Rebex Graph

.NET client library for MS Graph API (Exchange Online)

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Asynchronous operations

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Task-based Asynchronous Pattern (.NET 4.0 or later) 

.NET 4.0 introduced the Task-based Asynchronous Pattern (TAP). Rebex Graph supports it as well - just reference the assemblies for .NET 4.0 from your project. 

// create Graph client instance, connect, log in
// ...

// start async operation
Task<MailMessage> t = client.GetMailMessageAsync(messageId);

// set continuation method
t.ContinueWith(GetMailMessageFinished);

' create client instance, connect, log in
' ...

' start async operation
Dim t As Task(Of MailMessage) = client.GetMailMessageAsync(messageId)

' set continuation method
t.ContinueWith(AddressOf GetMessageListFinished)

Sample asynchronous continuation method:

// this method is called when the async operation is completed
private void GetMailMessageFinished(Task<MailMessage> t)
{
    // show error if any
    if (t.IsFaulted)
    {
        Console.WriteLine("An error occurred: {0}", t.Exception.ToString());
        return;
    }

    // show cancel notification
    if (t.IsCanceled)
    {
        Console.WriteLine("Operation was canceled.");
        return;
    }

    // get operation result
    MailMessage mail = t.Result;

    // show result
    Console.WriteLine("Mail downloaded: {0}", mail.Subject);
}

' this method is called when the async operation is completed
Private Sub GetMessageListFinished(t As Task(Of MailMessage))
    ' show error if any
    If t.IsFaulted Then
        Console.WriteLine("An error occurred: {0}", t.Exception.ToString())
        Return
    End If

    ' show cancel notification
    If t.IsCanceled Then
        Console.WriteLine("Operation was canceled.")
        Return
    End If

    ' get operation result
    Dim mail As MailMessage = t.Result

    ' show result
    Console.WriteLine("Mail downloaded: {0}", mail.Subject)
End Sub

'await' operator support (.NET 4.5 or later) 

.NET 4.5 introduced the 'await' operator, which makes writing asynchronous code more easy than ever before. Rebex Mail Pack supports it as well, just reference the assemblies for .NET 4.0 from your project. 

// create Graph client instance, connect, log in
// ...

try
{
    // download message asynchronously
    MailMessage mail = await client.GetMailMessageAsync(messageId);

    // show result
    Console.WriteLine("Mail downloaded: {0}", mail.Subject);
}
catch (GraphException ex)
{
    Console.WriteLine("An error occurred: {0}.", ex.Message);
}
catch (Exception ex)
{
    Console.WriteLine("An error occurred: {0}", ex.ToString());
}

' create Graph client instance, connect, log in
' ...
Try
    ' download message asynchronously
    Dim mail = Await client.GetMailMessageAsync(messageId)

    ' show result
    Console.WriteLine("Mail downloaded: {0}", mail.Subject)
Catch ex As GraphException
    Console.WriteLine("An error occurred: {0}.", ex.Message)
Catch ex As Exception
    Console.WriteLine("An error occurred: {0}", ex.ToString())
End Try

IAsyncResult pattern (Begin/End methods) 

The Asynchronous Programming Model (APM) pattern, also known as IAsyncResult (or Begin/End) pattern, was introduced in .NET 1.0. When you reference Rebex assemblies for .NET 2.0 in your project, this is the pattern you can use. 

// start async operation, specify callback
IAsyncResult ar = pop3.BeginGetMessageList(Pop3ListFields.FullHeaders, GetMessageListFinished, null);

' start async operation, specify callback
Dim ar = pop3.BeginGetMessageList(Pop3ListFields.FullHeaders, AddressOf GetMessageListFinished, Nothing)

Sample asynchronous callback method:

// this method is called when the Begin method is completed
private void GetMessageListFinished(IAsyncResult ar)
{
    try
    {
        // get operation result
        Pop3MessageCollection list = pop3.EndGetMessageList(ar);

        // show result
        Console.WriteLine("Listed {0} item(s).", list.Count);
    }
    catch (Pop3Exception ex)
    {
        if (ex.Status == Pop3ExceptionStatus.OperationAborted)
            Console.WriteLine("Operation was canceled.");
        else
            Console.WriteLine("An error occurred: {0}.", ex.Message);
    }
    catch (Exception ex)
    {
        Console.WriteLine("An error occurred: {0}", ex.ToString());
    }
}

' this method is called when the Begin method is completed
Sub GetMessageListFinished(ByVal ar As IAsyncResult)
    Try
        ' get operation result
        Dim list As Pop3MessageCollection = pop3.EndGetMessageList(ar)

        ' show result
        Console.WriteLine("Listed {0} item(s).", list.Count)
    Catch ex As Pop3Exception
        If ex.Status = Pop3ExceptionStatus.OperationAborted Then
            Console.WriteLine("Operation was canceled.")
        Else
            Console.WriteLine("An error occurred: {0}.", ex.Message)
        End If
    Catch ex As Exception
        Console.WriteLine("An error occurred: {0}", ex.ToString())
    End Try
End Sub

Using IAsyncResult in .NET 4.0 or later 

If you reference Rebex assemblies for .NET 4.0 or later from your project, but still wish to use the old-style IAsyncResult asynchronous pattern, include the Rebex.Legacy namespace.

By default, .NET 4.0 assemblies only present a Task-based pattern (TAP) asynchronous API. Rebex.Legacy namespace defines all the Begin/End methods as extension methods, making it possible to use to easily port old code to .NET 4.0 or higher. 

using Rebex.Legacy;

Imports Rebex.Legacy

SynchronizationContext support for events 

When an asynchronous method on the GraphClient object raises an event, it's dispatched using the synchronization context captured when the operation was started.

This greatly simplifies writing GUI applications (Windows Forms and WPF) because all the events are raised on the applications GUI thread, eliminating the need to explicitly marshal the calls using the Invoke method.

If you need to disable this functionality, set GraphClient.Settings.RaiseEventsFromCurrentThread to true. This will cause all the events to be raised on the background operation's thread.

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