Question

I have in my application the standard UI-Thread and additional a second UI-Thread. Now, I create and show a Window in the second UI-Thread. After this, I should create and show a Dialog in the standard UI-Thread but it should be modal to the window, which was created and shown in the second UI-Thread. The reason is, that I have to create this Dialog in the standard UI-Thread, that this Dialog uses a Control which is not ThreadSafe.

Answer 1

You should just be able to set Owner property of the window:

newWindow.Owner = parentWindowFromOtherThread;