プログラムが少し作業を行う間、ユーザーを少しの間待たせる前に、StatusBar に TextBlock の Text を設定したいと考えています。
どうやら、このような素敵な小さな機能を実行する代わりに (これは機能しません):
Function Load(ByVal Id As Guid) As Thing
Cursor = Cursors.Wait
TextBlockStatus.Text = "Loading..."
TextBlockStatus.UpdateLayout()
Dim Found = From t In db.Thing _
Where t.Id = Id _
Select t
TextBlockStatus.Text = String.Empty
Cursor = Cursors.Arrow
Return Found
End Function
代わりに、この怪物を使用する必要があります。
Private WithEvents LoadWorker As BackgroundWorker
Private Sub Window1_Loaded(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs) Handles MyBase.Loaded
InitializeLoadWorker()
End Sub
Private Sub InitializeLoadWorker()
LoadWorker = New BackgroundWorker
LoadWorker.WorkerSupportsCancellation = False
LoadWorker.WorkerReportsProgress = False
AddHandler LoadWorker.DoWork, AddressOf LoadBackgroundWorker_DoWork
AddHandler LoadWorker.RunWorkerCompleted, AddressOf LoadBackgroundWorker_RunWorkerCompleted
End Sub
Sub Load(ByVal Id As Guid)
Cursor = Cursors.Wait
LoadWorker.RunWorkerAsync(Argument)
End Sub
Private Sub LoadBackgroundWorker_DoWork(ByVal sender As Object, ByVal e As DoWorkEventArgs)
Dim Worker As BackgroundWorker = DirectCast(sender, BackgroundWorker)
Dim Id As Guid = DirectCast(e.Argument, Guid)
e.Result = From t In db.Thing _
Where t.Id = Id _
Select t
End Sub
Private Sub LoadBackgroundWorker_RunWorkerCompleted(ByVal sender As Object, ByVal e As RunWorkerCompletedEventArgs)
TextBlockStatus.Text = String.Empty
Cursor = Cursors.Arrow
Dim Found As Thing = DirectCast(e.Result, Thing)
'now do something with the found thing here instead of where Load() is called.'
End Sub
そして、Load() 関数は Sub になりました!!
このような単純な状況を処理するためのより良い方法があるはずです。これは非同期である必要はありません。