IObjectSpaceAsync.FindObjectAsync<ObjectType>(CriteriaOperator, CancellationToken) Method

Asynchronously searches for an object that matches the specified criteria. The specified generic parameter determines the object’s type.

Namespace: DevExpress.ExpressApp

Assembly: DevExpress.ExpressApp.v24.1.dll

NuGet Package: DevExpress.ExpressApp

Declaration

C#

Task<ObjectType> FindObjectAsync<ObjectType>(
    CriteriaOperator criteria,
    CancellationToken cancellationToken = default(CancellationToken)
)

VB.NET

Function FindObjectAsync(Of ObjectType)(
    criteria As CriteriaOperator,
    cancellationToken As CancellationToken = Nothing
) As Task(Of ObjectType)

Parameters

Name	Type	Description
criteria	CriteriaOperator	A CriteriaOperator descendant which represents the criteria the persistent object must match.

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
ObjectType	A type of objects to search for.

Returns

Type	Description
Task<ObjectType>	A Task that returns an object. This object represents a persistent object that matches the specified criteria. null (Nothing in Visual Basic) if no persistent object is found that matches the criteria.

Remarks

The following code demonstrates how you can use this method in a View Controller to find and show a Contact the selected DemoTask is assigned to. If this DemoTask is not assigned to any Contact, a Detail View for a new Contact object is shown.

C#

using DevExpress.Data.Filtering;
using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Actions;
using DevExpress.ExpressApp.Xpo;
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 assignedTo = (Contact)ViewCurrentObject.AssignedTo;
            if (assignedTo != null) {
                object obj = await contactObjectSpace.FindObjectAsync<Contact>(
                    CriteriaOperator.Parse(string.Format("[Oid] = '{0}'", assignedTo.Oid)), 
                    cancellationTokenSource.Token);
                contactView.CurrentObject = obj ?? contactObjectSpace.CreateObject(typeof(Contact));
            }
            else {
                contactView.CurrentObject = contactObjectSpace.CreateObject(typeof(Contact));
            }
        if (contactObjectSpace.IsNewObject(contactView.CurrentObject)) {
            contactObjectSpace.Committed += contactObjectSpace_Committed;
        }
    }
    private void contactObjectSpace_Committed(object sender, EventArgs e) {
        ViewCurrentObject.AssignedTo = ObjectSpace.GetObject(contactView.CurrentObject) as Contact;
    }
}

VB.NET

Imports DevExpress.Data.Filtering
Imports DevExpress.ExpressApp
Imports DevExpress.ExpressApp.Actions
Imports DevExpress.ExpressApp.Xpo
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 assignedTo As Contact = CType(ViewCurrentObject.AssignedTo, Contact)
        If assignedTo IsNot Nothing Then
            Dim obj As Object = Await contactObjectSpace.FindObjectAsync(Of Contact)( _
                CriteriaOperator.Parse(String.Format("[Oid] = '{0}'", assignedTo.Oid)),
                cancellationTokenSource.Token)
            contactView.CurrentObject = If(obj, contactObjectSpace.CreateObject(GetType(Contact)))
        Else
            contactView.CurrentObject = contactObjectSpace.CreateObject(GetType(Contact))
        End If
        If contactObjectSpace.IsNewObject(contactView.CurrentObject) Then
            AddHandler contactObjectSpace.Committed, AddressOf contactObjectSpace_Committed
        End If
    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.