AngularJS-Bootstrap中的错误TypeAhead：TypeError：无法读取未定义的属性“length”

Question

我在尝试从AngularUI-Bootstrap实现AngularJS Typeahead时遇到以下错误： （我只是调用一个以JSON格式返回结果的servlet）

TypeError: Cannot read property 'length' of undefined
    at http://angular-ui.github.io/bootstrap/ui-bootstrap-tpls-0.11.0.js:3553:24
    at wrappedCallback (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular.js:10930:81)
    at wrappedCallback (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular.js:10930:81)
    at http://ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular.js:11016:26
    at Scope.$eval (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular.js:11936:28)
    at Scope.$digest (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular.js:11762:31)
    at Scope.$apply (http://ajax.googleapis.com/ajax/libs/angularjs/1.2.10/angular.js:12042:24)

HTML

<h4>Users from local service</h4>
    <pre>Model: {{userList | json}}</pre>
    <input type="text" ng-model="userList" placeholder="Users loaded from local database" 
    typeahead="username for username in fetchUsers($viewValue)" 
    typeahead-loading="loadingUsers" class="form-control">
    <i ng-show="loadingUsers" class="glyphicon glyphicon-refresh"></i>

JS

$scope.fetchUsers = function(val) {
        console.log("Entered fetchUsers function");
        $http.get("http://localhost:8080/TestWeb/users", {
            params : {
                username : val
            }
        }).then(function(res) {
            var users = [];
            angular.forEach(res.data, function(item) {
                users.push(item.UserName);
            });
            return users;
        });
    };

的Servlet

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        UserUtil userUtil = new UserUtil();
        List userList = userUtil.fetchUsers();
        Iterator userIterator = userList.iterator();

        JSONArray users = new JSONArray();


        while(userIterator.hasNext()) {
            UserDetails userDetails = (UserDetails)userIterator.next();

            JSONObject jo =  new JSONObject();
            jo.put("UserID", userDetails.getUserId());
            jo.put("UserName", userDetails.getUserName());
            jo.put("UserDescription", userDetails.getDescription());

            users.add(jo);
        }

        response.setContentType("application/json");
        response.getWriter().write(users.toString());


    }

来自servlet的响应

我已经提到了以下问题：

• AngularUI-Bootstrap's Typeahead Can't Read `length` Property of `undefined`
• typeahead angular ui - cannot read property 'length' of undefined

然而，我仍然无法弄清楚决议。 servlet本身的响应有什么问题吗？还是别的什么？

Answer 1

在第二次查看代码之后我已经注意到了什么错误，你必须在这里返回$ http promise，在$ http

之前注意return

$scope.fetchUsers = function(val) {
        console.log("Entered fetchUsers function");
        return $http.get("http://localhost:8080/TestWeb/users", {
            params : {
                username : val
            }
        }).then(function(res) {
            var users = [];
            angular.forEach(res.data, function(item) {
                users.push(item.UserName);
            });
            return users;
        });
    };