AsyncCompletedEventArgs.UserState Properti

  • Referensi

Definisi

Ruang nama:
System.ComponentModel
Rakitan:
System.ComponentModel.EventBasedAsync.dll
Rakitan:
System.dll
Rakitan:
netstandard.dll
Sumber:
AsyncCompletedEvent.cs
Sumber:
AsyncCompletedEvent.cs
Sumber:
AsyncCompletedEvent.cs

Mendapatkan pengidentifikasi unik untuk tugas asinkron.

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

Nilai Properti

Object

Referensi objek yang secara unik mengidentifikasi tugas asinkron; jika tidak, null jika tidak ada nilai yang ditetapkan.

Contoh

Contoh kode berikut menunjukkan penggunaan AsyncOperation untuk melacak masa pakai operasi asinkron. Contoh kode ini adalah bagian dari contoh yang lebih besar yang disediakan untuk System.ComponentModel.AsyncOperationManager kelas .

using System;
using System.Collections;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Data;
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.
private 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

Keterangan

Jika kelas mendukung beberapa metode asinkron, atau beberapa pemanggilan satu metode, Anda dapat menentukan tugas mana yang menaikkan peristiwa MethodNameCompleted dengan memeriksa nilai UserState properti . Kode Anda akan perlu melacak token ini, yang dikenal sebagai ID tugas, saat tugas asinkron yang sesuai dimulai dan selesai.

Nilai properti ini diatur selama panggilan asli ke metode asinkron yang memulai tugas.

Berlaku untuk

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