"The calling thread must be STA, because many UI components require this" error when creating a WPF pop-up Window in thread

For the thread that you're trying to start the GUI element in, you need to set the apartment state of the thread to STA BEFORE you start it.

Example:

myThread.SetApartmentState(ApartmentState.STA);
myThread.Start();

Absolutely Dispatcher is only way to do something (in specific Thread) when we work with multi-threading in WPF!

But for work with Dispatcher we must know 2 things:

1. Too many way to use Dispatcher like Dispatcher_Operation , [window.dispatcher] or etc.
2. We must call dispatcher in the main thread of app (that thread is must be STA thread)

So for example: if we want show other window[wpf] in another thread, we can use this code:

Frmexample frmexample = new Frmexample();
            frmexample .Dispatcher.BeginInvoke //Updated the variable name
                (System.Windows.Threading.DispatcherPriority.Normal,
                (Action)(() =>
                {
                    frmexample.Show();
                    //---or do any thing you want with that form
                }
                ));

Tip: Remember - we can't access any fields or properties from out dispatcher, so use that wisely