Help Solving: Does not contain a definition for 'Select'.....

Hi,

Need help solving a Task that returns a Task<IEnumerable<Writing>> so I can fill ObservableCollection<ViewModels.IWritingItemViewModel> Writings for my Design Time Data Page:

<d:Page.DataContext>
        <designTimeData:MainPageViewModel />
</d:Page.DataContext>

My constructor does this:

public MainPageViewModel()
{
        var writings = this.GetGroupsAsync();
        this.Writings = new ObservableCollection<ViewModels.IWritingItemViewModel>();

        var viewmodels = writings.Select((x, i) => new WritingItemViewModel
        {
                Writing = x,
                VariableItemSize = (i == 0) ? Common.VariableItemSizes.Writings : Common.VariableItemSizes.Normal,
        });
}

My var writings = this.GetGroupsAsync(); is:

public async Task<IEnumerable<Writing>> GetGroupsAsync()
{
        await this.GetMenuDataAsync();

        return this.Groups;
}

which in turn gets data from:

private async Task GetMenuDataAsync()
{
        Uri dataUri = new Uri("ms-appx:///DesignTimeData/MenuData.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();
                Writing group = new Writing(
                        groupObject["UniqueId"].GetString(),
                        groupObject["IsHeaderInteractive"].GetBoolean(),
                        groupObject["ViewType"].GetString(),
                        groupObject["ModelType"].GetString(),
                        groupObject["Page"].GetString(),
                        groupObject["Title"].GetString(),
                        groupObject["Subtitle"].GetString(),
                        groupObject["ImagePath"].GetString(),
                        groupObject["Description"].GetString(),
                        groupObject["GroupId"].GetString()
                        );

                foreach (JsonValue itemValue in groupObject["WritingMenus"].GetArray())
                {
                        JsonObject itemObject = itemValue.GetObject();
                        group.WritingMenus.Add(new WritingMenu(
                                itemObject["UniqueId"].GetString(),
                                itemObject["Page"].GetString(),
                                itemObject["Title"].GetString(),
                                itemObject["Subtitle"].GetString(),
                                itemObject["ImagePath"].GetString(),
                                itemObject["Description"].GetString(),
                                itemObject["Content"].GetString(),
                                itemObject["WritingsId"].GetString(),
                                itemObject["GroupId"].GetString(),
                                Convert.ToInt32(itemObject["Item"].ValueType)
                                ));
                }
                this.Groups.Add(group);
        }
}

and I get this Error:

Error 5 'System.Threading.Tasks.Task<System.Collections.Generic.IEnumerable<App1.DesignTimeData.Writing>>' 
  does not contain a definition for 'Select' and no extension method 'Select' accepting a first argument of type 
  'System.Threading.Tasks.Task<System.Collections.Generic.IEnumerable<App1.DesignTimeData.Writing>>' 
  could be found (are you missing a using directive or an assembly reference?)

I'm creating collections of:

public interface IWritingItemViewModel : Common.IVariableSizedItem
{
        Models.Writing Writing { get; set; }
}

and my class for creating data is:

public class Writing
{
        public Writing(
        string uniqueId,
        bool isHeaderInteractive,
        string templateType,
        string viewModelType,
        string page,
        string title,
        string subtitle,
        string imagePath,
        string description,
        string groupId
                )
        {
                this.UniqueId = uniqueId;
                this.IsHeaderInteractive = isHeaderInteractive;
                this.TemplateType = templateType;
                this.ViewModelType = viewModelType;
                this.Page = page;
                this.Title = title;
                this.Subtitle = subtitle;
                this.ImagePath = imagePath;
                this.Description = description;
                this.GroupId = groupId;
                this.WritingMenus = new ObservableCollection<WritingMenu>();
        }

        public string UniqueId { get; private set; }
        public bool IsHeaderInteractive { get; private set; }
        public string TemplateType { get; private set; }
        public string ViewModelType { get; private set; }
        public string Page { get; private set; }
        public string Title { get; private set; }
        public string Subtitle { get; private set; }
        public string ImagePath { get; private set; }
        public string Description { get; private set; }
        public string GroupId { get; private set; }

        public virtual ObservableCollection<WritingMenu> WritingMenus { get; private set; }
}

How can I solve or successfully complete this code?

Thanks!...

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