WPF .Net update Progress Bar while loading Classes

Question

I am creating a WPF MVVM Application where I have a Main Window and different Pages displayed in a Frame. I want to add a Loading Screen with a Progress Bar which updates while the Instances for the Pages get created:

Dim customer_page as new Pg_Custommer

Because there are Databases in some Pages, which get read while creating a new Instance, this takes some Time. I have tried to solve this with a Background Worker, but this did not work because the Thread has no Access to GUI (no STA-Thread). I need a Way to update the Progress Bar after each Class gets loaded.

Maybe someone could tell me how to solve this with a Dispatcher(No idea how these work) or similar.

Thanks in advance and Greetings from Switzerland

Answer 1

The SplashScreen ist a WPF Form with just Code behind, no VMMW, for testing. So i can adress the Progress Bar Value directly.

This is my Example Code:

Public Class SplashScreen

    Public Sub New()
        InitializeComponent()
    End Sub

    Private Async Function LoadClassesTask() As Task

        Dim progress = New Progress(Of Integer)(Sub(percent)
                                                    ProgressBar.Value = percent
                                                End Sub)

        Await Task.Factory.StartNew(FDoWork(progress), CancellationToken.None, TaskCreationOptions.None, TaskScheduler.FromCurrentSynchronizationContext())

    End Function

    Public Shared Function FDoWork(progress As IProgress(Of Integer)) As Action

        Dim i As Integer = 0


        'Create New Instances of Page-Classes

        customerpage = New Pg_Customer
        i += intLoadingProgress ' -> Global Integer = 9
        If progress IsNot Nothing Then progress.Report(i)

        pdfpage = New Pg_PDF_View
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        editorpage = New Pg_Editor
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        accpage = New Pg_Accounting
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        accselectpage = New Pg_AccountingSelect
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        tyreprotokollpage = New Pg_Tyreprotokoll
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        dbselectpage = New Pg_DatabaseSelect
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        dbRG = New Pg_Database_RG
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        dbAP = New Pg_Database_AP
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        dbMP = New Pg_Database_MP
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        dbSP = New Pg_Database_SP
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        pganalyzer = New Pg_DocAnalyzer
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        dashboardpage = New Pg_Dashboard
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        delivernotespage = New Pg_DeliveryNotes
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        dbCar = New Pg_Database_Car
        i += intLoadingProgress
        If progress IsNot Nothing Then progress.Report(i)

        Return Nothing
    End Function

    Private Sub Btn_Start_Click(sender As Object, e As RoutedEventArgs) Handles Btn_Start.Click

        LoadClassesTask()

    End Sub

End Class

It Runs now like this, but still the Page freezes and Progress Bar gets updated after all Classes are instantiated.

I guess im making a very stupid mistake somewhere but i just cant find it.