IObjectSpaceAsync.PreFetchAsync(Object, String[], CancellationToken) Method

Asynchronously forces associated collection data loading and delayed property loading for specified parent objects.

Namespace: DevExpress.ExpressApp

Assembly: DevExpress.ExpressApp.v19.2.dll

Declaration

C#

Task PreFetchAsync(
    object collection,
    string[] propertyNames,
    CancellationToken cancellationToken = default(CancellationToken)
)

VB.NET

Function PreFetchAsync(
    collection As Object,
    propertyNames As String(),
    cancellationToken As CancellationToken = Nothing
) As Task

Parameters

Name	Type	Description
collection	Object	A collection of parent objects.
propertyNames	String[]	An array of strings that are the names of the associated collection properties or delayed properties.

Optional Parameters

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

Returns

Type	Description
Task	A Task object.

Remarks

The following code demonstrates how you can use this method in a WinForms-specific View Controller.

C#

using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Actions;
using DevExpress.ExpressApp.Xpo;
using MainDemo.Module.BusinessObjects;
using System;
using System.Threading;
// ...
public class AsyncAssignedToInfoController : ObjectViewController<ListView, DemoTask> {
    View contactView = null;
    public AsyncAssignedToInfoController() : base() {
        SimpleAction showAssignedToInfoAction = new SimpleAction(this, "Assigned contact's info", "Edit");
        showAssignedToInfoAction.SelectionDependencyType = SelectionDependencyType.RequireSingleObject;
        showAssignedToInfoAction.Execute += showAssignedToInfoAction_Execute;
    }
    async private void showAssignedToInfoAction_Execute(object sender, SimpleActionExecuteEventArgs e) {
        CancellationTokenSource cancellationTokenSource = new CancellationTokenSource();
        XPObjectSpace contactObjectSpace = (XPObjectSpace)Application.CreateObjectSpace(typeof(Contact));
        contactView = Application.CreateDetailView(contactObjectSpace, "Contact_DetailView", true);
        e.ShowViewParameters.CreatedView = contactView;
        Contact obj = null;
        if (ViewCurrentObject.AssignedTo != null) {
            obj = (Contact)await contactObjectSpace.GetObjectAsync(ViewCurrentObject.AssignedTo);
            Contact[] contacts = new Contact[] { obj };
            await contactObjectSpace.PreFetchAsync(contacts, new string[] { "Tasks" });
        }
        if (obj == null) {
            obj = contactObjectSpace.CreateObject<Contact>();
            contactObjectSpace.Committed += contactObjectSpace_Committed;
        }
        contactView.CurrentObject = obj;
    }
    private void contactObjectSpace_Committed(object sender, EventArgs e) {
        ViewCurrentObject.AssignedTo = ObjectSpace.GetObject(contactView.CurrentObject) as Contact;
    }
}

VB.NET

Imports DevExpress.ExpressApp
Imports DevExpress.ExpressApp.Actions
Imports DevExpress.ExpressApp.Xpo
Imports MainDemo.Module.BusinessObjects
Imports System
Imports System.Threading
' ...
Public Class AsyncAssignedToInfoController
    Inherits ObjectViewController(Of ListView, DemoTask)
    Private contactView As View = Nothing
    Public Sub New()
        MyBase.New()
        Dim showAssignedToInfoAction As New SimpleAction(Me, "Assigned contact's info", "Edit")
        showAssignedToInfoAction.SelectionDependencyType = SelectionDependencyType.RequireSingleObject
        AddHandler showAssignedToInfoAction.Execute, AddressOf showAssignedToInfoAction_Execute
    End Sub
    Private Async Sub showAssignedToInfoAction_Execute(ByVal sender As Object, ByVal e As SimpleActionExecuteEventArgs)
        Dim cancellationTokenSource As New CancellationTokenSource()
        Dim contactObjectSpace As XPObjectSpace = CType(Application.CreateObjectSpace(GetType(Contact)), XPObjectSpace)
        contactView = Application.CreateDetailView(contactObjectSpace, "Contact_DetailView", True)
        e.ShowViewParameters.CreatedView = contactView
        Dim obj As Contact = Nothing
        If ViewCurrentObject.AssignedTo IsNot Nothing Then
            obj = CType(Await contactObjectSpace.GetObjectAsync(ViewCurrentObject.AssignedTo), Contact)
            Dim contacts() As Contact = {obj}
            Await contactObjectSpace.PreFetchAsync(contacts, New String() {"Tasks"})
        End If
        If obj Is Nothing Then
            obj = contactObjectSpace.CreateObject(Of Contact)()
            AddHandler contactObjectSpace.Committed, AddressOf contactObjectSpace_Committed
        End If
        contactView.CurrentObject = obj
    End Sub
    Private Sub contactObjectSpace_Committed(ByVal sender As Object, ByVal e As EventArgs)
        ViewCurrentObject.AssignedTo = TryCast(ObjectSpace.GetObject(contactView.CurrentObject), Contact)
    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.