聚合物1.x：如何反转由< firebase-collection>返回的记录顺序 [英] Polymer 1.x: How to reverse order of records returned by <firebase-collection>
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问题描述
如何反转由<$返回的记录的顺序c $ c>< firebase-collection> ，如下所示：
How do I reverse the order of records returned by <firebase-collection> as follows:
<firebase-collection id="foo" order-by-child="bar">
？
我可以声明？或者，我需要调用一个命令式的方法，如可能......
Can I do it declaratively? Or do I need to call an imperative method like maybe...
this.$.foo = this.$.foo.reverse();
https://elements.polymer-project.org/elements/firebase-element?active=firebase-collection
注意：我使用< iron-list> 而不是< template =dom-repeat> 。
推荐答案
最好的解决方案是使用< iron-list> 然后根据这个答案进行排序。 p>
http://jsbin.com/vizexodoyi/1/edit?html,output
The best solution is to use <iron-list> then sort that according to this answer.
<html>
<head>
<title>My Element</title>
<script data-require="polymer@*" data-semver="1.0.0" src="http://www.polymer-project.org/1.0/samples/components/webcomponentsjs/webcomponents-lite.js"></script>
<script data-require="polymer@*" data-semver="1.0.0" src="http://www.polymer-project.org/1.0/samples/components/polymer/polymer.html"></script>
<base href="http://element-party.xyz/" />
<link rel="import" href="all-elements.html" />
</head>
<body>
<dom-module id="my-element">
<template>
<style>
h3 {
margin-bottom: 0px;
}
iron-list {
padding-bottom: 16px;
height: 100%;
}
.item {
@apply(--layout-horizontal);
margin: 16px 16px 0 16px;
padding: 20px;
border-radius: 8px;
background-color: white;
border: 1px solid #ddd;
}
</style>
<firebase-collection location="https://dinosaur-facts.firebaseio.com/dinosaurs" data="{{items}}">
</firebase-collection>
<h3>Controls</h3>
<paper-dropdown-menu label="Sort by">
<paper-menu class="dropdown-content" selected="{{sortVal}}" attr-for-selected="data-sortby">
<paper-item data-sortby="order">Order</paper-item>
<paper-item data-sortby="height">Height</paper-item>
</paper-menu>
</paper-dropdown-menu>
<br>
<paper-toggle-button checked="{{reverse}}">Reverse</paper-toggle-button>
<br /><br />
<br><h3>Monitor Control Values</h3>
<div>Sort by: [[sortVal]]</div>
<div>Reverse: [[reverse]]</div>
<br><h3>Iron-List Output</h3>
<iron-list id="list" items="[[items]]" as="item">
<template>
<div class="item">
Name: [[item.__firebaseKey__]]<br />
Order: [[item.order]]<br />
Height: [[item.height]]
</div>
</template>
</iron-list>
</template>
<script>
(function() {
Polymer({
is: "my-element",
properties: {
items: {
type: Array,
},
sortVal: {
type: String,
value: 'order'
},
sortOrder: {
type: Number,
value: -1, // High to low
computed: '_computeSortOrder(reverse)'
}
},
observers: [
'sortChanged(sortVal, sortOrder)'
],
_computeSortOrder: function(bool) {
return bool ? 1 : -1;
},
sortChanged(val, ord) {
if (! this.items || this.items.length == 0) {
return;
}
var temp = Array.prototype.slice.call(this.items);
temp.sort(this._computeSort(val, ord));
this.items = temp;
//console.log('ord: ' + ord);
//console.log('val: ' + val);
//console.log('items: ' + this.items);
},
_computeSort: function(val, ord) {
return function(a, b) {
if (a[val] === b[val]) {
return 0;
}
return (ord * (a[val] > b[val] ? 1 : -1));
};
}
});
})();
</script>
</dom-module>
<my-element></my-element>
</body>
</html>
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