AsyncCompletedEventArgs.UserState Property

public:
 property System::Object ^ UserState { System::Object ^ get(); };

public object UserState { get; }

public object? UserState { get; }

member this.UserState : obj

Public ReadOnly Property UserState As Object

Property Value

An object reference that uniquely identifies the asynchronous task; otherwise, null if no value has been set.

Examples

The following code example demonstrates using an AsyncOperation to track the lifetime of asynchronous operations. This code example is part of a larger example provided for the System.ComponentModel.AsyncOperationManager class.

using System;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Drawing;
using System.Globalization;
using System.Threading;
using System.Windows.Forms;

Imports System.Collections
Imports System.Collections.Specialized
Imports System.ComponentModel
Imports System.Drawing
Imports System.Globalization
Imports System.Threading
Imports System.Windows.Forms

// This event handler updates the ListView control when the
// PrimeNumberCalculator raises the CalculatePrimeCompleted
// event. The ListView item is updated with the appropriate
// outcome of the calculation: Canceled, Error, or result.
void primeNumberCalculator1_CalculatePrimeCompleted(
 object sender,
 CalculatePrimeCompletedEventArgs e)
{
 Guid taskId = (Guid)e.UserState;

 if (e.Cancelled)
 {
 string result = "Canceled";

 ListViewItem lvi = UpdateListViewItem(taskId, result);

 if (lvi != null)
 {
 lvi.BackColor = Color.Pink;
 lvi.Tag = null;
 }
 }
 else if (e.Error != null)
 {
 string result = "Error";

 ListViewItem lvi = UpdateListViewItem(taskId, result);

 if (lvi != null)
 {
 lvi.BackColor = Color.Red;
 lvi.ForeColor = Color.White;
 lvi.Tag = null;
 }
 }
 else
 {
 bool result = e.IsPrime;

 ListViewItem lvi = UpdateListViewItem(
 taskId,
 result,
 e.FirstDivisor);

 if (lvi != null)
 {
 lvi.BackColor = Color.LightGray;
 lvi.Tag = null;
 }
 }
}

' This event handler updates the ListView control when the
' PrimeNumberCalculator raises the CalculatePrimeCompleted
' event. The ListView item is updated with the appropriate
' outcome of the calculation: Canceled, Error, or result.
Private Sub primeNumberCalculator1_CalculatePrimeCompleted( _
 ByVal sender As Object, _
 ByVal e As CalculatePrimeCompletedEventArgs) _
 Handles primeNumberCalculator1.CalculatePrimeCompleted

 Dim taskId As Guid = CType(e.UserState, Guid)

 If e.Cancelled Then
 Dim result As String = "Canceled"

 Dim lvi As ListViewItem = UpdateListViewItem( _
 taskId, _
 result)

 If (lvi IsNot Nothing) Then
 lvi.BackColor = Color.Pink
 lvi.Tag = Nothing
 End If

 ElseIf e.Error IsNot Nothing Then

 Dim result As String = "Error"

 Dim lvi As ListViewItem = UpdateListViewItem( _
 taskId, result)

 If (lvi IsNot Nothing) Then
 lvi.BackColor = Color.Red
 lvi.ForeColor = Color.White
 lvi.Tag = Nothing
 End If
 Else
 Dim result As Boolean = e.IsPrime

 Dim lvi As ListViewItem = UpdateListViewItem( _
 taskId, _
 result, _
 e.FirstDivisor)

 If (lvi IsNot Nothing) Then
 lvi.BackColor = Color.LightGray
 lvi.Tag = Nothing
 End If
 End If

End Sub

Remarks

If a class supports multiple asynchronous methods, or multiple invocations of a single method, you can determine which task raised the MethodNameCompleted event by checking the value of the UserState property. Your code will need track these tokens, known as task IDs, as their corresponding asynchronous tasks start and complete.

The value of this property is set during the original call to the asynchronous method that started the task.

See also

• AsyncCompletedEventHandler
• AsyncOperationManager
• AsyncOperation
• Implementing the Event-based Asynchronous Pattern