javascript - .then angularjs 中的函数无法识别参数

Question

我想要实现的是一个生成 lisof 元类别的下拉列表。一旦用户选择元类别，参数应传递到 $scope.meta().then(...) 中存在的函数的 URI。但是，我传递的参数是类别； ng-model=“类别”。此参数未发送到 URI，我收到错误:

TypeError: Cannot read property 'category' of undefined

HTML:

 </select></center >
<center> <select ng-model="category"  > <!-- This produces drop down list from which the users selects a category which should then get passed to the meta1() function as a parameter to produce a further list for the drop down after that-->
<option size=50 value="" selected>Select a meta category</option>
 <option ng-repeat="meta in metas.metas" value="{{meta}}">{{meta}} </option>

</select></center>
<center> <select ng-model="category"  >
<option size=50 value="" disabled selected>Select a category</option>
 <option ng-repeat="category in categories.categories" value="{{category}}">{{category}} </option>

 </select></center>

Angular :

myApp.config(['$routeProvider', function($routeProvider) {
$routeProvider.when('/post', {
    templateUrl: 'templates/post.html',
    controller: 'PostCtrl'
})
}])
.controller('UserListCtrl', function ($scope, $http) {
$scope.list = function () { // this gets the list of places which works completely fine.
    $http.get('http://94.125.132.253:8001/getuncategorisedplaces').success(function (data) {

        $scope.places = data;
        console.log(data);
        $scope.message = 'List of Uncategorised places';
        $scope.meta = function () { // this gets list of meta categories, which is working fine.
            return $http.get('http://94.125.132.253:8000/getmetas').success(function (data) {

                $scope.metas = data;
                console.log(data);
                $scope.message = 'List of Uncategorised places';
            })
        }

//下面的函数应该从 HTML 中选择的上一个函数中获取参数类别。一旦发生这种情况，参数类别应作为 formdata.category(如下)传递，它将获取类别列表。

        $scope.meta().then(function (data) {
            var formdata = {
                'category': this.category,
            }
            var inserturl = 'http://94.125.132.253:8000/getcategories?meta=' + formdata.category;
            $http.get(inserturl).success(function (data) {

                $scope.categories = data;
                console.log(formdata.category);
                console.log(data);
                $scope.message = 'List of Uncategorised places';
            });


        });
    })
}
$scope.list();

Answer 1

我认为错误是由以下原因引起的:

$scope.meta().then(function meta1($scope,$http) {

因为元方法没有返回 promise 。如果您这样做，元方法可能会返回一个 promise :

$scope.meta= function(){
  return $http.get('http://94.125.132.253:8000/getmetas').success(function (data) {
    $scope.metas = data;
    console.log(data);
    $scope.message = 'List of Uncategorised places';
    return data;
  });
};

您可以将对元的调用更改为此

$scope.meta().then(function(data) {
...
}