Angularjs ng-options using number for model does not select initial value

问题

I'm trying to use ng-options with a <select> to bind a numeric integer value to a list of corresponding options. In my controller, I have something like this:

myApp.controller('MyCtrl', function() {
    var self = this;

    var unitOptionsFromServer = {
        2: "mA",
        3: "A",
        4: "mV",
        5: "V",
        6: "W",
        7: "kW"
    };

    self.unitsOptions = Object.keys(unitOptionsFromServer).map(function (key) {
        return { id: key, text: unitOptionsFromServer[key] };
    });

    self.selectedUnitOrdinal = 4; // Assume this value came from the server.
});

HTML:

<div ng-controller="MyCtrl as ctrl">
    <div>selectedUnitOrdinal: {{ctrl.selectedUnitOrdinal}}</div>
    <select ng-model="ctrl.selectedUnitOrdinal" ng-options="unit.id as unit.text for unit in ctrl.unitsOptions"></select>
</div>

And here's a jsFiddle demonstrating the problem, and some other approaches I've taken but am not happy with.

The select option is being initialized with an empty value, instead of "mV" as expected in this example. The binding seems to work fine if you select a different option -- selectedUnitOrdinal updates properly.

I've noticed that if you set the initial model value to a string instead of a number, then the initial selection works (see #3 in the fiddle).

I really would like ng-options to play nice with numeric option values. How can I achieve this elegantly?

回答1:

Angular's documentation for the ng-select directive explains how to solve this problem. See https://code.angularjs.org/1.4.7/docs/api/ng/directive/select (last section).

You can create a convert-to-number directive and apply it to your select tag:

JS:

module.directive('convertToNumber', function() {
  return {
    require: 'ngModel',
    link: function(scope, element, attrs, ngModel) {
      ngModel.$parsers.push(function(val) {
        return val != null ? parseInt(val, 10) : null;
      });
      ngModel.$formatters.push(function(val) {
        return val != null ? '' + val : null;
      });
    }
  };
});

HTML:

<select ng-model="model.id" convert-to-number>
  <option value="0">Zero</option>
  <option value="1">One</option>
  <option value="2">Two</option>
</select>

Note: I found the directive from the doc does not handle nulls so I had to tweak it a little.

回答2:

Maybe it's a bit messy, but result can be achieved without special functions right in ng-options

<select ng-model="ctrl.selectedUnitOrdinal" ng-options="+(unit.id) as unit.text for unit in ctrl.unitsOptions"></select>

回答3:

It's because when you get the unit.id it's returning a string not an integer. Objects in javascript store their keys as strings. So the only way to do it is your approach of surrounding 4 by quotations.

Edit

<select ng-model="ctrl.selectedUnitOrdinal" ng-options="convertToInt(unit.id) as unit.text for unit in ctrl.unitsOptions"></select>

$scope.convertToInt = function(id){
    return parseInt(id, 10);
};

回答4:

You can also define filter number, this filter will automatically parse string value to int:

<select ng-model="ctrl.selectedUnitOrdinal" ng-options="unit.id|number as unit.text for unit in ctrl.unitsOptions"></select>


angular.module('filters').filter('number', [function() {
        return function(input) {
            return parseInt(input, 10);
        };
    }]);

回答5:

Just to add Christophe's answear: easiest way to achive and maintaint it is to make a directive:

JS:

.directive('convertToNumber', function() {
  return {
    require: 'ngModel',
    link: function(scope, element, attrs, ngModel) {
      ngModel.$parsers.push(function(val) {
        //saves integer to model null as null
        return val == null ? null : parseInt(val, 10);
      });
      ngModel.$formatters.push(function(val) {
        //return string for formatter and null as null
        return val == null ? null : '' + val ;
      });
    }
  };
});

Christophe's answear wont work correctly for '0' as it returns false on "val?" test.

回答6:

I think the other solutions are overly complex for simply establishing the value as an integer. I would use:

<select ng-model="model.id">
    <option ng-value="{{ 0 }}">Zero</option>
    <option ng-value="{{ 1 }}">One</option>
    <option ng-value="{{ 2 }}">Two</option>
</select>

回答7:

Angular is seeing your id property as a string, add quotes:

self.selectedUnitOrdinal = "4";

回答8:

Very similarly to tymeJV's answer, simple workaround is to convert the default selection number to a string like this:

self.selectedUnitOrdinal = valueThatCameFromServer.toString();

This way, you don't have to hardcode the number, you can just convert any received value. It's an easy fix without any filters or directives.

回答9:

<select ng-model="ctrl.selectedUnitOrdinal" ng-options="+(unit.id) as unit.text for unit in ctrl.unitsOptions"></select>

回答10:

Make id property in unitsOptions as number

self.unitsOptions = Object.keys(unitOptionsFromServer).map(function (key) {
        return { id: +key, text: unitOptionsFromServer[key] };
    });

http://jsfiddle.net/htwc10nx/

回答11:

While the solution provided by Mathew Berg works it will probably break other selects that use sting-valued select options. This may be a problem if you try to write one universal directive for handling selects (like I did).

A nice workaround is to check if the value is a number (even if it is a string containing a number) and only than do the conversion, like so:

angular.module('<module name>').filter('intToString', [function() {
        return function(key) {
            return (!isNaN(key)) ? parseInt(key) : key;
        };
    }]);

or as a controller method:

$scope.intToString = function(key) {
    return (!isNaN(key)) ? parseInt(key) : key;
};

回答12:

You can use ng-value attribute. Like this:

<select ng-model="model.id">
  <option ng-value="0">Zero</option>
  <option ng-value="1">One</option>
  <option ng-value="2">Two</option>
</select>

来源：https://stackoverflow.com/questions/28114970/angularjs-ng-options-using-number-for-model-does-not-select-initial-value