Talking back to the interface using Delegates and Events in VB.NET

I love using Async and Await. It makes asynchronous programming so much easier. One area I have never really liked though is the functionality for talking back to the main thread (like the UI thread) when you are doing asynchronous things though. Something I have started doing recently (and for some reason had lost from my toolbox of techniques) is the use of Delegates and Events. In the class that has a method that runs asynchronously, I delcare some public events. These events can then be tied up on the UI thread. Then when the event is raised in the asynchronous method, the call is made back to the UI thread and it has the correct context. I haven't looked in depth into how this achieved but it works very well and gives the class with the async method on it a lot of flexbility as it's not tied to the calling class in anyway.

	Imports System.Data.SqlClient

	Module Updater

	Sub Main()
	Console.WriteLine("Welcome to the cool async updater")

	dim updater = New DatabaseUpdater(new UpdateScanner())
	addHandler updater.ErrorRaised, AddressOf InformUserOfError
	AddHandler Updater.Success, AddressOf InformUserOfSuccess

	dim updaterRun = Task.Factory.StartNew(Async Sub() Await updater.Run())
	updaterRun.Wait()

	Console.ReadKey()
	End Sub

	Private Sub InformUserOfSuccess(eventdetails As ExecutionResult)
	Dim color = console.BackgroundColor

	If eventdetails.Success then
	Console.ForegroundColor = ConsoleColor.Green

	Console.WriteLine("You did it! Teh Updates ran")
	Console.WriteLine(eventdetails.Message)
	Else
	Console.ForegroundColor = ConsoleColor.Yellow

	Console.WriteLine("Oh man there were problems")
	Console.WriteLine(eventdetails.Message)
	End If

	Console.ForegroundColor = color
	End Sub

	Private Sub InformUserOfError(eventdetails As ExecutionResult)
	dim color = console.ForegroundColor
	Console.ForegroundColor = ConsoleColor.Red

	Console.WriteLine("{0}, {1}", eventdetails.Message, eventdetails.Exception.Message)

	Console.ForegroundColor = color
	End Sub
	End Module

	public delegate sub SuccessEvent(eventDetails As ExecutionResult)
	Public Delegate Sub ErrorEvent(eventDetails as ExecutionREsult)

	Public Class DatabaseUpdater
	public Event Success as SuccessEvent
	public Event ErrorRaised as ErrorEvent

	Private ReadOnly _updateScanner As IUpdateScanner

	public Sub New (updateScanner As IUpdateScanner)
	Me._updateScanner = updateScanner
	end Sub

	public Async function Run() As Task
	Dim updates = Me._updateScanner.Updates().ToArray()
	dim failed as Integer

	If updates.Any() then
	try
	Using conn as New SqlConnection("")
	await conn.OpenAsync()

	for each u in updates
	dim result = Await Update(u, conn)

	If result = false
	failed = failed + 1
	End If
	Next

	conn.Close()
	End Using
	Catch ex As Exception
	RaiseEvent ErrorRaised(New ExecutionResult(false, "Unable to create the connection", ex))

	return
	End Try

	End If

	RaiseEvent Success(new ExecutionResult(failed = 0, $"{updates.Count() - failed} of {updates.Count()} Updates completed successfully", nothing))
	End function

	Async Function Update(updateCommand As string, conn As SqlConnection) as Task(Of boolean)
	Try
	Using command As New SqlCommand(updateCommand, conn)
	command.CommandType = CommandType.Text

	Await command.ExecuteNonQueryAsync()
	End Using
	Catch ex As Exception
	RaiseEvent ErrorRaised(new ExecutionResult(False, $"There was an error running the update `{updateCommand}`", ex))

	return false
	End Try

	return true
	End Function
	End Class

	Public Class ExecutionResult
	Property Success() As boolean
	Property Message() As string
	Property Exception() As Exception

	Public sub New(success As Boolean, message As String, exception As Exception)
	me.Success = success
	me.Message = message
	me.Exception = exception
	End sub
	End Class

	public Interface IUpdateScanner
	function Updates() As IEnumerable(of string)
	End Interface

	Public Class UpdateScanner
	Implements IUpdateScanner

	Public Function Updates() As IEnumerable(Of String) Implements IUpdateScanner.Updates
	Dim list = New List(Of String)()
	list.Add("CREATE TABLE [dbo].[Pet](
	[Type] [int] NULL
	) ON [PRIMARY]")
	list.Add("CREATE TABLE [dbo].[Pie](
	[Type] [int] NULL
	) ON [PRIMARY]")
	Return list
	End Function
	End Class