public static async Task RefreshDataSource()
        {
            //var groupService = new GetData();
            var allGroups = await GetData.getMyDataAsync();
  
            foreach (var group in allGroups)
            {
                SampleDataGroup mySampleDataGroup = new SampleDataGroup(
                    group.CourseId.ToString(),
                    group.Title.ToString(),
                    group.Subtitle.ToString(),
                    group.ImagePath.ToString(),
                    group.Description.ToString()
                );

                _sampleDataSource._groups.Add(mySampleDataGroup);

                if (group.Attendants != null)
                {
                    foreach (var item in group.Attendants)
                    {
                        mySampleDataGroup.Items.Add(new SampleDataItem(
                            item.StudentId.ToString(),
                            item.Title,
                            item.Subtitle,
                            item.ImagePath,//"Assets/LightGray.png",
                            item.Description,
                            item.Content));
                    }
                }
            }

        }
        private async Task GetSampleDataAsync()
        {
            if (this._groups.Count != 0)
                return;

            Uri dataUri = new Uri("ms-appx:///DataModel/SampleData.json");

            StorageFile file = await StorageFile.GetFileFromApplicationUriAsync(dataUri);
            string jsonText = await FileIO.ReadTextAsync(file);
            JsonObject jsonObject = JsonObject.Parse(jsonText);
            JsonArray jsonArray = jsonObject["Groups"].GetArray();

            foreach (JsonValue groupValue in jsonArray)
            {
                JsonObject groupObject = groupValue.GetObject();
                SampleDataGroup group = new SampleDataGroup(groupObject["UniqueId"].GetString(),
                                                            groupObject["Title"].GetString(),
                                                            groupObject["Subtitle"].GetString(),
                                                            groupObject["ImagePath"].GetString(),
                                                            groupObject["Description"].GetString());

                foreach (JsonValue itemValue in groupObject["Items"].GetArray())
                {
                    JsonObject itemObject = itemValue.GetObject();
                    group.Items.Add(new SampleDataItem(itemObject["UniqueId"].GetString(),
                                                       itemObject["Title"].GetString(),
                                                       itemObject["Subtitle"].GetString(),
                                                       itemObject["ImagePath"].GetString(),
                                                       itemObject["Description"].GetString(),
                                                       itemObject["Content"].GetString()));
                }
                this.Groups.Add(group);
            }
        }