是否有聚合物模板的印章事件？ [英] Is there a stamp event for polymer templates?

问题描述

我试图在每次标记其内容时将输入元素聚焦在聚合物模板内。问题是在模板加载之前我无法选择输入元素。目前，我只是在模板加载后使用setTimeout来聚焦输入100ms，但我想知道是否有更优雅的解决方案。此外，自动聚焦属性不起作用，因为模板可能会多次取消标记和重新标记。现在，我的代码看起来像这样（这是在聚合物元素定义中）：

I am trying to focus an input element inside of a polymer template every time it stamps its contents. The problem is that I cannot select the input element until the template has loaded. Currently, I am just using setTimeout to focus the input 100ms after the template should load, but I want to know if there is a more elegant solution. Also, the autofocus attribute doesn't work, because the template may un-stamp and re-stamp many times. Right now, my code looks something like this (this is inside a polymer element definition):

Polymer({

  // ...

  showInput: false,

  makeInputVisible: function() {
    this.showInput = true;
    var container = this.$.container;
    setTimeout(function() {
      container.querySelector("#input").focus();
    }, 100);
  },
});

<div id="container">
  <template if="{{showInput}}">
    <input id="input" is="core-input" committedValue="{{inputValue}}" />
  </template>
</div>

但我更喜欢这样的东西：

But I would prefer something more like this:

Polymer({

  // ...

  showInput: false,

  makeInputVisible: function() {
    this.showInput = true;
  },

  focusInput: function() {
    this.$.container.querySelector("#input").focus();
  },
});

<div id="container">
  <template if="{{showInput}}"
            on-stamp="{{focusInput}}">
    <input id="input" is="core-input" committedValue="{{inputValue}}" />
  </template>
</div>

任何想法都表示赞赏。

推荐答案

使用Polymer 1.0，模板在标记时会触发dom-change事件。但是，使用dom-if模板会产生显着的性能成本，因为它们需要操作dom树。做这样的事情要好得多：

With Polymer 1.0, there is a 'dom-change' event fired by templates when they stamp. However, there is a significant performance cost to using dom-if templates since they need to manipulate the dom tree. It would be much better to do something like this:

<div id="container">
  <input id="input" hidden="[[!showInput]]" value="{{inputValue::input}}">
</div>

observers: [
  '_showInputChanged(showInput)',
],

_showInputChanged: function (showInput) {
  if (showInput) {
    this.$.input.focus();
  }
},

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