How to force an NSWindow to be in front of every app? Even fullscreen apps

Question

I have an NSWindow that i would like to have it in front of everything (every app of the computer, fullscreen apps, etc..). Even if i click in a background app, the NSWindow cant go to background. And the NSWindow must follow the user screen if, for example, the user switches the desktop to desktop2, and so on... How can i do that?
Thanks!

Answer 1

If you don't need to be visible with other apps' full-screen windows, it's not too hard.

First, to stay in front of everything else, just setLevel: with NSFloatingWindowLevel or higher. Experiment with the different values to see which seems appropriate to your needs.

Next, to stay in front even when the user changes Spaces, possibly including Exposé/Mission Control, setCollectionBehavior: with the appropriate pair of flags, or use the corresponding Spaces and Exposé settings in the Attributes Inspector if you're creating the window in the nib. Either Can Join All Spaces or Move to Active Space will make sure you stay visible on every space, in slightly different ways. You'll probably want Exposé set to Stationary, or possibly Transient, too. Again, try both ways and see.

However, Lion will hide both all-spaces and move-to-active-space windows when the user switches to a full-screen space or to Dashboard or Launchpad. And if you watch, you'll see that it does this in different ways for each of the three cases. And that Snow Leopard does things a little differently, and so does Mountain Lion.

If you want to solve that last problem, you need a bit of hackery—and different forms of hackery for each case and for each OS version. The basic trick is to catch the hide-related notifications and unhide yourself at the appropriate time.

Answer 2

You should modify your info.plist and set the Application is Agent flag to YES. An agent's window can be displayed in front of fullscreen windows.