如何在 ng-if 和变量中使用过滤器？

在此示例中，我在ng-repeat https://docs.angularjs.org/api/ng/directive/ngRepeat，但是我如何在变量中使用它并且ng-if， 就像是：

{{languages.length | filter: {available: true}}}

and

ng-if="languages.length == 0 | filter: {available: true}"

See Fiddle http://jsfiddle.net/edwardtanguay/to7z06ma/.

HTML

<div ng-controller="mainController">
    <div>There are {{languages.length}} languages in total.</div>
    <div>??? There are {{languages.length}} languages available.</div>
    <div ng-if="languages.length == 0">??? Sorry, there are no languages available.</div>

    <ol>
        <li ng-repeat="language in languages | filter: {available: true}">{{language.name}}</li>
    </ol>
</div>

AngularJS

$scope.languages = [
    {id:1, name:"German", available: false},    
    {id:2, name:"English", available: true},    
    {id:3, name:"French", available: false},  
    {id:4, name:"Italian", available: true},  
    {id:5, name:"Spanish", available: false}
];

你能试试这个吗？

<div ng-controller="mainController">
    <div>There are {{languages.length}} languages in total.</div>
    <div>There are {{(languages|filter:{available:true}).length}} languages available.</div>
    <div ng-if="(languages|filter:{available:true}).length == 0">Sorry, there are no languages available.</div>

    <ol>
        <li ng-repeat="language in languages | filter: {available: true}">{{language.name}}</li>
    </ol>
</div>