Start a GUI process in Mac OS X without dock icon

I have an application that normally runs with a standard graphical interface. However, for certain long-running tasks, it spawns additional processes of the same application that run in a "script mode," where I am controlling it from the parent process. Everyth开发者_JS百科ing works great, except that for each child process I get another dock icon that pops in for a second or two and then disappears.

Is there a way to run an application sometimes without the application icon showing up on the dock? I can't edit the info.plist or anything because normally I want the dock icon. The option must be able to be set by changing a property on the process or via a command line parameter. I have full control over the source to the application. It is written in C++ (Qt), but solutions that target the native Cocoa library are fine.

If I put this code into a separate application it would cause major duplication, so I'd rather keep it the way it is. I cannot run the long-running tasks in background threads because they are doing things that must be done in a GUI thread. (In Qt, you cannot reliably use fonts, pixmaps, or render SVG content onto a QGraphicsScene on background threads.)

Any solutions?

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Motivated from here, you can do:

[NSApp setActivationPolicy: NSApplicationActivationPolicyAccessory];

or

[NSApp setActivationPolicy: NSApplicationActivationPolicyProhibited];

This should hide the dock icon. See here for some documentation about NSApplicationActivationPolicy.

In Python, the code to hide the dock icon is:

# https://stackoverflow.com/a/9220857/133374
import AppKit
# https://developer.apple.com/library/mac/#documentation/AppKit/Reference/NSRunningApplication_Class/Reference/Reference.html
NSApplicationActivationPolicyRegular = 0
NSApplicationActivationPolicyAccessory = 1
NSApplicationActivationPolicyProhibited = 2
AppKit.NSApp.setActivationPolicy_(NSApplicationActivationPolicyProhibited)

See also the related question "How to hide the Dock icon".

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If you want to avoid that the dock icon pops up at all right at the beginning, you can do that:

import AppKit
info = AppKit.NSBundle.mainBundle().infoDictionary()
info["LSBackgroundOnly"] = "1"

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import AppKit
info = AppKit.NSBundle.mainBundle().infoDictionary()
info["LSBackgroundOnly"] = "1"

This code works for my Non-GUI background python script.