Polymer dart: Data bind integer value to String attribute

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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.

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囚心锁ツ

2020-12-22 01:09

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.

<!DOCTYPE html>
<dom-module id='app-element'>
  <template>
    <style>
      input:invalid {
        border: 3px solid red;
      }
    </style>
    <input type="number" value="[[intValue]]"
           on-input="convertToInt" notify-path="intValue">

    <!-- a 2nd element just to demonstrate that 2-way-binding -->
    <input type="number" value="[[intValue]]"
           on-input="convertToInt" notify-path="intValue">
  </template>
</dom-module>

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

<input type="number" value="{{intValue::input}}">

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

<input type="number" value="{{intValue::change}}">

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时光说笑

2020-12-22 01:12

This is for Polymer <= 0.16. For Polymer >= 1.0 see my other answer.

HTML attributes store only string values. What you could do is to use a getter/setter for binding and parse when the value is set.

@observable
int data;

@ComputedProperty('data') // haven't tried this but should work - see comments on http://japhr.blogspot.co.at/2014/08/whats-difference-between-attribute-and.html
@observable
get dataValue => data;
set dataValue(val) {
  if(val == null) {
    data = 0;
  } else if(val is num) {
    data = val.toInt();
  } else if(val is String) {
    data = num.parse(val, (v) => 0).toInt();
  } else {
    data = 0;
  }
}

or use a transformer or custom Polymer expressions
like explained in polymer dart input binding int properties

Alternative approache uses Dart Polymer 1.0 (also possible with Dart Polymer 0.16)

app_element.dart

@HtmlImport('app_element.html')
library _template.web.app_element;

import 'dart:html' as dom;
import 'package:web_components/web_components.dart' show HtmlImport;
import 'package:polymer/polymer.dart';

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

  @property int intValue;
  @property String stringValue;

  @reflectable
  valueInputHandler(dom.Event event, [_]) {
    var input = (event.target as dom.NumberInputElement);
    var value = input.valueAsNumber;
    if (!value.isNaN && !value.isInfinite) {
      set('intValue', value.toInt());
      input.setCustomValidity('');
    } else {
      // just to get the `:invalid` pseudo-class for styling
      input.setCustomValidity('Not a number.');
    }
  }
}

app_element.html

<!DOCTYPE html>
<dom-module id='app-element'>
  <template>
    <style>
      input:invalid {
        border: 3px solid red;
      }
    </style>
    <input type="number"
           value="{{stringValue::input}}"
           on-input="valueInputHandler" >
    <div>stringValue: <span>{{stringValue}}</span></div>
    <div>intValue:<span>{{intValue}}</span></div>
  </template>
</dom-module>

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