javascript - Angularjs: select not updating when ng-model is updated

Question

I've created the following example so you can see exactly what is happening: http://jsfiddle.net/8t2Ln/101/

The same thing happens if I use ng-options. I have a different reason for doing it this way, but for the simplification of the example left that part out.

As you can see it has by default two options. I'm displaying the selected value of the ng-model next to the select so you can see what it is. When you use the top piece to add a third option it sets the value to the value of that new option as is evidenced by the displayed ng-model value next to the select, but the select itself doesn't change to show the correct value selected.

Below is the sample code at the link:

var testApp = angular.module('testApp', ['ngRoute']);

testApp.controller('Ctrl', function ($scope) {

    $scope.newInput = '';
    $scope.inputDevice = [
        {
            value: '1',
            label: 'input1'
        },
        {
            value: '2',
            label: 'input2'
        }
    ];
    $scope.selectedDevice = '';

    $scope.addType = function () {
        var newElem = {
            label: $scope.newInput,
            value: '3'
        };
        $scope.inputDevice.push(newElem);
        $scope.selectedDevice = newElem.value;
    };


});

And here is the html:

<div ng-app="testApp">
    <div ng-controller="Ctrl">
        <p>
            <input type="text" ng-model="newInput" />
            <br />
            <button ng-click="addType()">Add Type</button>
        </p>
        <select ng-model="selectedDevice">
            <option></option>
            <option ng-repeat="i in inputDevice" value="{{ i.value }}">{{ i.label }} - {{ i.value }}</option>
        </select>
        {{ selectedDevice }}</div>
</div>

Answer 1

This is exactly why you should not use ngRepeat to render select options. You should use ngOptions instead:

<select ng-model="selectedDevice" 
        ng-options="i.value as (i.label + '-' + i.value) for i in inputDevice">
    <option></option>
</select>

In general, avoid using ngRepeat for rendering select options. There are at least two good reasons. ngRepeat creates separate child scope per iteration, which is not needed in case of option tag. Another important caveat is that with ngRepeat you can only bind select to primitives like strings, but you won't be able to write object to ngModel with it.

Here is a demo below.

angular.module('demo', []).controller('DemoController', function($scope) {

    $scope.newInput = '';
    $scope.inputDevice = [
    {value: '1', label: 'input1'}, 
        {value: '2', label: 'input2'}
    ];
    
    $scope.selectedDevice = '';
    $scope.addType = function() {
        var newElem = {
            label: $scope.newInput,
            value: Number($scope.inputDevice[$scope.inputDevice.length - 1].value) + 1
        };
        $scope.inputDevice.push(newElem);
        $scope.selectedDevice = newElem.value;
        $scope.newInput = '';
    };

});

<script src="https://cdnjs.cloudflare.com/ajax/libs/angular.js/1.4.8/angular.min.js"></script>
<div ng-app="demo" ng-controller="DemoController">
    <form ng-submit="addType()">
        <input type="text" ng-model="newInput" />
        <button type="submit">Add Type</button>
    </form>
    <select ng-model="selectedDevice" ng-options="i.value as (i.label + ' - ' + i.value) for i in inputDevice">
        <option>Select</option>
    </select>
    {{ selectedDevice }}
</div>