It is possible to set one Icon so, that it would be used on every window in current app. So that i set it once (not on every window by hand)..?
A good reference on the subject is here MSDN. States that you have an Icon for the Application (Desktop Icon), and one for each Window.
A WPF window always displays an icon. When one is not provided by setting Icon, WPF chooses an icon to display based on the following rules:
Use the assembly icon, if specified.
If the assembly icon is not specified, use the default Microsoft Windows icon.
Community Content Reference:
"A liitle tip : if you set the application icon and expect to see it on the window - it wont show up if running in debug from VS. Running externally or without attaching (ctrl + f5) the icon displays as expected."