dart - polymer Dart 传递元素作为属性

Question

感觉，我一个月前对Polymer 0.5提出的所有问题都再次由1.0提出...
我有一个自定义元素，该元素定义了一个属性，该属性我想采用一个Element以便以后可以使用它。

@HtmlImport('test_animation.html')
library test.animation

import 'dart:html';
import 'dart:js';
import 'package:polymer/polymer.dart';
import 'package:web_components/web_components.dart' show HtmlImport;
import 'package:test/log.dart';
import 'dart:async';

// @jsProxyReflectable
@PolymerRegister('test-animation')
class TestAnimation extends PolymerElement {

  @Property(observer: 'targetChanged')
  Object target = null;

  factory TestAnimation() => new Element.tag('test-animation');

  TestAnimation.created() : super.created() {
    Log.d(tag: 'Animation', message: 'Animation created with target "$target"');
  }

  //@eventHandler
  @reflectable
  void targetChanged([newValue, oldValue]) {
    Log.d(tag: 'Animation', message: 'Target changed from "$oldValue" to "$newValue"');
    Log.d(tag: 'Animation', message: 'Target is now "$target"');
  }
}

我使用以下代码创建元素:

<div id="buttonContainer">
    <paper-button id="loginButton" on-click="login">Login</paper-button>
    <paper-toast id="errorToast" text="Incorrect username or password."></paper-toast>
</div>

<test-animation target="{{$['loginButton']}}"></test-animation>

我的控制台输出是:

Animation: Target changed from "null" to "null"

Animation: Target is now "null"

Animation: Animation created with target "null"

这是为什么？如何传递元素？ -或者这还不可能吗？

Answer 1

从https://www.polymer-project.org/1.0/docs/devguide/data-binding.html#path-binding:

The path syntax doesn’t support array-style accessors (such as users[0].name). However, you can include indexes directly in the path (users.0.name).

因此，您应该能够将$['loginButton']更改为$.loginButton，然后它应该可以工作。