How to pre-select a paper item from the drop-down menu from the model data?

Question

I have iron-formto do CRUDin my project. This works well except for one problem.

How can I get paper-dropdown-menuto display values ​​from model data? (That is: preselect paper-itemcorresponding to the value [[o.id]] from my model data)

The attribute selected paper-menudoes not help, because it is based on the index and not based on the value of a paper-item.

Here is the form code:

<form is="iron-form" id="itemForm" method="post" action="/api/item/edit">

    <input is="iron-input" name="id" type="hidden" value="{{item.id}}">

    <paper-dropdown-menu label="Title" selected-item="{{selectedTitle}}">
        <paper-menu class="dropdown-content">
            <template is="dom-repeat" items="{{titles}}" as="o">
                <paper-item value="[[o.id]]">[[o.name]]</paper-item>
            </template>
        </paper-menu>
    </paper-dropdown-menu>
    <input is="iron-input" name="title" type="hidden" value$="[[selectedTitle.value]]">

    <paper-input name="firstName" label="First name" value="{{item.firstName}}"></paper-input>

    <paper-button raised onclick="document.getElementById('itemForm').submit()">Save</paper-button>
</form>

Answer 1

-, selected-item , .

selected paper-menu, , -

<paper-menu id="menu" class="dropdown-content" selected="{{selectedValue}}" attr-for-selected="value">

, attr-for-selected, selected, . selectedValue , selected .

selectedValue Polymer ready, . , , selected , .

, ready, attached -

attached: function () {
  this.async(function () {
    this.selectedValue = 1;
  });
}

it .

Answer 2

paper-dropdown-menu, selected attr-for-selected , dropdown-content (, paper-menu paper-listbox).

<paper-dropdown-menu>
  <paper-listbox attr-for-selected="data-order" selected="1" class="dropdown-content">
    <paper-item data-order="0">First</paper-item>
    <paper-item data-order="1">Second</paper-item>
    <paper-item data-order="2">Third</paper-item>
  </paper-listbox>
</paper-dropdown-menu>