How do I cede focus to the previous application in Cocoa?

Let's saying the user is currently on Chrome. So I have a HUD that is invoked by开发者_运维知识库 a global hotkey, the user then types something into it and on clicking Close or OK, the HUD goes away (just using [NSPanel orderOut:]) but my application is still focused (i.e. the Menu bar of my application is still visible). But I want the focus to go back to original application, Chrome. How do I achieve something like this? Ideally, I'd also be able to never "get" focus to my application and hence, the HUD input would all happen while Chrome was still the focused application. Things.app manages to achieve something like this. Quicksilver does this too.

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Call [NSApp hide:]

That will hide your application and activate the previously-active application.

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In order to never get the focus on your application call [panel setStyleMask:[panel styleMask] | NSNonactivatingPanelMask]; on your NSPanel or check the Non Activating checkbox on your NSPanel in Interface Builder.

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You can either have a faceless helper app that does this for you or get the PSN of the frontmost process before you're brought forward and switch back to it when you want to go away.

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If this is the only UI that your application has to offer, you can give it an LSUIElement Info.plist key, which prevents it from being in the Dock or being the active application.