Question

为了便于说明，我创建了一个继承自WebComponent的类FancyOption，该类在单击另一个子元素时更改为由一个子元素中的文本指定的背景颜色。

import 'package:web_ui/web_ui.dart';
import 'dart:html';

class FancyOptionComponent extends WebComponent {
  ButtonElement _button;
  TextInputElement _textInput;

  FancyOptionComponent() {
    // obtain reference to button element
    // obtain reference to text element

    // failed attempt
    //_button = this.query('.fancy-option-button');
    // error: Bad state: host element has not been set. (no idea)

    // make the background color of this web component the specified color
    final changeColorFunc = (e) => this.style.backgroundColor = _textInput.value;
    _button.onClick.listen(changeColorFunc);
  }
}

FancyOption HTML：

<!DOCTYPE html>

<html>
  <body>
    <element name="x-fancy-option" constructor="FancyOptionComponent" extends="div">
      <template>
        <div>
          <button class='fancy-option-button'>Click me!</button>
          <input class='fancy-option-text' type='text'>
        </div>
      </template>
      <script type="application/dart" src="fancyoption.dart"></script>
    </element>
  </body>
</html>

我在这样的页面上有三个。

<!DOCTYPE html>

<html>
  <head>
    <meta charset="utf-8">
    <title>Sample app</title>
    <link rel="stylesheet" href="myapp.css">
    <link rel="components" href="fancyoption.html">
  </head>
  <body>
    <h3>Type a color name into a fancy option textbox, push the button and 
    see what happens!</h3>

    <div is="x-fancy-option" id="fancy-option1"></div>
    <div is="x-fancy-option" id="fancy-option2"></div>
    <div is="x-fancy-option" id="fancy-option3"></div>

    <script type="application/dart" src="myapp.dart"></script>
    <script src="packages/browser/dart.js"></script>
  </body>
</html>

Answer 1

只需使用getShadowRoot()并对其进行查询：

import 'package:web_ui/web_ui.dart';
import 'dart:html';

class FancyOptionComponent extends WebComponent {
  ButtonElement _button;
  TextInputElement _textInput;

  inserted() {
    // obtain references
    _button = getShadowRoot('x-fancy-option').query('.fancy-option-button');
    _textInput = getShadowRoot('x-fancy-option').query('.fancy-option-text');

    // make the background color of this web component the specified color
    final changeColorFunc = (e) => this.style.backgroundColor = _textInput.value;
    _button.onClick.listen(changeColorFunc);
  }
}

其中x-fancy-option字符串是元素的名称。

注意：我将构造函数更改为inserted()方法，which is a life cycle method。

Answer 2

我知道_root是被剥夺了。推荐_root的答案应该使用getShadowRoot（）代替_root。

Dart Web组件如何获得对其子代的引用？

2 个答案: