Polymer dart: Data bind integer value to String attribute

Question

I am trying to bind an integer to a String attribute. To say exactly, I am trying to bind a published integer variable to the value attribute of the text input element.

Answer 1

For Polymer 1.0.0 this worked fine for me

Create a reusable behavior or just add the convertToNumeric() to your Polymer element:

@HtmlImport('app_element.html')
library app_element;
import 'dart:html' as dom;
import 'package:web_components/web_components.dart' show HtmlImport;
import 'package:polymer/polymer.dart';

@behavior
abstract class InputConverterBehavior implements PolymerBase {
  @reflectable
  void convertToInt(dom.Event e, _) {
    final input = (e.target as dom.NumberInputElement);
    double value = input.valueAsNumber;
    int intValue =
        value == value.isInfinite || value.isNaN ? null : value.toInt();
    notifyPath(input.attributes['notify-path'], intValue);
  }
}

Apply the behavior to your element:

@PolymerRegister('app-element')
class AppElement extends PolymerElement with InputConverterBehavior {
  AppElement.created() : super.created();

  @property int intValue;
}

In HTML of your element configure the input element:

• bind value to your property: value="[[intValue]]" so the input element gets updated when the property changes
• set up event notification to call the converter when the value changes on-input="convertToNumeric" notify-path="intValue" where intValue is the name of the property to update with the numeric value.

---

An alternative approach

Create a property as getter/setter:

  int _intValue;
  @property int get intValue => _intValue;
  @reflectable set intValue(value) => convertToInt(value, 'intValue');

Create a behavior or add the function directly to your element

@behavior
abstract class InputConverterBehavior implements PolymerBase {
  void convertToInt(value, String propertyPath) {
    int result;
    if (value == null) {
      result = null;
    } else if (value is String) {
      double doubleValue = double.parse(value, (_) => double.NAN);
      result =
          doubleValue == doubleValue.isNaN ? null : doubleValue.toInt();
    } else if (value is int) {
      result = value;
    } else if (value is double) {
      result =
          value == value.isInfinite || value.isNaN ? null : value.toInt();
    }
    set(propertyPath, result);
  }
}

This way you can use the same markup as for text input fields

or if you want to delay the update of the property until the input field is left