How to write an Async Sub in VB.NET? - vb.net

Question

Public Class LoginManager
Implements ILoginManager
Private ReadOnly _iLoginRepository As ILoginRepository
Public Sub New()
_iLoginRepository = New LoginRepository()
End Sub
Public Async Sub InsertFailedLoginAttempt(failedLoginAttempt As FailedLogin) Implements ILoginManager.InsertFailedLoginAttempt
'Example of the S in Solid (Single Repsonsibilty)
'Need to call these method async. But await errors
_iLoginRepository.InsertFailedLoginAttemptAsync(failedLoginAttempt)
_iLoginRepository.InsertFailedLoginAttemptIntoLoginMasterAsync(failedLoginAttempt)
End Sub
End Class
Repsoitory Interface:
Public Interface ILoginRepository
Function IsUserAuthenticatedAsync(ByVal cID As String, ByVal password As String, ByVal IsExternalUser As Boolean) As Task(Of Boolean)
Sub InsertFailedLoginAttemptAsync(ByVal failedLoginAttempt As FailedLogin)
Sub InsertFailedLoginAttemptIntoLoginMasterAsync(ByVal failedLoginAttempt As FailedLogin)
End Interface
Repository Implementation:
Public Class LoginRepository
Implements ILoginRepository
Public ReadOnly _applicationDBContext As New ApplicationDBContext()
Public Async Sub InsertFailedLoginAttemptAsync(failedLoginAttempt As FailedLogin) Implements ILoginRepository.InsertFailedLoginAttemptAsync
Using _applicationDBContext
_applicationDBContext.RepFailedLogins.Add(failedLoginAttempt)
Await _applicationDBContext.SaveChangesAsync()
End Using
End Sub
Public Async Sub InsertFailedLoginAttemptIntoLoginMasterAsync(failedLoginAttempt As FailedLogin) Implements ILoginRepository.InsertFailedLoginAttemptIntoLoginMasterAsync
Using _applicationDBContext
_applicationDBContext.RepFailedLoginMasters.Add(failedLoginAttempt)
Await _applicationDBContext.SaveChangesAsync()
End Using
End Sub
''' <summary>
''' Determine whether a user is authenticated, be it an internal or external user
''' I have condensed two methods into one
''' </summary>
''' <param name="cID"></param>
''' <param name="password"></param>
''' <param name="IsExternalUser"></param>
''' <returns></returns>
Public Async Function IsUserAuthenticatedAsync(cID As String, password As String, IsExternalUser As Boolean) As Task(Of Boolean) Implements ILoginRepository.IsUserAuthenticatedAsync
If (IsExternalUser And String.IsNullOrEmpty(password)) Then
Throw New ArgumentNullException("External user requires password")
End If
Dim user As Chaser
Dim toRet As Boolean
Using _applicationDBContext
'Two ways to use LINQ
'First is LINQ Lambda sybntax(little harder to read)
user = Await _applicationDBContext.Chasers.Where(Function(x) x.CID = cID).FirstOrDefaultAsync()
'Second is LINQ Query syntax(looks more like SQL just more verbose
'user = From x In _applicationDBContext.Chasers
' Where x.CID = cID
' Select x
End Using
If IsNothing(user) Then
toRet = False
ElseIf Not IsExternalUser And Not IsNothing(user) Then
toRet = True
ElseIf IsExternalUser And user.Hash_Password = password Then
toRet = True
End If
Return toRet
End Function
End Class
I'm trying to call the InsertFailedLoginAttemptAsync repository method in my manager. It is an async method but I am unable to await the method. How can I make this method awaitable?
I believe it has something to do with the interface and not making it an async method like in C# but I'm unable to do this.

Answer 1

Subs should not be async. Event handlers are the only exception to that rule. You await Task which can only be returned from a Function. If the intention is to make that interface async then all the members need to be functions that return a Task or its derivative.
Async is something that bubbles all the way through when used. That said the ILoginManager along with the ILoginRepository should be refactored (if possible) to follow the proper syntax.
Reference: Async/Await - Best Practices in Asynchronous Programming

Answer 2

Fixed via Nkosi's reply:
Interface:
Public Interface ILoginRepository
Function IsUserAuthenticatedAsync(ByVal cID As String, ByVal password As String, ByVal IsExternalUser As Boolean) As Task(Of Boolean)
Function InsertFailedLoginAttemptAsync(ByVal failedLoginAttempt As FailedLogin) As Task
Function InsertFailedLoginAttemptIntoLoginMasterAsync(ByVal failedLoginAttempt As FailedLogin) As Task
End Interface
Manager method:
Public Async Function InsertFailedLoginAttempt(failedLoginAttempt As FailedLogin) As Task Implements ILoginManager.InsertFailedLoginAttempt
'Example of the S in Solid (Single Repsonsibilty)
Await _iLoginRepository.InsertFailedLoginAttemptAsync(failedLoginAttempt)
Await _iLoginRepository.InsertFailedLoginAttemptIntoLoginMasterAsync(failedLoginAttempt)
End Function