angular 监控表单是否被修改过

 $scope.phoneFeeModel.errorMessage=resultObject.errorMessage;
                $scope.phoneFeeForm.$setDirty(false);
                $scope.loginForm.$setPristine(true);
                var unWatch = $scope.$wath('phoneFeeForm.$dirty',function(){
                    if($scope.phoneFeeForm.$dirty){
                        $scope.phoneFeeForm.errorMessage='';
                        unWatch();
                    }
                })