private async Task GetDataAsync()
{
if (this._groups.Count != 0)
return;
var dataService = new DataService();
DataGroup group1 = await dataService.GetDataGroup1();
DataGroup group2 = await dataService.GetDataGroup2();
DataGroup videos = await dataService.GetDataGroupVideos();
DataGroup group4 = await dataService.GetDataGroup4();
this.Groups.Add(group4);//personel first.
this.Groups.Add(group1);
this.Groups.Add(group2);
Groups.Add(videos);
}