指令中的AngularJS模板不显示文本

Question

我尝试在angularjs中创建指令：

JavaScript和HTML代码：

'use strict';

var app = angular.module('myApp', ['app.directives']);

app.controller('AppCtrl', function($scope){                     
    $scope.roles = [
          {"id": 1, "name": "Michael"},
          {"id": 2, "name": "Max"},
          {"id": 3, "name": "John"}
    ];
    
    
    $scope.dummyData = "Dummy!!!";
    $scope.member = {roles: []};
    $scope.selected_items = [];
});

var app_directives = angular.module('app.directives', []);

app_directives.directive('dropdownMultiselect', function(){
   return {
       restrict: 'E',
       scope:{  
            testElem: '=',
            model: '=',
            options: '=',
            pre_selected: '=preSelected'
       },
       template: "<div class='btn-group' data-ng-class='{open: open}'>"+
        "<button class='btn btn-small'>{{testElem}}</button>"+
                "<button class='btn btn-small dropdown-toggle' data-ng-click='open=!open;openDropdown()'><span class='caret'></span></button>"+
                "<ul class='dropdown-menu' aria-labelledby='dropdownMenu'>" + 
                    "<li><a data-ng-click='selectAll()'><i class='icon-ok-sign'></i>  Check All</a></li>" +
                    "<li><a data-ng-click='deselectAll();'><i class='icon-remove-sign'></i>  Uncheck All</a></li>" +                    
                    "<li class='divider'></li>" +
                    "<li data-ng-repeat='option in options'> <a data-ng-click='setSelectedItem()'>{{option.name}}<span data-ng-class='isChecked(option.id)'></span></a></li>" +                                        
                "</ul>" +
            "</div>" ,
       controller: function($scope){
           
           $scope.openDropdown = function(){        
                    $scope.selected_items = [];
                    for(var i=0; i<$scope.pre_selected.length; i++){                        $scope.selected_items.push($scope.pre_selected[i].id);
                    }                                        
            };
           
            $scope.selectAll = function () {
                $scope.model = _.pluck($scope.options, 'id');
                console.log($scope.model);
            };            
            $scope.deselectAll = function() {
                $scope.model=[];
                console.log($scope.model);
            };
            $scope.setSelectedItem = function(){
                var id = this.option.id;
                if (_.contains($scope.model, id)) {
                    $scope.model = _.without($scope.model, id);
                } else {
                    $scope.model.push(id);
                }
                console.log($scope.model);
                return false;
            };
            $scope.isChecked = function (id) {                 
                if (_.contains($scope.model, id)) {
                    return 'icon-ok pull-right';
                }
                return false;
            };                                 
       }
   } 
});

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
<link href="http://netdna.bootstrapcdn.com/twitter-bootstrap/2.3.0/css/bootstrap-combined.min.css" rel="stylesheet"/>
<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/3.10.1/lodash.js"></script>
<link href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/css/bootstrap.min.css" rel="stylesheet"/>
<script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.5/js/bootstrap.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<div ng-app="myApp" ng-controller="AppCtrl">        
  
   <dropdown-multiselect pre-selected="member.roles" model="selected_items" testElem = "dummyData" options="roles"></dropdown-multiselect>

在指令定义中的模板中，我有这一行：

<button class='btn btn-small'>{{$scope.testElem}}</button>

正如您在此行的帮助下所看到的，我尝试在 $ scope.testElem 变量中显示文本。

但文字没有出现。我错过了什么？为什么我在声明的按钮上看不到文字？

提前谢谢。