事件概述

引入了 Control.InvokeAsync.NET 9，它为 UI 线程提供异步友好的封送处理。 与发送（阻止调用线程）不同Control.Invoke，将Control.InvokeAsync（非阻止）发布到 UI 线程的消息队列。 有关详细信息 Control.InvokeAsync，请参阅 如何对控件进行线程安全的调用。

InvokeAsync 的主要优势：

• 非阻塞：立即返回，允许调用线程继续。
• 异步友好：返回可以等待的项 Task 。
• 异常传播：正确将异常传播回调用代码。
• 取消支持：支持 CancellationToken 作取消。

private async void processButton_Click(object sender, EventArgs e)
{
    processButton.Enabled = false;
    
    // Start background work
    await Task.Run(async () =>
    {
        for (int i = 0; i <= 100; i += 10)
        {
            // Simulate work
            await Task.Delay(200);
            
            // Create local variable to avoid closure issues
            int currentProgress = i;
            
            // Update UI safely from background thread
            await progressBar.InvokeAsync(() =>
            {
                progressBar.Value = currentProgress;
                statusLabel.Text = $"Progress: {currentProgress}%";
            });
        }
    });
    
    processButton.Enabled = true;
}

Private Async Sub processButton_Click(sender As Object, e As EventArgs) Handles processButton.Click
    processButton.Enabled = False

    ' Start background work
    Await Task.Run(Async Function()
                       For i As Integer = 0 To 100 Step 10
                           ' Simulate work
                           Await Task.Delay(200)

                           ' Create local variable to avoid closure issues
                           Dim currentProgress As Integer = i

                           ' Update UI safely from background thread
                           Await progressBar.InvokeAsync(Sub()
                                                             progressBar.Value = currentProgress
                                                             statusLabel.Text = $"Progress: {currentProgress}%"
                                                         End Sub)
                       Next
                   End Function)

    processButton.Enabled = True
End Sub

对于需要在 UI 线程上运行的真正异步作：

private async void complexButton_Click(object sender, EventArgs e)
{
    // This runs on UI thread but doesn't block it
    statusLabel.Text = "Starting complex operation...";

    // Dispatch and run on a new thread
    await Task.WhenAll(Task.Run(SomeApiCallAsync),
                       Task.Run(SomeApiCallAsync),
                       Task.Run(SomeApiCallAsync));

    // Update UI directly since we're already on UI thread
    statusLabel.Text = "Operation completed";
}

private async Task SomeApiCallAsync()
{
    using var client = new HttpClient();

    // Simulate random network delay
    await Task.Delay(Random.Shared.Next(500, 2500));

    // Do I/O asynchronously
    string result = await client.GetStringAsync("https://github.com/dotnet/docs/raw/refs/heads/main/README.md");

    // Marshal back to UI thread
    await this.InvokeAsync(async (cancelToken) =>
    {
        loggingTextBox.Text += $"{Environment.NewLine}Operation finished at: {DateTime.Now:HH:mm:ss.fff}";
    });

    // Do more async I/O ...
}

Private Async Sub complexButton_Click(sender As Object, e As EventArgs) Handles complexButton.Click
    'Convert the method to enable the extension method on the type
    Dim method = DirectCast(AddressOf ComplexButtonClickLogic,
                            Func(Of CancellationToken, Task))

    'Invoke the method asynchronously on the UI thread
    Await Me.InvokeAsync(method.AsValueTask())
End Sub

Private Async Function ComplexButtonClickLogic(token As CancellationToken) As Task
    ' This runs on UI thread but doesn't block it
    statusLabel.Text = "Starting complex operation..."

    ' Dispatch and run on a new thread
    Await Task.WhenAll(Task.Run(AddressOf SomeApiCallAsync),
                       Task.Run(AddressOf SomeApiCallAsync),
                       Task.Run(AddressOf SomeApiCallAsync))

    ' Update UI directly since we're already on UI thread
    statusLabel.Text = "Operation completed"
End Function

Private Async Function SomeApiCallAsync() As Task
    Using client As New HttpClient()

        ' Simulate random network delay
        Await Task.Delay(Random.Shared.Next(500, 2500))

        ' Do I/O asynchronously
        Dim result As String = Await client.GetStringAsync("https://github.com/dotnet/docs/raw/refs/heads/main/README.md")

        ' Marshal back to UI thread
        ' Extra work here in VB to handle ValueTask conversion
        Await Me.InvokeAsync(DirectCast(
                Async Function(cancelToken As CancellationToken) As Task
                    loggingTextBox.Text &= $"{Environment.NewLine}Operation finished at: {DateTime.Now:HH:mm:ss.fff}"
                End Function,
            Func(Of CancellationToken, Task)).AsValueTask() 'Extension method to convert Task
        )

        ' Do more Async I/O ...
    End Using
End Function

对于面向 .NET Framework 的应用程序，请使用具有适当异步处理的传统模式：

private async void legacyButton_Click(object sender, EventArgs e)
{
    var legacyButton = sender as Button;
    legacyButton.Enabled = false;
    
    try
    {
        // Move to background thread to avoid blocking UI
        await Task.Run(async () =>
        {
            var result = await SomeAsyncOperation();
            
            // Marshal back to UI thread
            this.Invoke(new Action(() =>
            {
                loggingTextBox.Text = result;
                statusLabel.Text = "Complete";
            }));
        });
    }
    finally
    {
        // This runs on the UI thread since the await completed
        legacyButton.Enabled = true;
    }
}

private async Task<string> SomeAsyncOperation()
{
    using var httpClient = new HttpClient();
    await Task.Delay(2000); // Simulate delay
    return await httpClient.GetStringAsync("https://github.com/dotnet/docs/raw/refs/heads/main/README.md");
}

Private Async Sub legacyButton_Click(sender As Object, e As EventArgs) Handles legacyButton.Click
    Dim legacyButton As Button = TryCast(sender, Button)
    legacyButton.Enabled = False

    Try
        ' Move to background thread to avoid blocking UI
        Await Task.Run(Async Function()
                           Dim result As String = Await SomeAsyncOperation()

                           ' Marshal back to UI thread
                           Me.Invoke(New Action(Sub()
                                                    loggingTextBox.Text = result
                                                    statusLabel.Text = "Complete"
                                                End Sub))
                       End Function)
    Finally
        ' This runs on the UI thread since the await completed
        legacyButton.Enabled = True
    End Try
End Sub

Private Async Function SomeAsyncOperation() As Task(Of String)
    Using httpClient As New HttpClient()
        Return Await httpClient.GetStringAsync("https://github.com/dotnet/docs/raw/refs/heads/main/README.md")
    End Using
End Function