"The calling thread cannot access this object because a different thread owns it"

Question

I have a WPF application that uses multi-threading to perform notifications. But I've faced the problem with "The calling thread cannot access this object because a different thread owns it." exception.

When my main window is loaded I create a new thread for notification window

private void RibbonWindow_Loaded(object sender, RoutedEventArgs rae)
{
    Thread newWindowThread = new Thread(new ThreadStart(() =>
    {
        var reminders = new List<Reminder>();

        // Go to the database to get active reminders...

        var notificationsViewModel = new NotificationsViewModel(reminders);
        var notificationsView = new NotificationsView();
        notificationsView.DataContext = notificationsViewModel;
        var checkAccess = notificationsView.Dispatcher.CheckAccess();

        if (checkAccess)
        {
            notificationsView.Show();
        }

        System.Windows.Threading.Dispatcher.Run();
    }));

    newWindowThread.IsBackground = true;
    newWindowThread.SetApartmentState(ApartmentState.STA);
    newWindowThread.Start();
}

Constructor for view is default:

public partial class NotificationsView : Window
{
    public NotificationsView()
    {
        InitializeComponent();
    }
}

Constructor for view model and model to bind

public NotificationsViewModel(List<ReminderCommon> reminders)
{
    this.Reminders = reminders;

    this.ReminderModel = reminders.First();
}

public ReminderCommon ReminderModel
{
    get
    {
        return this.m_ReminderModel;
    }
    set
    {
        this.m_ReminderModel = value;

        base.OnPropertyChanged("ReminderModel");
    }
}

Finally, my view

<Border BorderThickness="1" Background="Beige" BorderBrush="DarkKhaki" CornerRadius="5">
    <StackPanel Margin="5">
        <TextBlock Text="{Binding ReminderModel.Message}" TextWrapping="NoWrap" Margin="5" FontWeight="Bold"></TextBlock>
        <TextBlock Text="{Binding ReminderModel.DateFormatted}" TextWrapping="NoWrap" Margin="5"></TextBlock>
        <TextBlock Text="{Binding ReminderModel.Patient}" TextWrapping="NoWrap" Margin="5"></TextBlock>
        <TextBlock Text="{Binding ReminderModel.PatientPhoneNumbers}" TextWrapping="Wrap" Margin="5"></TextBlock>
        <TextBlock Text="{Binding ReminderModel.Doctor}" TextWrapping="NoWrap" Margin="5"></TextBlock>
        <CheckBox IsChecked="{Binding ReminderModel.IsCompleted}" Margin="5" />
    </StackPanel>
</Border>
</Border>

I receive exception on

notificationsView.Show();

Exception details

at System.Windows.Threading.Dispatcher.VerifyAccess()
at System.Windows.DependencyObject.GetValue(DependencyProperty dp)
at System.Windows.Media.SolidColorBrush.get_Color()
at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Controls.Primitives.BulletDecorator.ArrangeOverride(Size arrangeSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Controls.Control.ArrangeOverride(Size arrangeBounds)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Controls.StackPanel.ArrangeOverride(Size arrangeSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Controls.Grid.ArrangeOverride(Size arrangeSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at MS.Internal.Helper.ArrangeElementWithSingleChild(UIElement element, Size arrangeSize)
at System.Windows.Controls.ContentPresenter.ArrangeOverride(Size arrangeSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Documents.AdornerDecorator.ArrangeOverride(Size finalSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Controls.Border.ArrangeOverride(Size finalSize)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Window.ArrangeOverride(Size arrangeBounds)
at System.Windows.FrameworkElement.ArrangeCore(Rect finalRect)
at System.Windows.UIElement.Arrange(Rect finalRect)
at System.Windows.Interop.HwndSource.SetLayoutSize()
at System.Windows.Interop.HwndSource.set_RootVisualInternal(Visual value)
at System.Windows.Interop.HwndSource.set_RootVisual(Visual value)
at System.Windows.Window.SetRootVisual()
at System.Windows.Window.SetRootVisualAndUpdateSTC()
at System.Windows.Window.SetupInitialState(Double requestedTop, Double requestedLeft, Double requestedWidth, Double requestedHeight)
at System.Windows.Window.CreateSourceWindow(Boolean duringShow)
at System.Windows.Window.CreateSourceWindowDuringShow()
at System.Windows.Window.SafeCreateWindowDuringShow()
at System.Windows.Window.ShowHelper(Object booleanBox)
at System.Windows.Window.Show()
at Dentist.MainWindow.<RibbonWindow_Loaded>b__0() in D:\development\Dental Soft\Lotus\AMS\Dentist\MainWindow.xaml.cs:line 210
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state)
at System.Threading.ThreadHelper.ThreadStart()

TargetSite: {Void VerifyAccess()}

Also I mentioned two strange things: this code perfectly works in Windows 8, but doesn't work in Windows 7 and Windows XP and when I delete <CheckBox IsChecked="{Binding ReminderModel.IsCompleted}" Margin="5" /> from view code works. The same exceptions occurs if I use <Button /> (just control, without any bindings!)

Answer 1

You do not need another thread just to have another window running in parallel. Only do data-related actions on a background thread, do not create GUI elements there.