(MVC) MVC (2018 год)

BackgroundWorkerQueue.

When you have receive list of URL to downloads (in cycle or after parser/webscraper was finished), you have only one way to download this list without freezing GUI of desktop apps - to use class, similar to this.


   1:  Imports System.ComponentModel
   2:   
   3:  Public Class BackgroundWorkerQueue
   4:   
   5:      Public Property ContinueOnError As Boolean
   6:      Private Property Queue As Queue(Of QueuedWorker)
   7:      Private Property DoWorkEventHandler As DoWorkEventHandler
   8:      Public Event QueueFinished()
   9:   
  10:      Public Sub New()
  11:          Me.Queue = New Queue(Of QueuedWorker)()
  12:      End Sub
  13:   
  14:      Public Sub Add(ByVal Worker As BackgroundWorker, ByVal Argument As Object, DoWorkEventHandler1 As DoWorkEventHandler)
  15:          DoWorkEventHandler = DoWorkEventHandler1
  16:          Me.Queue.Enqueue(New QueuedWorker(Worker, Argument))
  17:      End Sub
  18:   
  19:      Public Sub RunWorkerAsync()
  20:          Debug.Print("BackgroundWorker.Run(), {0} items in queue.", Me.Queue.Count)
  21:          Dim Q As QueuedWorker = Me.Queue.Dequeue()
  22:          AddHandler Q.Worker.RunWorkerCompleted, New RunWorkerCompletedEventHandler(AddressOf Me.Completed)
  23:          AddHandler Q.Worker.DoWork, DoWorkEventHandler
  24:          Q.Worker.RunWorkerAsync(Q.Argument)
  25:      End Sub
  26:   
  27:      Private Sub Completed(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
  28:          Debug.Print("BackgroundWorker.Completed()")
  29:          Dim Worker As BackgroundWorker = TryCast(sender, BackgroundWorker)
  30:          If Worker IsNot Nothing Then
  31:              RemoveHandler Worker.RunWorkerCompleted, AddressOf Me.Completed
  32:              RemoveHandler Worker.DoWork, DoWorkEventHandler
  33:              If (Me.ContinueOnError OrElse e.[Error] Is Nothing) AndAlso Me.Queue.Count > 0 Then
  34:                  Me.RunWorkerAsync()
  35:              ElseIf Queue.Count = 0 Then
  36:                  RaiseEvent QueueFinished()
  37:              End If
  38:          End If
  39:      End Sub
  40:  End Class
  41:   
  42:  Public Class QueuedWorker
  43:      Public Property Argument As Object
  44:      Public Property Worker As BackgroundWorker
  45:   
  46:      Public Sub New()
  47:      End Sub
  48:   
  49:      Public Sub New(ByVal Worker1 As BackgroundWorker, ByVal Argument1 As Object)
  50:          Worker = Worker1
  51:          Argument = Argument1
  52:      End Sub
  53:  End Class


Use this class at this pattern:




 ...    
 306:                  Dim BGWorkerQueue As New BackgroundWorkerQueue
 307:                  AddHandler BGWorkerQueue.QueueFinished, AddressOf BGWorkerQueueFinished
 308:                  Dim BGW3 As New BackgroundWorker
 309:                  For Each Link In LinkCollections
 ...    
 311:                      BGWorkerQueue.Add(BGW3, URL, AddressOf BGW3_DoWork)
 312:                  Next
 313:                  BGWorkerQueue.RunWorkerAsync()
 314:              End If
 315:          End If
 316:      End Sub
 317:   
 319:      Private Sub BGW3_DoWork(sender As Object, e As DoWorkEventArgs)
 ...    
 327:              Download(e.Argument, ...)
 ...    
 330:      End Sub
 ...:   
 342:      Sub BGWorkerQueueFinished()
 ...    
 353:      End Sub
 354:   




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