Adding a wpf button created in background thread to Mainwindow - wpf

Question

Here's my scenario : I have a simple wpf window with a button. When the user clicks on the button, I want to create another window (let's call it child window) and then create a wpf button on a background thread, add it to the child window and show the child window. Here's the code for this:
Button backgroundButton = null;
var manualResetEvents = new ManualResetEvent[1];
var childWindow = new ChildWindow();
manualResetEvents[0] = new ManualResetEvent(false);
var t = new Thread(x =>
{
backgroundButton = new Button { Content = "Child Button" };
childWindow.Dispatcher.BeginInvoke(DispatcherPriority.Normal, (Action)(() => childWindow.MainPanel.Children.Add(backgroundButton)));
manualResetEvents[0].Set();
});
t.SetApartmentState(ApartmentState.STA);
t.Start();
WaitHandle.WaitAll(manualResetEvents);
childWindow.ShowDialog();
When I call the ShowDialog(), I get this error "The calling thread cannot access this object because a different thread owns it.". I know that this error is because the button added to the child window is created on a background thread and hence we get this error. Question is: How do I get past this error and still have my button to be created on the background thread

Answer 1

You must use Dispatcher every time, when you want to access Parent's window from another thread. I see in action of your thread , you use backgroundButton . Because of that, you must do whatever with your button inside Dispathcer.BeginIvoke statement
[EDIT]
Change Thread action to this
var t = new Thread(x =>
{
backgroundButton.Dispatcher.BeginInvoke(DispatcherPriority.Normal, (Action)(() => backgroundButton = new Button { Content = "Child Button" }));
childWindow.Dispatcher.BeginInvoke(DispatcherPriority.Normal, (Action)(() => childWindow.MainPanel.Children.Add(backgroundButton)));
manualResetEvents[0].Set();
});
I wrote this according to your code.I doesn't check you code, but hope its right.