在AngularJS BootstrapUI Typeahead,什么是$viewValue？

<div class="container">
    <div ng-controller="mainCtrl" class="row-fluid">
        <form class="row-fluid">
            <div class="container-fluid">
                <input type="text" ng-model="SELEcted" typeahead="state for state in states | filter:$viewValue" />
            </div>
        </form>
    </div>
</div>

<script>
angular.module('myApp',['ui.bootstrap'])
.controller("mainCtrl",function ($scope) {
   $scope.SELEcted = '';
   $scope.states = ['Alabama','Alaska','Arizona','Arkansas','California','Colorado','Connecticut','Delaware','Florida','Georgia','Hawaii','Idaho','Illinois','Indiana','Iowa','Kansas','Kentucky','Louisiana','Maine','Maryland','Massachusetts','Michigan','Minnesota','Mississippi','Missouri','Montana','Nebraska','Nevada','New Hampshire','New jersey','New Mexico','New York','North Dakota','North Carolina','Ohio','Oklahoma','Oregon','Pennsylvania','Rhode Island','South Carolina','South Dakota','Tennessee','Texas','Utah','Vermont','Virginia','Washington','West Virginia','Wisconsin','Wyoming'];
});
</script>

http://jsfiddle.net/alfrescian/ZjPWe/

$ viewValue是视图中的当前值 – 您的字符串输入。 $ viewValue在ngModel中指定。