-grid-solo">
                  <div class="ui-block-a">
                         <button id="submit" type="submit" data-theme="b" class="ui-btn-hidden" aria-disabled="false">Submit</button>
                 </div>
                </fieldset>
              </form>


    </div>
</div>

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新密码
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有人知道我检查对话框时为什么缺少.ui头吗

谢谢