polymer Dom-Repeat 绑定(bind)到内容

Question

在 polymer 1.2.3 中，dom-repeat 是否可能？使用内容作为模板并将值绑定(bind)到提供的元素？

自定义元素:

<dom-module id="modify-collection">
  <template>
    <div>
      <template is="dom-repeat" items="[[collection]]">
        <content></content>
      </template>
    </div>
  </template>
</dom-module>

用法:

<modify-collection collection="{{things}}">
  <list-item resource="[[item]]"></list-item>
</modify-collection>

我在没有帮助的情况下查看了以下资源:

Polymer: How to watch for change in <content> properties

Polymer 1.0 template bind ref equivalent

Data-binding between nested polymer elements

https://github.com/grappendorf/grapp-template-ref

https://github.com/Trakkasure/dom-bindref

https://github.com/Polymer/polymer/issues/1852

https://github.com/Polymer/polymer/pull/2196

2016 年 2 月 3 日更新 : 来自 polymer 团队 (PR #2196) ， future 计划对此提供更好的支持，以帮助解决一些缺点。

Answer 1

TLDR

解决方案 2 虽然有点冗长，但似乎效果最好。它还允许您动态选择模板，可能基于模型的属性。 (请参阅解决方案 2:高级示例)

背景故事

在这个简单的示例中发生了很多事情，包括模板化、在 shadow?、shady 和 light dom 之间“获取”内容，当然还有数据绑定(bind)。

这个问题提供了一些见解，但没有 Polymer 0.5's injectBoundHtml这不是真的可行(Using template defined in light dom inside a Polymer element)。问题是当我们尝试使用 innerHTML 将元素复制到我们的模板时，我们的数据绑定(bind)似乎丢失了(AFAIK)。

因此，如果没有它，我们就无法使用数据绑定(bind)动态创建我们的模板。因此，两种解决方案都提前将内容包装在模板中；这导致 html 是惰性的，并允许 Polymer 在适当的时间进行数据绑定(bind) (http://www.html5rocks.com/en/tutorials/webcomponents/template/)。

如果您真的想了解所有内容，我建议您阅读 Polymer src对于 lib/template/dom-repeat.html , lib/template/templatizer.html , lib/annotations/annotations.html (约 1500 行)。

解决方案 1 -

见 btelle's answer below对于改进的解决方案 1。

请注意，这种方法会导致 dom-repeat不自动渲染内容，所以我们手动调用渲染。

元素

<dom-module id="modify-collection">
  <template>
    <div>
      <content></content>
      <template id="repeater" is="dom-repeat" items="[[collection]]"></template>
    </div>
  </template>

  <script>
    ...
    ready: function() {
      this.$.repeater.templatize(this.querySelector('#templ'));
    }
    _changeCollection: function(item) {
      this.push('collection', item);
      this.$.repeater.render();
    }
  </script>
</dom-module>

用法

<modify-collection collection="{{things}}">
  <template id="templ"><list-item resource="[[item]]"></list-item></template>
</modify-collection>

解决方案 2

请注意，它的用法与元素 1 不同，因为 <template>必须有 is="dom-template"属性。

辅助元素

(此 PR 稍作修改: https://github.com/Polymer/polymer/pull/2196 ，最初基于 https://github.com/grappendorf/grapp-template-ref )

!--
@license
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Code distributed by Google as part of the polymer project is also
subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
-->
<!--
  Portions of this code have been adapted from the `grapp-template-ref` element.

  The original copyright notices are below.
-->
<!--
MIT License
Copyright (c) 2014-2015 Dirk Grappendorf, www.grappendorf.net

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THE SOFTWARE.
 -->

<!--

 The `dom-ref` element is a custom `HTMLTemplateElement` type extension that
can be used to reference another template by id using the `ref` property.
`dom-bindref` accepts a `bind` property to bind an object to the referenced
template. By default the bound object can be accessed as `item`, this can be
changed using the `as` property.

Example:

```html
<template is="dom-template" id="template-bind"><span>[[item.key]]</span></template>
<template is="dom-ref" ref="template-bind" bind='{"key":"value"}'></dom-ref>
```

-->
<!-- <link rel="import" href="templatizer.html"> -->

<script>

  Polymer({

    is: 'dom-ref',
    extends: 'template',

    /**
     * Fired whenever DOM is added or removed by this template (by
     * default, rendering occurs lazily).  To force immediate rendering, call
     * `render`.
     *
     * @event dom-change
     */

    properties: {

      /**
       * Reference to another template's id.
       */
      ref: {
        type: String,
        observer: '_refChanged'
      },

      /**
       * Object to be bound to referenced template.
       */
      bind: {
        type: Object,
        observer: '_bindChanged'
      },

      /**
       * The name of the variable to add to the binding scope for the
       * element associated with a given template instance.
       */
      as: {
        type: String,
        value: 'item'
      }
    },

    behaviors: [
      Polymer.Templatizer
    ],

    ready: function() {
      this.templatize(this);
    },

    attached: function() {
      return this._stamp();
    },

    detached: function() {
      return this._removeChildren();
    },

    _refChanged: function(newRef, oldRef) {
      if (oldRef) {
        this._removeChildren();
        return this._stamp();
      }
    },

    _bindChanged: function(newBind, oldBind) {
      if (oldBind) {
        this._removeChildren();
        return this._stamp();
      }
    },

    _stamp: function() {
      var root, template, templateRoot, bind = {};
      this._parent = Polymer.dom(this).parentNode;
      root = this._parent;

      while (Polymer.dom(root).parentNode) {
        root = Polymer.dom(root).parentNode;
      }
      template = Polymer.dom(root).querySelector("template#" + this.ref);

      // Check For Light Dom Elements that may be passed to this shadow root (Useful for: `<content></content>`)
      if (!template) {
        template = root.host.querySelector("template#" + this.ref);
      }

      // Check the whole document
      if (!template) {
        template = document.querySelector("template#" + this.ref);
      }
      bind[this.as] = this.bind;

      // templateRoot = template.stamp(bind).root;
      // Use this method until this lands: https://github.com/Polymer/polymer/pull/1889
      templateRoot = (new template.ctor(bind, template)).root;
      this._children = Array.prototype.slice.call(templateRoot.childNodes);
      return Polymer.dom(this._parent).insertBefore(templateRoot, this);
    },

    _removeChildren: function() {
      var child, i, len, ref, results;
      if (this._children) {
        ref = this._children;
        results = [];
        for (i = 0, len = ref.length; i < len; i++) {
          child = ref[i];
          results.push(Polymer.dom(this._parent).removeChild(child));
        }
        return results;
      }
    }

  });

</script>

元素

<dom-module id="modify-collection">
  <template>
    <div>
      <content></content>
      <template is="dom-repeat" items="[[collection]]">
          <template is="dom-ref" bind="[[item]]" ref="templ"></template>
      </template>
    </div>
  </template>
</dom-module>

用法

<modify-collection collection="{{things}}">
  <template id="templ" is="dom-template"><list-item resource="[[item]]"></list-item></template>
</modify-collection>

高级元素

用法不会从上面改变。

我们在这里所做的是引入一个间接级别，允许我们包装传递给我们元素的模板(在我们的示例中，使用覆盖)。

<dom-module id="modify-collection">
  <template>
    <div>
      <content></content>
      <template id="wrapper" is="dom-template">
        <div class="overlay">
          <template is="dom-ref" bind="[[item]]" ref="templ"></template>
        </div>
      </template>

      <template is="dom-repeat" items="[[collection]]">
        <template is="dom-ref" bind="[[item]]" ref="[[_templateRef(_overlayMode)]]"></template>
      </template>
    </div>
  </template>

  <script>
    ...
    properties: {
      _overlayMode: {
        type: Boolean,
        value: false
      }
    },
    _templateRef: function(overlayMode) {
      return overlayMode ? 'wrapper' : 'templ';
    }
  </script>
</dom-module>