铁形式的addEventListener为null

Question

in relation to an already asked question here

But that question never got answered.

I am trying to addEventListener on an iron-form like:

my HTML imports:

<link rel="import" href="/bower_components/polymer/polymer.html">
<link rel="import" href="/bower_components/iron-ajax/iron-ajax.html">

<link rel="import" href="/bower_components/iron-form/iron-form.html">
<link rel="import" href="/bower_components/paper-input/paper-input.html">
<link rel="import" href="/bower_components/paper-button/paper-button.html">
<link rel="import" href="/bower_components/paper-spinner/paper-spinner.html">

the form:

<form is="iron-form" method="get" action="/" id="eventsDemo">
        <paper-input name="name" label="Name" required auto-validate></paper-input>
        <paper-input name="password" label="Password" type="password" required auto-validate></paper-input>
        <paper-checkbox name="read" required>You must check this box</paper-checkbox>
        <br>
        <paper-button raised onclick="_delayedSubmit(event)" disabled id="eventsDemoSubmit">
            <paper-spinner id="spinner" hidden></paper-spinner>
            Submit
        </paper-button>
        <paper-button raised onclick="_reset(event)">Reset</paper-button>
        <div class="output"></div>
    </form>

and the listener:

document.getElementById('eventsDemo').addEventListener('iron-form-submit', function (event) {

    });

But that gets me the error aswell -

Uncaught TypeError: Cannot read property 'addEventListener' of null

I already tried some suggestions with window.onload, or WebComponentsReady. Nothing helped.

Answer 1

也许您缺少}或Bower安装

Answer 2

I found the solution:

i defined the addEventListener on the wrong place and it needs to be with the shadowRoot in the connectedCallback().

 class UserApp extends Polymer.Element {
        static get is() {
            return 'user-app';
        }

        connectedCallback() {
            super.connectedCallback();

            let eventsDemo = this.shadowRoot.getElementById('eventsDemo');
            let eventsDemoSubmit = this.shadowRoot.getElementById('eventsDemoSubmit');

            eventsDemo.addEventListener('iron-form-submit', function (event) {
                console.log("iron form submit");

                eventsDemoSubmit.disabled = false;
                this.querySelector('.output').innerHTML = JSON.stringify(event.detail);
            });

            eventsDemo.addEventListener('change', function (event) {

                eventsDemoSubmit.disabled = !eventsDemo.validate;
            });
        }