Question

我遇到了Dart 1.16.0 + Polymer的奇怪问题。要执行计算，需要将double类型输入参数转换为字符串，然后再将其转换为double以进行计算，否则将引发无效的参数异常。任何人都可以指出我可能出错的地方吗？

HTML code， stats.html

        <div class="container flex-horizontal">
            <div class="flexchild-horizontal">
                <div class="container flex-horizontal">
                    <div class="flexchild-horizontal">Base</div>
                    <div><input type="text" name="base" value="{{base::input}}" size="5" maxlength="5"></div>
                </div>
            </div>
            <div class="flexchild-horizontal">
                <div class="container flex-horizontal">
                    <div class="flexchild-horizontal">Calculated Value</div>
                    <div><input type="text" name="calc_value" value="{{calculateValue(base)}}" size="5" maxlength="5"></div>
                </div>
            </div>

Dart代码， stats.dart

@HtmlImport('stats.html')
library workbench.lib.client.stats;

import 'package:web_components/web_components.dart' show HtmlImport;
import 'package:polymer/polymer.dart';
import 'package:polymer_elements/paper_material.dart';
import 'package:polymer_elements/paper_styles.dart';
import 'package:polymer_elements/iron_flex_layout.dart';

@PolymerRegister('stats')
class Stats extends PolymerElement {

  @property(notify: true)
  double base = 10.0;

  //@Property(computed: 'calculateValue(base)')
  //double value;

  Stats.created() : super.created();

  @reflectable
  double calculateValue(double b) {
    print("Base is ");
    print(b);

    // Not working. Throw an invalid Argument: 5.0 Exception
    // var c = b + 5.0;

    // Working
    var c = double.parse(b.toString()) + 5.0;
    print("c is ");
    print(c);

    return c;
  }

  ready() {

  }
}

Answer 1

我猜你需要使用num代替double。至少在Dartium中，据我所知5.0将int返回，而不是double。这是因为在JS中，int和double之间没有区别。

int和double之间的正确区分仅适用于服务器（独立VM）。只要没有从JS传递值，它也适用于Dartium。

Dart + Polymer中的算术运算会引发无效的参数异常

1 个答案: