C# Hiding an application from the taskbar

Question

I have been struggling to hide another application from the taskbar from my application.
I have been using the SetWindowLong function in order to set/remove WS_EX_APPWIN

Answer 1

The rules for determining which windows have buttons on the taskbar are documented on MSDN. Raymond Chen gives the following summary of these rules:

There are some basic rules on which windows go into the taskbar. In short:

• If the WS_EX_APPWINDOW extended style is set, then it will show (when visible).
• If the window is a top-level unowned window, then it will show (when visible).
• Otherwise it doesn't show.

The fact that you are trying to modify a window in another app severely hampers you. You are removing the WS_EX_APPWINDOW extended style. This is not enough because the window in question will be a top-level unowned window (see bullet point 2). You cannot change the owner of a window once it has been created and since the window is controlled by another process you are pretty much stuck.

The only option remaining is to remove the WS_EX_APPWINDOW extended style and replace it with WS_EX_TOOLWINDOW. This will indeed get the window off the taskbar but it will change the appearance of the window:

The window is intended to be used as a floating toolbar. A tool window has a title bar that is shorter than a normal title bar, and the window title is drawn using a smaller font. A tool window does not appear in the taskbar or in the dialog that appears when the user presses ALT+TAB. If a tool window has a system menu, its icon is not displayed on the title bar. However, you can display the system menu by right-clicking or by typing ALT+SPACE.