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AsyncCompletedEventArgs.UserState Property

Gets the unique identifier for the asynchronous task.

Namespace: System.ComponentModel
Assembly: System (in system.dll)

'Declaration
Public ReadOnly Property UserState As Object
'Usage
Dim instance As AsyncCompletedEventArgs
Dim value As Object

value = instance.UserState

/** @property */
public Object get_UserState ()

public function get UserState () : Object

Not applicable.

Property Value

An object reference that uniquely identifies the asynchronous task; otherwise, a null reference (Nothing in Visual Basic) if no value has been set.

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.

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.

Imports System
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.
    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

import System.*;
import System.Collections.*;
import System.Collections.Specialized.*;
import System.ComponentModel.*;
import System.Data.*;
import System.Drawing.*;
import System.Threading.*;
import System.Windows.Forms.*;


	...

    private void primeNumberCalculator1_CalculatePrimeCompleted(Object sender,
        CalculatePrimeCompletedEventArgs e)
    {
        Guid guid = (Guid)e.get_UserState();
        if (e.get_Cancelled()) {
            String result = "Cancelled";
            ListViewItem lvi = UpdateListViewItem((Guid)e.get_UserState(),
                result);
            if (lvi != null) {
                lvi.set_BackColor(Color.get_Pink());
                lvi.set_Tag(null);
            }
        }
        else {
            if (e.get_Error() != null) {
                String result = "Error";
                ListViewItem lvi = UpdateListViewItem((Guid)e.get_UserState(),
                    result);
                if (lvi != null) {
                    lvi.set_BackColor(Color.get_Red());
                    lvi.set_ForeColor(Color.get_White());
                    lvi.set_Tag(null);
                }
            }
            else {
                boolean result = e.get_IsPrime();
                ListViewItem lvi = UpdateListViewItem((Guid)e.get_UserState(),
                    result, e.get_FirstDivisor());
                if (lvi != null) {
                    lvi.set_BackColor(Color.get_LightGray());
                    lvi.set_Tag(null);
                }
            }
        }
    } //primeNumberCalculator1_CalculatePrimeCompleted

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0

XNA Framework

Supported in: 1.0

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