Async gridview and waiting bar

[Martin]

Hi Folks,

I have an Async Task which uses a LINQ query to fetch rows of data.

public async Task<List<POMastObject>> FetchPOMastsAsync()
        {
            try
            {
                using (var db = new DBContext())
                {
                    return await (from p in db.POMasts.AsNoTracking()
                            join pr in db.Profiles.AsNoTracking() on p.ProfileID equals pr.ID
                            join c in db.CurrencyTypes.AsNoTracking() on p.CurrencyTypeID equals c.ID
                            join w in db.WHMasts.AsNoTracking() on p.WarehouseID equals w.ID
                            join t in db.TermCodeTypes.AsNoTracking() on p.TermCodeTypeID equals t.ID
                            join s in db.POMastStatusTypes.AsNoTracking() on p.StatusID equals s.ID

                            //Ensure that these are dynamic
                            where (_viewfetch.VendMastID == -1 || p.VendorID == _viewfetch.VendMastID) &&
                            (_viewfetch.POMastStatusID == -1 || p.StatusID == _viewfetch.POMastStatusID)

                            orderby p.ID

                            //Put the query results into the bespoke object
                            select new POMastObject
                            {
                                ID = p.ID,
                                OrderNo = p.OrderNo,
                                RaisedDate = p.RaisedDate,
                                RaisedBy = pr.Name,
                                Currency = c.Description,
                                Warehouse = w.Description,
                                Terms = t.Description,
                                LastEditedBy = p.LastEditedBy,
                                LastEditedDate = p.LastEditedDate,
                                Status = s.Name
                            }).ToListAsync();
                }
            }

Which is consumed on the form as follows:

private async void GetSearchResultVendorAsync()
        {
            try
            {              
                radGridViewResult.DataSource = await _poasync.FetchPOMastsAsync();
                radGroupBoxResult.FooterText = "Search Results (" + radGridViewResult.RowCount.ToString() + " Records)";
            }
            catch (Exception ex)
            {
                GlobalErrorHandler.CallingRoutine = MethodBase.GetCurrentMethod().Name;
                GlobalErrorHandler.CallingModule = typeof(frmSearchPO).ToString();
                GlobalErrorHandler.Exception = ex.Message.ToString();
                GlobalErrorHandler.HandleError();
            }
        }

I am trying to have a radWaitngBar wrapped around this to StartWaiting and StopWaiting but so far have been unable to get it to work

I tried the following:

private async void radButtonSearch_Click(object sender, EventArgs e)
        {
            try
            {
                InitMemberVars();
                radWaitingBar1.StartWaiting();

                await Task.Run(() =>
                {
                    GetSearchResultVendorAsync();
                });
                radWaitingBar1.StopWaiting();
            }

Which starts the animation but then falls over with a System.NullReferenceeException in Telerik,WinControls.dll

If I don't use radWaitingBar the grid is populated correctly, and you are still able to drag the radForm around the screen whilst the async data fetch is running.

Any ideas folks?

Thanks

Martin.

[Martin]

It was solved by altering the code (on the form) that consumes the Task. Thought it may be handy for anyone else doing something similar. The code goes into an async void routine (such as private async void radButtonSearch_Click):

radWaitingBarResult.Visible = true;
radWaitingBarResult.StartWaiting();

var result = await _poasync.FetchPOMastsAsync();
                if (!Equals(result,null))   //<<== This code will not execute till the await finishes
                    radGridViewResult.DataSource = result;

radWaitingBarResult.StopWaiting();
radWaitingBarResult.Visible = false;

[Hristo]

Hello Martin,

Thank you for writing.

I am glad that you managed to find a solution which fits your scenario. Thank you also for sharing it with the community. In case you need additional information or further assistance just let me know.

Should you have further questions please do not hesitate to write back.

Regards,
Hristo Merdjanov
Telerik