Async On Demand Loading

[Frido Dombek]

Hi,I have to load data asynchronously from the web and want to display it in a SfTreeGrid using 'On Demand Loading'. 

However I couldn't figure out a way to populate the tree on demand when I'm calling and awaiting async functions to load the data.

As an example, if modify your OnDemandLoading Example and add a await Task.Delay(1) call to the code, it won't populate the tree with tree nodes anymore.

/// <summary>
/// Gets the reportees.
/// </summary>
/// <param name="bossID">The boss ID.</param>
/// <returns></returns>
public async Task<IEnumerable<EmployeeInfo>> GetReportees(int bossID)
{
 
    List<EmployeeInfo> list = new List<EmployeeInfo>();
    int loc = FindID(bossID);
    if (loc > -1)
    {
        await Task.Delay(1);
        while (loc < this.EmployeeDetails.Count && this.EmployeeDetails[loc].ReportsTo == bossID)
            list.Add(this.EmployeeDetails[loc++]);
    }
    return list;
}

I then await this function in:

async void AssociatedObject_RequestTreeItems(object sender, TreeGridRequestTreeItemsEventArgs args)

How can I populate the SfTreeGrid on demand with data that is loaded asynchronously?

Regards and Thanks,

Frido

[Muthukumar Kalyanasundaram]

Hi Frido, 

Thank you for contacting Syncfusion support. 

We have checked your query. We are able to reproduce the reported query in our end. You can overcome this problem by handling the AutoResetEvent. For your reference, we have attached the code snippet and sample in the below location, 

Code Snippet: 

 

System.Threading.AutoResetEvent autoreset = new System.Threading.AutoResetEvent(false); 

 

async void AssociatedObject_RequestTreeItems(object sender, TreeGridRequestTreeItemsEventArgs args) 

{ 

    if (args.ParentItem == null) 

    { 

        //get the root list - get all employees who have no boss  

        args.ChildItems = viewModel.EmployeeDetails.Where(x => x.ReportsTo == -1); //get all employees whose boss's id is -1 (no boss) 

    } 

    else //if ParentItem not null, then set args.ChildList to the child items for the given ParentItem. 

    {   //get the children of the parent object 

        EmployeeInfo emp = args.ParentItem as EmployeeInfo; 

        if (emp != null) 

        { 

            Task t = Task.Run(() => 

            { 

                GetChildItem(args); 

            }); 

            autoreset.WaitOne(); 

        } 

    } 

} 

 

private async void GetChildItem(TreeGridRequestTreeItemsEventArgs args) 

{ 

    EmployeeInfo emp = args.ParentItem as EmployeeInfo; 

    args.ChildItems = await viewModel.GetReportees(emp.ID); 

    autoreset.Set(); 

} 

Sample: https://www.syncfusion.com/downloads/support/forum/129665/ze/OnDemandLoadingDemo-372535235 

Please let us know if you have any query. 

Regards, 

Muthukumar K