ansaurus

Question

Qt use-case for same signal to 2 slots on same object?

Answer 1

+2 A:

This is for cases when you have something like one button that changes two parts of another. It may sound silly, but it would be equivalent to calling the second slot function from the first slot.

Say, clicking the play/pause button makes the stop button active or in active and also changes the tool tip. This could easily be done with one slot, but you may want the option to do them independently other times. To promote reuse, you use the above method of connecting one signal to 2 slots.

Adam W 2010-01-08 15:03:39

Thanks Adam. Looks silly to me though: I would promote an abstraction where the emitter of the signal doesn't need to care what needs to happen on the sink side.

jldupont 2010-01-08 15:07:34

@jldupont : The emitter of the signal doesn't have to care about what needs to happen on the sink side. It just emits the signal and goes on with its task. The one making the connection doen't have to be the emitter, a connection can very well be made by the sink, or even by a third party (if the signal and the slots are public).

Fred 2010-01-08 15:39:59

To continue with what Fred said, I almost always find it the case that the sink makes the connection (directly or through a proxy). Having a source that knows all the sinks directly somewhat defeats the purpose. And as Fred said, remember that whatever emits the signal doesn't care who receives it. However it may run the slot code before it continues depending on the connection type and threading.

Adam W 2010-01-08 16:25:56

Continuing on Fred and Adam, my experience is that the connections almost always are made by a third party, i.e. the parent of both. Either, in a visual case, the c'tor of the outer window, or, when it comes to singletons and other classes managing application states, the main function.

e8johan 2010-01-08 21:52:45

Answer 2

+1 A:

It would allow other objects to trigger slot1 and slot2 separately.

connect( Object1, Signal1, Object2, slot1 );
connect( Object1, Signal1, Object2, slot2 );
connect( Object3, Signal1, Object2, slot1 );
connect( Object4, Signal1, Object2, slot2 );

William 2010-01-08 15:11:30

Answer 3

A:

Hey,

It's actually a really powerful way of doing MVC... Let's say you want to "connect" views to listen to an object than emit datas...

You can connect a PieChart view with :

connect( MySourceModel, SIGNAL(newDataAreThere()), PieChartView, SLOT(notifyNewDataReceived()));

Later in your application, another module is created and need as well to listen to data... No problem :

connect( MySourceModel, SIGNAL(newDataAreThere()), AnotherView, SLOT(notifyNewDataReceived()));

You can connect/disconnect your views, and the model doesn't even know who are listening to him... That's not his problem...

I hope my little example is understandable ;)

Andy M 2010-01-12 22:05:05

thanks for your contribution **but** this did carefully read the question?

jldupont 2010-01-13 12:57:39

Oups, yeah, I read a bit too quickly your question... Sorry !

Andy M 2010-01-13 19:02:53

ansaurus

tags:

views:

answers:

Qt use-case for same signal to 2 slots on same object?

related questions