XPObjectSpace.ToListAsync<T>(Object, CancellationToken) Method

Asynchronously enumerates all elements in a collection and saves them to a list.

Namespace: DevExpress.ExpressApp.Xpo

Assembly: DevExpress.ExpressApp.Xpo.v19.2.dll

Declaration

C#

public Task<List<T>> ToListAsync<T>(
    object collection,
    CancellationToken cancellationToken = default(CancellationToken)
)

VB.NET

Public Function ToListAsync(Of T)(
    collection As Object,
    cancellationToken As CancellationToken = Nothing
) As Task(Of List(Of T))

Parameters

Name	Type	Description
collection	Object	A collection to be enumerated.

Optional Parameters

Name	Type	Default	Description
cancellationToken	CancellationToken	*null*	A CancellationToken object that delivers a cancellation notice to the running operation.

Type Parameters

Name	Description
T	The type of elements in the specified collection.

Returns

Type	Description
Task<List<T>>	A Task that returns a list of objects.

Remarks

Use the GetObjectsQuery<T>(Boolean) method to get the XPQuery<T> object to pass it as the ToListAsync<T>(Object, CancellationToken)‘s collection parameter. You can also create this object manually.

The following code demonstrates how you can use this method in a WinForms-specific View Controller to add contacts from the Development Department to the task’s Contacts collection.

C#

using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Actions;
using DevExpress.ExpressApp.Win;
using DevExpress.ExpressApp.Xpo;
using DevExpress.XtraSplashScreen;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Windows.Forms;
// ...
public class AsyncTaskContactsController : ObjectViewController<DetailView, DemoTask> {
    public AsyncTaskContactsController() : base() {
        base.OnActivated();
        SimpleAction assignToDepartmentAction = new SimpleAction(this, "Assign to the Dev.Departmant", "Edit");
        assignToDepartmentAction.SelectionDependencyType = SelectionDependencyType.RequireSingleObject;
        assignToDepartmentAction.Execute += assignToDepartmentAction_Execute;
    }
    async private void assignToDepartmentAction_Execute(object sender, SimpleActionExecuteEventArgs e) {
        IOverlaySplashScreenHandle handle = null;
        Control control = Frame.Template as Control;
        WinApplication application = Application as WinApplication;
        CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
        var contacts = from c in ObjectSpace.GetObjectsQuery<Contact>()
                        where c.Department.Title == "Development Department"
                        select c;
        IList<Contact> contactsList = null;
        try {
            if (control != null && control.IsHandleCreated) {
                handle = application.StartOverlayForm(control);
            }
            contactsList = await ((XPObjectSpace)ObjectSpace).ToListAsync<Contact>(contacts, cancellationTokenSource.Token);
            ViewCurrentObject.Contacts.AddRange(contactsList);
        }
        finally {
            if (handle != null) {
                application.StopOverlayForm(handle);
            }
        }
    }
}

VB.NET

Imports DevExpress.ExpressApp
Imports DevExpress.ExpressApp.Actions
Imports DevExpress.ExpressApp.Win
Imports DevExpress.ExpressApp.Xpo
Imports DevExpress.XtraSplashScreen
Imports System.Collections.Generic
Imports System.Threading
Imports System.Windows.Forms
' ...
Public Class AsyncTaskContactsController
    Inherits ObjectViewController(Of DetailView, DemoTask)
    Public Sub New()
        MyBase.New()
        MyBase.OnActivated()
        Dim assignToDepartmentAction As New SimpleAction(Me, "Assign to the Dev.Departmant", "Edit")
        assignToDepartmentAction.SelectionDependencyType = SelectionDependencyType.RequireSingleObject
        AddHandler assignToDepartmentAction.Execute, AddressOf assignToDepartmentAction_Execute
    End Sub
    Private Async Sub assignToDepartmentAction_Execute(ByVal sender As Object, ByVal e As SimpleActionExecuteEventArgs)
        Dim handle As IOverlaySplashScreenHandle = Nothing
        Dim control As Control = TryCast(Frame.Template, Control)
        Dim _application As WinApplication = TryCast(Application, WinApplication)
        Dim cancellationTokenSource As New CancellationTokenSource()
        Dim contacts As IQueryable(Of Contact) = From c In ObjectSpace.GetObjectsQuery(Of Contact)()
                                                 Where c.Department.Title = "Development Department"
                                                 Select c
        Dim contactsList As IList(Of Contact) = Nothing
        Try
            If control IsNot Nothing AndAlso control.IsHandleCreated Then
                handle = _application.StartOverlayForm(control)
            End If
            contactsList =
                Await CType(ObjectSpace, XPObjectSpace).ToListAsync(Of Contact)(contacts,
                cancellationTokenSource.Token)
            ViewCurrentObject.Contacts.AddRange(contactsList)
        Finally
            If handle IsNot Nothing Then
                _application.StopOverlayForm(handle)
            End If
        End Try
    End Sub
End Class

In the current example, the cancellationToken parameter is used for demonstration purposes. You can skip it or use to cancel an asynchronous operation as shown in the CancellationToken topic.

Implements

ToListAsync<T>(Object, CancellationToken)