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.
@published int data = 0;
<input type="number" value="{{data}}">
Obviously, a reference of String is getting stored in what is supposed to be an integer.
I tried to use filter to solve this issue, but still could get it to work:
int integerize(Object a) {
int ret = 0;
if (a is String) {
try {
ret = int.parse(a);
} on FormatException catch (e) {
}
} else if( a is int) {
ret = a;
}
return ret;
}
<input type="number" value="{{data | integerize}}">
So I switched to not using binding for this. Can somebody suggest a better, efficient solution using binding?
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}}">
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>
