WPF MVVM background printing databinding problem

I am developing a point-of-sale application using wpf / mvvm. For many periods of the transaction life cycle, receipts will be printed in the background. I used other examples to generate and print receipts in the background. I am printing UserControl in the background and everything looks great.

Then I created a ViewModel for the control so that it can load the transaction for printing. I started with two main text fields: the text heading “Client receipt” and the top heading “Printed in: MM / dd / yy hh: mm tt”.

This is how the debugger shows the life cycle when I press the print button:

• Creates a new instance of the control.
• Creates a new instance of ViewModel
• Sets text for INPC properties
• Performs a measure on the control to get the desired size before printing
• Loads a print dialog and returns a print queue for names
• Scales the size of the control to match the receipt (no need to scale for my current selected printer, as the ImageArea width is set the same as my UC)
• Modifies and arranges the grid based on the "new" size of the scalable image.
• calls PrintDialog.PrintVisual - sending UserControl
• The printer prints a receipt - without a text file
• Then my debugger goes into get {return _HeaderText; } part of the code - after the control has already been printed.

, ? , , ​​ , , CC ( ).

?

PrintReceipt:

ClientReceiptView control = new ClientReceiptView(Message);       
System.Windows.Controls.PrintDialog printDlg = new System.Windows.Controls.PrintDialog();
PrintQueue ReceiptPrinter = new LocalPrintServer().GetPrintQueue("CITIZEN CT-S310");
PrintCapabilities PC = ReceiptPrinter.GetPrintCapabilities();
printDlg.PrintQueue = ReceiptPrinter;
control.Measure(new Size(Double.PositiveInfinity, Double.PositiveInfinity));
Size PreGridSize = control.DesiredSize;
double Scale = Math.Min(PC.PageImageableArea.ExtentWidth / PreGridSize.Width, PC.PageImageableArea.ExtentHeight / PreGridSize.Height);
control.LayoutTransform = new System.Windows.Media.ScaleTransform(Scale, Scale);
Size PaperSize = new Size(PC.PageImageableArea.ExtentWidth, Math.Min(PC.PageImageableArea.ExtentHeight, PreGridSize.Height));
control.Measure(PaperSize);
Point ptGrid = new Point(PC.PageImageableArea.OriginWidth, PC.PageImageableArea.OriginHeight);
control.Arrange(new Rect(ptGrid, PaperSize));
printDlg.PrintVisual(control, "My App");

( )

public ClientReceiptView(string Header)
{
    InitializeComponent();
    vm = new ClientReceiptViewModel(Header);
    this.DataContext = vm;
}

ViewModel:

public class ClientReceiptViewModel : ViewModelBase
{
    #region Properties

    private string _HeaderText;

    public string HeaderText
    {
        get { return _HeaderText; }
        set { _HeaderText = value; OnPropertyChanged("HeaderText"); }
    }

    private int _TripID;

    public int TripID
    {
        get { return _TripID; }
        set { _TripID = value; OnPropertyChanged("TripID"); }
    }

    private string _PrintedOn;

    public string PrintedOn
    {
        get { return _PrintedOn; }
        set { _PrintedOn = value; OnPropertyChanged("PrintedOn"); }
    }

    #endregion

    public ClientReceiptViewModel(string Header)
    {
        HeaderText = Header;
        TripID = 2220013;
        PrintedOn = "Printed: " + DateTime.Now.ToString("MM/dd/yy hh:mm tt");
    }
}

: / OnPropertyChanged ( "HeaderText" ):

Namespace.Main.POS.Receipts.ClientReceiptViewModel.PrintedOn.set(string value) Line 38  C#
Namespace.Main.POS.Receipts.ClientReceiptViewModel.SetData(string Header) Line 79 + 0x4f bytes  C#
Namespace.Main.POS.Receipts.ClientReceiptView.ClientReceiptView(string Header) Line 28 + 0x13 bytes C#
Namespace.Main.POS.Receipts.PrintReceipt.PrintClientReceipt(string Message) Line 12 + 0x1e bytes    C#
Namespace.Main.MainWindowView.button1_Click(object sender, System.Windows.RoutedEventArgs e) Line 23 + 0xb bytes    C#
PresentationCore.dll!System.Windows.RoutedEventHandlerInfo.InvokeHandler(object target, System.Windows.RoutedEventArgs routedEventArgs) + 0x78 bytes    
PresentationCore.dll!System.Windows.EventRoute.InvokeHandlersImpl(object source, System.Windows.RoutedEventArgs args, bool reRaised) + 0xbe bytes   
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PresentationCore.dll!System.Windows.Interop.HwndMouseInputProvider.FilterMessage(System.IntPtr hwnd, MS.Internal.Interop.WindowMessage msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x67d bytes 
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printDlg.PrintVisual(, " " ); , , get {return _PrintedOn; }

Namespace.Main.POS.Receipts.ClientReceiptViewModel.PrintedOn.get() Line 37  C#
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WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs) + 0x53 bytes 
WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source, System.Delegate method, object args, int numArgs, System.Delegate catchHandler) + 0x42 bytes    
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WindowsBase.dll!System.Windows.Threading.Dispatcher.WndProcHook(System.IntPtr hwnd, int msg, System.IntPtr wParam, System.IntPtr lParam, ref bool handled) + 0x63 bytes 
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WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o) + 0x7d bytes    
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs) + 0x53 bytes 
WindowsBase.dll!MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(object source, System.Delegate method, object args, int numArgs, System.Delegate catchHandler) + 0x42 bytes    
WindowsBase.dll!System.Windows.Threading.Dispatcher.InvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs) + 0xb4 bytes    
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Microsoft.VisualStudio.HostingProcess.Utilities.dll!Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssemblyDebugInZone() + 0x23 bytes   
mscorlib.dll!System.Threading.ThreadHelper.ThreadStart_Context(object state) + 0x63 bytes   
mscorlib.dll!System.Threading.ExecutionContext.Run(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state, bool ignoreSyncCtx) + 0xb0 bytes    
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