使用querySelector查找Polymer模板内的嵌套元素将返回null [英] Using querySelector to find nested elements inside a Polymer template returns null
问题描述
我正在尝试在新元素（tabs-list）中使用paper-tabs但是在打印选项卡之后我无法使用querySelector来更改所选的。
I'm trying to use paper-tabs inside new element (tabs-list) but after print tabs I can't use querySelector to change selected one.
元素代码（没有样式）：
Element code (without style):
<link rel="import" href="../components/polymer/polymer.html">
<link rel="import" href="../sprint-service/sprint-service.html">
<link rel="import" href="../components/paper-tabs/paper-tabs.html">
<polymer-element name="tab-list" attributes="show">
<template>
<sprint-service id="service" sprints="{{sprints}}"></sprint-service>
<paper-tabs selected="all" valueattr="name" self-end>
<paper-tab name="all">ALL</paper-tab>
<template repeat="{{sprint in sprints}}">
<paper-tab name="{{sprint.id}}">{{sprint.id}}</paper-tab>
</template>
</paper-tabs>
</template>
<script>
Polymer('tab-list', {
ready: function() {
var tabs = document.querySelector('paper-tabs');
tabs.addEventListener('core-select', function() {
list.show = tabs.selected;
})
}
});
</script>
</polymer-element>
Index.html代码（whitout样式）：
Index.html code (whitout style):
<!doctype html>
<html>
<head>
<title>unquote</title>
<meta name="viewport" content="width=device-width, minimum-scale=1.0, initial-scale=1.0, user-scalable=yes">
<script src="../components/platform-dev/platform.js"></script>
<link rel="import" href="../components/font-roboto/roboto.html">
<link rel="import"
href="../components/core-header-panel/core-header-panel.html">
<link rel="import"
href="../components/core-toolbar/core-toolbar.html">
<link rel="import" href="tab-list.html">
<link rel="import" href="post-list.html">
</head>
<body unresolved touch-action="auto">
<core-header-panel>
<core-toolbar>
<tab-list></tab-list>
</core-toolbar>
<div class="container" layout vertical center>
<post-list show="all"></post-list>
</div>
</core-header-panel>
<script>
var list = document.querySelector('post-list');
</script>
</body>
</html>
但是
querySelector('paper-tabs') = *null*
我试过将 eventListener 放在 index.html 中，但我遇到了同样的问题。
谁能告诉我问题在哪里？
I've tried to put the eventListener in index.html but I have the same problem.
can anyone tell me where the problem is?
非常感谢！
推荐答案
document.querySelector('paper-tabs');
找不到 paper-tabs 元素，因为它是隐藏的在 tab-list 元素的shadow DOM内。
doesn't find the paper-tabs element, because it is hidden inside the shadow DOM of the tab-list element.
你可以简单地给 paper-tabs 一个id，说标签，然后像这样访问它
You can simply give paper-tabs an id, say tabs, and access it like so
this.$.tabs
（参见 http://www.polymer-project.org/docs/polymer/polymer.html#automatic-node-finding 。）
还可以选择直接访问shadow DOM
There is also the option to access the shadow DOM directly
this.shadowRoot.querySelector('paper-tabs');
如果您只想在 paper-tabs 选项上收听更改，您可以使用更改观察器：
If you only want to listen for changes on the paper-tabs selection, you can use a change watcher:
<paper-tabs selected="{{currentTab}}">
Polymer('tab-list', {
currentTab: 'all',
currentTabChanged: function() {
console.log(this.currentTab);
}
});
（参见 http://www.polymer-project.org/docs/polymer/polymer.html#change-watchers ）
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