angularjs - 在 AngularJS 自定义验证指令中调用异步服务

Question

我有一个自定义验证指令(验证用户名不存在)。验证使用 $http 服务询问服务器用户名是否存在，因此返回的是一个 promise 对象。这对于验证非常有用。该表单无效，并且在用户名已被使用时包含 myform.$error.usernameVerify。但是， user.username 始终未定义，因此它破坏了我的 ng-model 指令。我认为这可能是因为 .success 中的函数正在创建它自己的范围，并且 Controller $scope 上没有使用返回值。我该如何解决这个问题，以便 ng-model 绑定(bind)仍然有效？

commonModule.directive("usernameVerify", [
    'userSvc', function(userSvc) {
        return {
            require: 'ngModel',
            scope: false,
            link: function(scope, element, attrs, ctrl) {
                ctrl.$parsers.unshift(checkForAvailability);
                ctrl.$formatters.unshift(checkForAvailability);

                function checkForAvailability(value) {
                    if (value.length < 5) {
                        return value;
                    }
                    // the userSvc.userExists function is just a call to a rest api using $http
                    userSvc.userExists(value)
                        .success(function(alreadyUsed) {
                            var valid = alreadyUsed === 'false';
                            if (valid) {
                                ctrl.$setValidity('usernameVerify', true);
                                return value;
                            } 
                            ctrl.$setValidity('usernameVerify', false);
                            return undefined;
                        });
                }
            }
        }
    }
]);

这是我的模板:

<div class="form-group" ng-class="{'has-error': accountForm.username.$dirty && accountForm.username.$invalid}">
    <label class=" col-md-3 control-label">Username:</label>
    <div class="col-md-9">
        <input name="username"
               type="text"
               class="form-control"
               ng-model="user.username"
               ng-disabled="user.id"
               ng-minlength=5
               username-verify
               required />
        <span class="field-validation-error" ng-show="accountForm.username.$dirty && accountForm.username.$error.required">Username is required.</span>
        <span class="field-validation-error" ng-show="accountForm.username.$dirty && accountForm.username.$error.minlength">Username must be at least 5 characters.</span>
        <span class="field-validation-error" ng-show="accountForm.username.$dirty && accountForm.username.$error.usernameVerify">Username already taken.</span>
    </div>
</div>

Answer 1

对于这种情况，Angular 有一个专用的 $asyncValidators 数组:

见 https://docs.angularjs.org/api/ng/type/ngModel.NgModelController

ngModel.$asyncValidators.uniqueUsername = function(modelValue, viewValue) {
var value = modelValue || viewValue;

// Lookup user by username
return $http.get({url:'/api/users/' + value}).
   then(function resolved() {
     //username exists, this means validation fails
     return $q.reject('exists');
   }, function rejected() {
     //username does not exist, therefore this validation passes
     return true;
   });
};