Open New Windows from Background Thread on ViewModel - wpf

Question

So I have a WPF application (MVVM) with a Splash Screen. On the splash screen startup I have a background thread on the ViewModel that does some start up related activities. In certain instances I want to open a couple of additional windows (user input needed etc...). I was getting a number of issues/errors/exceptions while trying to do this (mostly around that new window - also MVVM - trying to populate its UI items, such as combo boxes). So I've pulled back the issue to a simpler form - the "tempWindow" doesn't have anything so it doesn't throw UI population errors, but basically it does just open them and once the background thread is done, closes them all. If someone could point me in the right direction on what I am doing incorrectly here it would be appreciated.
The constructor for the ViewModel kicks off a background thread
public SplashScreenViewModel()
{
this.LoadingStatusText = "Starting Startup Processing ... ";
this.VersionNumber = "version " + System.Reflection.Assembly.GetExecutingAssembly().GetName().Version.ToString();
var threadBackgroundStartUpProcesses = new Thread(new ThreadStart(this.BackgroundStartUpProcesses));
threadBackgroundStartUpProcesses.SetApartmentState(ApartmentState.STA);
threadBackgroundStartUpProcesses.IsBackground = true;
threadBackgroundStartUpProcesses.Start();
}
The background thread, should just open three windows (which it does) but those windows should stay open (they disappear once the thread completes).
private void BackgroundStartUpProcesses()
{
for (int i = 0; i < 3; i++)
{
var objTempWindow = new tempWindow();
objTempWindow.Show();
}
}
// EDIT: updated with responses, now get an error when the TempWindow has a comboBox that is being populated from the TempWindowViewModel.
private void BackgroundStartUpProcesses()
{
for (int i = 0; i < 3; i++)
{
var objTempWindow = new tempWindow();
objTempWindow.Show();
}
System.Windows.Threading.Dispatcher.Run();
}
When it goes to open the TempWindow the exception: "The calling thread cannot access this object because a different thread owns it." is thrown and appears to be when a ComboBox on that Window is trying to be populated.

Answer 1

I suspect that windows need an owner and when the owner dies, so does the window. Opening the windows on the main thread makes them stick around. Something like this...
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
var threadBackgroundStartUpProcesses = new Thread(new ParameterizedThreadStart(this.BackgroundStartUpProcesses));
threadBackgroundStartUpProcesses.SetApartmentState(ApartmentState.STA);
threadBackgroundStartUpProcesses.IsBackground = true;
threadBackgroundStartUpProcesses.Start(System.Windows.Threading.Dispatcher.CurrentDispatcher);
}
private void BackgroundStartUpProcesses(object d)
{
System.Windows.Threading.Dispatcher dispatcher = (System.Windows.Threading.Dispatcher) d;
for (int i = 0; i < 3; i++)
{
dispatcher.BeginInvoke((Action)(() =>
{
var objTempWindow = new tempWindow();
objTempWindow.Show();
}));
}
}
}
edit
I've just done some digging on WPF threading and it looks like you can open windows on multiple threads, but you need to start the new dispatcher. See near the end of this page:
http://msdn.microsoft.com/en-us/library/ms741870.aspx
In your BackgroundStartupProcesses, under objTempWindow.Show() add this line
System.Windows.Threading.Dispatcher.Run();

Answer 2

Are you setting your MainWindow before closing the splash screen? WPF sets the first opened window of an application as the MainWindow and unless you've changed the ShutdownMode of your App.xaml then once you close the splash screen the application shuts down.