如何在表单提交中包含聚合物纸下拉菜单

Question

当我提交带有document.getElementById("form").submit(); 的 Polymer 表单时，firstName 和 lastName 包含在 POST 数据中，但纸张下拉菜单中的标题值不包含。缺少什么？

<form is="iron-form" id="form" method="post" action="/edit">
    <paper-dropdown-menu name="title" label="Title">
        <paper-menu class="dropdown-content">
            <template is="dom-repeat" items="{{titles}}" as="title">
                <paper-item value="{{item.id}}">{{title.name}}</paper-item>
            </template>
        </paper-menu>
    </paper-dropdown-menu>
    <paper-input name="firstName" label="First name"></paper-input>
    <paper-input name="lastName" label="Last name"></paper-input>
    <paper-button raised onclick="submitForm()">Save</paper-button>
</form>

编辑：

这是我完整的工作示例，非常感谢@Brandon 的回答：

<form is="iron-form" id="form" method="post" action="/api/edit">
    <paper-dropdown-menu label="Title" selected-item="{{selectedItem}}" selected-item-label="{{selected}}">
        <paper-menu class="dropdown-content">
            <template is="dom-repeat" items="{{titles}}" as="title">
                <paper-item value="[[title.id]]">[[title.name]]</paper-item>
            </template>
        </paper-menu>
    </paper-dropdown-menu>
    <input is="iron-input" name="title" type="hidden" value$="[[selectedItem.value]]">
    <paper-input name="firstName" label="First name"></paper-input>
    <paper-input name="lastName" label="Last name"></paper-input>
    <paper-button raised onclick="document.getElementById('form').submit()">Save</paper-button>
</form>

Answer 1

这可能会解决您的问题。创建一个隐藏的输入元素并将所选项目分配给隐藏元素的值。这为您提供了铁输入验证器的额外好处，可用于未来表单的多选。

<form is="iron-form" id="form" method="post" action="/edit">
    <paper-dropdown-menu label="Title" selected-item-label="{{selected}}">
        <paper-menu class="dropdown-content">
            <template is="dom-repeat" items="{{titles}}" as="title">
                <paper-item>{{title.name}}</paper-item>
            </template>
        </paper-menu>
    </paper-dropdown-menu>
    <input is="iron-input" name="title" type="hidden" value$="[[selected]]">
    <paper-input name="firstName" label="First name"></paper-input>
    <paper-input name="lastName" label="Last name"></paper-input>
    <paper-button raised onclick="submitForm()">Save</paper-button>
</form>