CODEWITHSUNDEEP
pythonpygobjectgobject
Suhas
Suhas

Reputation: 131

How can I maintain, atleast, some order in which callbacks connect to a signal?

When I simply use 'connect', there is no way I can specify the order in the callbacks will be called. Having connect_before and connect_after to connect before/after the default doesn't serve my purpose. I want something like connect_first and connect_last or anything else that will help me specify the order in which callbacks connect to a signal.

Something like this?

    something.connect_first('my-signal', callback1)
    somethingelse.connect_last('my-signal', callback2)

Upvotes: 0

Views: 226

Answers (1)

ebassi
ebassi

Reputation: 8815

There is only one explicit ordering guarantee for GObject signals:

  • the class closure added when creating a new signal with G_SIGNAL_RUN_FIRST will be called before all callbacks added using g_signal_connect()
  • the class closure added when creating a new signal eith G_SIGNAL_RUN_LAST will be called after all callbacks added using g_signal_connect() and before all callbacks added using g_signal_connect_after()

This means that you can only control whether a callback is invoked before or after all other callbacks connected manually when you're creating a new signal - for obvious reasons, since you may want to provide an initial state at the start of an emission chain, or you want to ensure a stable state at the end of an emission chain.

As for the order of the callbacks added using g_signal_connect(), there is no explicit guarantee of any ordering. There's an implicit order, the order of connection, though, that won't likely ever be changed. Remember that signal handlers can install new handlers, or disconnect them, or block the signal emission, so relying on a specific order is usually an indication of a design problem in the code.

Upvotes: 2

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