When the Window class is instantiated, it is not visible by default. Show shows a window and returns immediately, without waiting for the window to be closed. Consequently, the opened window does not prevent users from interacting with other windows in the application. This type of window is called a modeless window. Common examples of modeless windows are properties windows, toolboxes, and palettes. To restrict a user to interacting with a specific window, the window must be opened by calling ShowDialog.
A window that is opened by calling Show does not automatically have a relationship with the window that opened it; specifically, the opened window does not know which window opened it. This relationship can be established using the Owner property and managed using the OwnedWindows property.
Calling Show achieves the same end result as setting Visibility property of the Window object to Visible. However, there is a difference between the two from a timing perspective.
Calling Show is a synchronous operation that returns only after the Loaded event on the child window has been raised:
Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)